Chapter 8 – “Contact!”

Chapter 8


At 200 ft altitude, a clear view of both the Challenger shadow with landing struts deployed, and the range of my westward trek to set up the ALSEP is visible to the left of this frame from the 16 mm DAC. The large ~50 m diameter crater to the right of the Challenger shadow is Rudolph (see Figs. 8.42↓, 8.43↓ for identification of features in this view). (From the original DAC landing sequence prepared for this chapter by Ben Feist[2])

Day Six – Landing in the Valley of Taurus-Littrow[3]

“Good Morning, America, how are you?” Joe Allen asked following LM TELEMU’s (Telemetry) transmission of John Denver’s version[4] of the “City of New Orleans”.

“This is America,” Evans replied as the only one of us with a Snoopy Cap on his head. “That’s a good way to wake up.”

“Good Morning, America, how are you? You’ll be gone a million miles before the mission is done,” Allen paraphrased the great song written by Steve Goodman and made famous by Arlo Guthrie and again later by Willie Nelson.[5]

“Let’s hear it again, Joe,” I requested, having grabbed my Snoopy Cap when I woke up and realized something interesting had happened.

[Snoopy Cap, a brown & white fabric helmet which contained a comm headset. The center portion was made from a white elastic Lycra fabric and the sides containing the earphones, a dark, usually dark brown, Teflon fabric. The official NASA designation was the rarely used “Communications Carrier Assembly” (CCA). The name “Snoopy”, of course, was that of Charlie Brown’s dog from Charles Schulz’s Peanuts cartoon strip. It came into use in the U.S. space program because of Snoopy’s helmet, goggles, and muffler when he was emulating a WWI pilot chasing after the ‘Red Baron’ while flying his Sopwith Camel doghouse.[6] Snoopy is also the symbol of the “Silver Snoopy Awards” originally given by Apollo astronauts in recognition of quality in the contractor workforce.]

“Are you serious?”

“Well, I just got on a headset. You never had a chance to wake me up before,” I kidded.

“It’s coming at you, America.” And the “City of New Orleans” made its way to the Moon for the second time. Unlike modern country music, Classic Country Music consists of words that tell a story and music with roots in the immigrant settlers throughout the rural South. Similarly, Classic Western Music, significantly different from Country, finds its origins in those same immigrant settlers who left the South and East after the Civil War. Western Music tells the stories of the American West, primarily about its growing ranching culture. Themes involving travel, trains, horses and cowboys, particularly, play a prominent role in Country and Western themes; thus, “City of New Orleans” seemed a most appropriate choice for a trip to the Moon. My enjoyment of both styles of music, along with that of the classical instrumental and operatic composers, came from broad exposure outside and inside my family as I grew up in Southwestern New Mexico.

“How about that,” Allen asked.

“Thank you, Joe. That’s great! We’re moving on,” I added, now referring to a famous Hank Snow[7] country song, “The Golden Rocket.”

“Don’t you know!?”

Recognizing my reference to “The Golden Rocket,” Evans said, “And a big eight-wheeler,” referring to another line from the same song.

“And, America, you’re ten minutes from LOS, and the spacecraft looks great.” LOS, or Loss of Signal, referred to that unique aspect of space travel when a planetary body comes between a spacecraft and a radio transmitter/receiver on Earth. It did not take long for crews to get used to this real as well as symbolic pulse of life in the two-hour lunar orbits.

“Okay, Joe,” I acknowledged. “That’s good to hear. And we are starting to move, now, and we’ll be ready for you when we come around.”

“All righty.”

“How long are you with us this morning?”

“Oh, not too many more minutes.”

“Hope we didn’t keep you up last night.”

“The pleasure was ours, Jack. We devoted our eight hours to selecting your wakeup call this morning and got a little help from the newsroom pool on that suggestion.”

“Well, it was a good suggestion. I had forgotten all about that song. That’s a good one! …You ought to find ‘The Golden Rocket’ for us some morning.”

“You’ll wish you hadn’t asked.” I had brought a cassette tape of country music along for the flight that included many of my favorite artists, such as Slim Whitman, Kris Kristofferson and Hank Snow, so I was not lacking for entertainment.

A minute later, Allen called with, “Seventeen, this is Houston. You’ll be pleased to hear that the IR (Infrared Camera) in the SIM-Bay is returning some beautiful data to us here.”

Evans perked up and said, “Hey; great, Joe! That’s good to hear, by gosh!”

I asked, “What are you learning, Joe?” The IR Camera[8] senses differences in the amount of heat radiated in invisible infrared wavelengths from features with different temperatures such as boulders versus fine-grained lunar soil.

“Hotspots on the Moon, Jack.”

“Well, we know we had one going around it,” referring to America and Challenger. “We didn’t know we had any on it. …Where are your big anomalies, Joe? Can you summarize quickly?”

“Jack, we’ll get that for you next pass.” The IR data included the expected heat anomalies from areas of boulder concentrations and possibly from any active, but unlikely volcanic centers. Our orbits, however, would not carry the IR sensor over any of the areas, such as Aristarchus, where photographic evidence existed of relatively young volcanic activity.

“Well, don’t worry about it. I think we’re going to have a lot of things on our mind the next pass. …But we’re just passing over Orientale again, Joe, and in Earthlight, it’s probably one of the most spectacular sights in nature!”

“Copy that, Jack. I can imagine.”

“Joe, can you imagine waking up anywhere else?” The Orientale Basin formed as the last of the large basin-forming impacts on the Moon. Lunar Orbiter photographs taken in the late 1960s show a variety of relationships between its major features that supported this estimate of age.[9] Orientale’s jagged, concentric mountain rings stood out beautifully in the strong, blue, light bathing their Earth-facing slopes, further accented by the dark mare plains filling low areas on the basin floor.

“Seventeen, we’ll think about that until you go LOS…about 30 seconds to LOS. We’ll see you on the other side. It’s going to be a good day.”

“Righto, Joe!” Allen, one of the second group of scientist astronauts, and I had spent a lot of time together when I trained on the Apollo 15 Backup Crew. He had served as the support crewmember that coordinated that mission’s lunar surface science. He also was CapCom for the lunar surface EVAs conducted by Dave Scott and Jim Irwin. A theoretical physicist by education and profession, he and I shared comparable, irreverent views of the NASA world as well as a typical, somewhat nerdy and cutting approach to kidding each other.

Once communications with Mission Control ceased as we went around the edge of the Moon and lost our view of Earth, I began to compile the crew food and sleep reports for the preceding period as well as reminding all of us that the Flight Plan called for a “urine collection period” until we began to get into the pressure suits prior to Undocking for our trip with Challenger into the valley of Taurus-Littrow. I also wanted to know if Cernan was well rested for the long and challenging day ahead.

Gene, how did you sleep?”

Oh, about six and a half hours – pretty good.”

Sleeping all right?” I probed.


How much water did you have yesterday?” Not drinking enough water plagued all Apollo missions, partly because the body was trying to get rid of about 10-15% of blood volume.

I only had three of them (containers).”

And a PRD when you get a moment.”

Okay. PRD is 36…”

After finishing recording our food, personal radiation dose (PRD), and water intake reports for the preceding day, we continued to eat breakfast and talk through some of the issues associated with suiting-up for Powered Descent and Landing. Cernan, unfortunately, also still had enough discomfort from intestinal gas to complain about it.

During breakfast, I had a chance to re-examine the floors of craters around Aitken and made some summary observations in response to a question from Evans: “Well, I think they’ve been filled with something, Ron. …There’s been a molten lake on [the floor of] some of those new ones, I guarantee you. Yes, there seems to be…four kinds of crater fill that I see. There’s a very smooth, light-colored stuff. …There’s old Aitken, again [by the way]. …And then there’s a variety of irregular surfaces – the turtleback [and] domical fillings that seem to be pretty old, and the mare fillings that may be associated [in time] with that stuff [the turtleback and domical fillings]. [They] may be contemporaneous like here in Aitken [where] you see them together and it’s hard to say one’s early or later [than the other]. And then there’s that kind of stuff Gene was talking about [earlier] – that’s just in smaller craters [as fill], things that [appear to slump or be impact melt] in the floors.”

Our hodgepodge breakfast continued, with emphasis on fluids, particularly juices. At one point, I said, “It’s the only way I can drink a lot of water is to drink these juices. Since I left New Mexico, I just haven’t been able to drink much water.” I grew up with untreated water from a deep well in limestone and had never become accustomed to chlorinated water.

We also discussed how to deal with managing the un-stowing of our pressure suits and the temporary stowage of the Probe and Drogue from the tunnel to the Challenger so they would be out of our way. In the limited volume of America, these large items took a lot of the remaining space. Training in the CSM mockups never covered all the permutations imposed by weightlessness. We decided that it probably would work best to put the suits on and then deal with the Probe and Drogue stowage. We also each filled a water bag and installed one in our suit along with a fruit stick. Once helmets were locked in place, both the nipple on the bag and the fruit stick would be accessible to our mouths near the neck ring. On the lunar surface and suited for work outside the Challenger, these would give us the only water and nourishment we would have for about eight hours.

Other stowage had to be put in order and at one point I commented to Evans: “Let’s see, I’ve got what – three fecal bags in there (a jettison bag) now? And I think I can recognize them but I can’t remember to label those darn things. It’s such an ordeal [to have a bowel movement. …Let’s try [a] process of ‘elimination’ – you guys recognize yours and what’s left is mine.” Ah, the joys of camping in space!

Cernan continued to worry about his intestinal gas problem, prompting me to say, “Hope that gas of your clears up. Got too much to [do down there in] one-sixth [gravity]. I’m sure I speak for you also when I say that, heh, heh – nothing like getting all this free sympathy. Doesn’t help you one bit.”

Meanwhile, getting back to the Timeline, I asked Evans, “…Okay, you got that Ron? LOGIC POWER [circuit breakers]? Two of them off? …Yes, [two]. …IR’s coming OFF. …Yes, [OFF]. And give me a ‘verify’.”

That’s verified.”

“Now I need the IR and UV (ultraviolet camera) covers CLOSED and the UV OFF.”

“That’s verified.”

How come we didn’t leave that [IR camera] on all night?” Cernan wondered. “Oh, the Sun, possibly,” responding to Evans or me. “All right, gang, we’ll wait for AOS and, as soon as everybody’s through eating, we can go to work.”

Ron, we need to enable all the [(Reaction Control System) RCS] jets before (Acquisition of Signal) AOS.” (Readers may also query the glossary in the ALSJ for most acronyms used in this chapter.)

Got it,” Evans replied.

How about if we check the tunnel pressure?” I suggested, trying to get ahead in the timeline.

Yes, you can do that,” Evans agreed. Go through the normal 20.4 [procedure]. …There’s a decal up there for CM/LM pressurization. …You don’t have to do much. …Do you want to save this coffee? …See what’s coming up here. …Okay, then we get in…the LCGs (Liquid Cooled Garments). …We’ve [already] capped our [biomedical] transducers. Have you done that, Geno?”

[Basically, the LCG consisted of long-handled underwear through the fabric of which ran interconnected tubes that could circulate cool water on demand. The LCG constituted one of the most critical enabling technologies for lunar exploration. Without it, air-cooling would have been totally inadequate for removing the body heat load generated by working in a pressure suit. The biomedical transducers to which Evans referred were stuck to our chests at places identified previously by four small spot tattoos on the skin, indicating where heart rate and respiration could be sensed. The transducers needed to have electrical clamps or “caps” attached to pick up the faint electrical currents they sensed. These one-inch diameter adhesive transducers significantly irritated and inflamed our skin and, needless to say, were not very popular. One more complaint to be directed at the flight surgeons after we returned home.]

Did you get your transducers capped, Ron?” Cernan asked.

No, I am not on biomed today.”

He doesn’t have any on?” I asked from the tunnel. “Okay. …[Delta-p is] 0.5 now. …Well, it’s not there [less than 0.2], but that’s because it (Challenger) rides low [in pressure]. Should be, yes. …Gene, you want to…”

Check DIRECT O2?” I wanted to be sure that no oxygen was bleeding into the cabin that would cause this small difference in pressure.

Yes. DIRECT O2 is OFF,” referring to the CM/LM pressurization decal in the tunnel.

As AOS approached and the start of our tenth lunar front-side pass, we had already filled water bags for our suits, configured SIM-Bay instrument switches, folded the couches for maximum room to maneuver as we suited up, and generally got ready to move into our LM ACTIVATION checklist. This did not leave any time to look at the illuminated features below our orbital path. That would have to wait until I returned from Taurus-Littrow.

At AOS, I picked up the conversation with CAPCOM Gordon Fullerton in Mission Control. Gerry Griffin, our lead Flight Director, had taken over that overall position of responsibility in the MOCR for landing day and his Gold[10] team of Controllers sat at their various consoles.

“Okay, Houston. We’re with you and we’re in the process of getting the tunnel pressurized and moving right towards Probe and Drogue removal.”

“Okay, Jack. Good morning.”

“Good morning, Gordy. Welcome aboard! …I take it you’re going to pick up the post-sleep reports later. Is that correct? From Ron?”

“Any way it’s convenient to you.”

“Well, we’re moving towards getting the [pressure] suits on. Unless you want me to take 5 minutes here, we’ll leave it alone and let Ron give it to you. …Everybody ate and drank and slept just about like last night.”

With that, I left communications with Fullerton to Cernan and Evans and began to work my way into the pressure suit. Actually, this was not too difficult in weightlessness. The one piece suit, except for helmet and gloves, consisted of an inside rubber pressure bladder, seven layers of aluminized Mylar for insulation, and a white beta-cloth outer cover for Sun reflection and micro-meteor protection. A long zipper ran diagonally across the front torso from inside my left shoulder at the helmet ring down to the left hip, above the waist joint. The zipper opening allowed me to put my legs well down into the suit legs, then work my right arm into its suit arm, followed by my head through the helmet ring, and then my left arm into its suit arm. It always helped to have someone else zip the airtight zipper, but it also could be done unassisted.

“Good morning, Gordy,” Cernan called.

“The Tunnel Hatch is out,” reported Evans.

“Gordy, how does America look to you this morning?” Cernan asked.

“Beautiful, as it has all the way to date.” It was never clear to me why Cernan kept asking this type of question. I personally was certain that we would be told if there was anything out of the ordinary with respect to spacecraft systems or its environmental control.

“The old Probe is underneath the couch,” Evans interjected and then asked about me, “How are Jack’s EKGs and stuff (respiration)? …Wait a minute…heh, heh. …He’s not plugged in. But, you know, he’s had them on all night. Were they good?”

“Yes, Ron. He was plugged in; we had good signals. …If someone’s near the telemetry switch, [and] if you go to ACCEPT, we’ll give you a state vector.” Having a switch in the both spacecraft by which the crew had to enable the uplink of telemetry into the PINGS added an important element of communications and computer discipline. Indeed, it added security from any unauthorized entry of data into our computer. In this specific case, Mission Control wanted to give America’s guidance system their latest determination of our three-vector position and velocity in space at a specific time. Three sources of information contributed to this state vector for America and Challenger: Evans’ P52 sightings on navigation stars, subsequent velocity tracking using Doppler frequency changes in our downlink communications signal, and computer models of the lunar gravity field.

“You have ACCEPT,” Evans reported.

“And,” added Fullerton, “…we’re supposed to update [you on] your trajectory, which is looking good – predicted perilune at PDI (Powered Descent Initiation) without DOI-2 – would be 11.9 nm, a little lower [than planned]. So that means that DOI-2 will be a little less, in terms of DELTA-V, than nominal. But, otherwise, looking good.” DOI-2 (Decent Orbit Insertion-2) would be a small RCS burn by Challenger over the lunar far side after undocking and after Evans had completed raising his orbit (Circularization burn). DOI-2 would result in our altitude over the landing site being lowered to about 7 nm and further minimizing the propellant needed for Powered Descent to the landing site. Without DOI-2, our predicted PDI ignition altitude (also at perilune) would be the 11.9 nm Fullerton mentioned.

After Evans repeated this information to Cernan and me as we worked into our suits, Fullerton said, “Okay. I have your [state] vector [in] now. You can go back to BLOCK [on the telemetry switch].”

“Okay, we’ll go to BLOCK.”

America, Houston. You owe us a re-verification of docking tunnel index angle.”

“…it hasn’t moved,” Evans answered, “– plus 1.2.”

“Okay, plus 1.2,” Fullerton read back. “For your information, Ron, on consumables this morning, we’re running six percent above (less usage than expected) the Flight Plan line on RCS. On the hydrogen, we’re about eight percent above the line on Tank 2; right on the lines on the other two hydrogen tanks. And on O2, we’re running our standard four to five percent below the line on oxygen Tank 1; Tank 2 is right on; and Tank 3 has now gained to about three percent above the line. All looking good.”

“Okay, Houston. Hey, that’s mighty fine!” said Evans, speaking as a true Kansan.

Evans then began to catch up on the medical and food reports as Cernan and I were taking up almost all the cabin with our suiting activity. Ron would get into his suit by himself after we had entered the Challenger. Being in a suit and protected against a depressurization anomaly constituted a requirement for undocking.

“Okay. I’ll give you the Commander’s food from yesterday…Four bacon squares, cornflakes, orange beverage, two sips of coffee, a vitamin [for breakfast]. …Meal B (lunch): chicken and rice soup, meatballs and sauce, orange PA drink, and one caramel stick. Meal C (dinner): potato soup, beef and gravy, citrus beverage, a chocolate bar, a package of pecans. …Commander’s medical log: PRD 17036, six and a half hours of good sleep, one Seconal last night, three bags of water. …For the Commander [for breakfast] on Day 5 (today): spiced oat cereal, sausage patties, instant breakfast, and vitamins.

“Here we go on the LMP’s food. Two bacon squares, scrambled eggs, two apricots, cocoa, and a coffee. Meal B: fruitcake, citrus beverage, hamburger, and coffee. Meal C: lemonade, beef and gravy, ambrosia, cereal bar, and tea, …[Today], it’s a sausage patty for LMP – sausage patties, cinnamon-toasted bread, instant breakfast, coffee with K, and a grape drink, and a vitamin. …For the LMP’s medical log: PRD 24108, seven and one-fourth hours very good sleep, one Seconal last night, three and one-half cans of water.”

“We’re ready to go on [to the] Command Module Pilot of the Spaceship America and his menu,” said Fullerton.

“Okay. Bacon squares, scrambled eggs, cornflakes, orange juice, two coffees, three caramel candies…three vitamins – that’s three sticks of caramel candy [for breakfast]. Meal B: chicken and rice, meatballs, butterscotch pudding, orange PA drink. …Meal C: potato soup, beef and gravy, chicken stew, orange GF drink, tea, chocolate bar, and a package of pecans. …CMP medical log: PRD 15034, and about five and a half hours of good sleep – a little trouble getting to sleep last night, and I woke up early this morning. I took a Seconal; didn’t seem to have much good. And I had four cans of water. …I think I was on the biomed all the time last night, too, so you can check out that sleep.”

Challenger Wakes Up: Power and Environmental Control

Evans and Fullerton then modified some burn constants in the CSM’s PINGS computer’s memory, during which Evans commented, “The LMP has got his suit on. They’re connecting up the LCG (Liquid Cooled Garment) water connection, and he’s still unzipped.”

Ten minutes later I had finished suiting up except for a helmet and had moved through the tunnel to the Challenger’s hatch with my CSM communications, oxygen and cooling water umbilical trailing behind. I called, “Houston, how do you read the LMP?”

“LMP, you’re loud and clear.”

[The Grumman Aircraft Corporation in Bethpage, Long Island, New York, manufactured Challenger as the last Lunar Module, LM-12, for a lunar mission. Later, Grumman would use a Descent Stage structure for the Skylab Apollo Telescope Mount to which would be attached the solar telescopes used on the three Skylab missions. In November 1962, Grumman had won the competition to design and build the lunar lander for the Apollo Program. This occurred about a year after North American Aviation had won the competition for the Command and Service Module (often referred to as the “Apollo Spacecraft”).[11] In addition to the work of Grumman engineers and builders, NASA’s Apollo Spacecraft Program Office’s engineers, led by Owen Maynard and then Owen Morris, contributed a parallel design effort, followed by a Block II upgrade for use on Apollos 15-17, that continually helped refine the detailed configuration, manufacturing and testing of this remarkable spacecraft. This process of iterative interaction on design continued until the Critical Design Review (CDR) when the design went under Configuration Control. After that, design changes had to be approved by and coordinated through George Low’s Configuration Control Board (CCB) so that the impacts of any changes on other systems could be fully vetted by all concerned. Challenger was the last of three upgraded or Block II Lunar Modules that had the consumables and propulsion capability to support a full three days on the Moon and three, seven to eight hour exploration periods outside the spacecraft.

Because of the long-range vision of Low, creation of Block II Lunar Modules began in February 1969, over five months before Neil Armstrong made his first steps on the Moon.[12] Under the direction of Apollo 9 Commander Jim McDivitt, working for Low as Manager of the Apollo Exploration Office, Grumman and NASA took several hardware and operational steps to permit more stay-time and land more payload on the Moon than previously planned. They extended the Lunar Module Descent Engine nozzle by 25.4 cm to gain more thrust. Propellant, oxygen and water tanks also were enlarged. Operationally, the CSM performed the initial Descent Orbit Insertion (DOI-1) by reducing the altitude of perilune over a landing site to about 10 nm (11.9 nm in our case). The net effect of these combined hardware and operational changes increased landed payload by ~1200 kg. Science-related payload increased from 214 kg on Apollo 14 to 545 on Apollo 15.[13] The additional payload also included the additional consumables necessary to support three, ~7.5-hour periods of extravehicular activity (EVA) versus two, ~4.5-hour EVAs on Apollo 14. An up-rated pressure suit (A7L-B) could be recharged with oxygen, cooling water, and battery and would allow up to eight hours for surface exploration each day. Ultimately, added scientific pay-load, such as the Lunar Rover, limited the stay-time to three days versus the possible four days; however, to the credit of Grumman and NASA engineers, this Block II Lunar Module, when combined with a lower altitude for the start of powered descent, matched the plans for four days on the Moon envisioned in the original Design Reference Mission that Joe Shea had required of Grumman and North American in 1967[14].]

After activating the CABIN DUMP VALVE[15] on the hatch to equalize pressures between the two spacecraft, I said, “Gordy, I’m opening the hatch…[Docking] Index…1.2.”

Fig. 8.1. The docking hatch in closed position seen from inside LM-12 during pre-launch closeout procedures by Grumman. LM-12 was christened “Challenger” by the crew.[16] (NASA negatives provided by the Northrup Grumman History Center scanned by Paul Fjeld[17]).


On this third entry into the Challenger, I again noticed a peculiar, temporary sense of disorientation. This went away instantly as soon as I looked at the familiar shape and configuration of the front panels of the cabin. I suspect that this brief disorientation was a consequence of training standing up in the Lunar Module Simulator while, in contrast, training lying down in the Command Module Simulator. Hundreds of hours in each position, differing by 90 degrees in Earth’s gravity field, had imprinted two different visual orientations on my brain that briefly were in conflict.

Fig. 8.2. The author as Lunar Module Pilot (LMP) in LMS-2 during training at the Kennedy Space Center (LMS-1 was in Houston). In addition to the main control panels at the front, note the 16 mm Data Acquisition Camera (DAC) with white side plate in the LMP window to the left of my head. Above my shoulder is a bank of circuit breakers and other switches along adjacent panels. Similar banks of switches are located next to the CDR position at left. (NASA Photo KSC-72PC-0539).

Fig. 8.3a. A general schematic of the interior of the LM facing forward in the crew compartment, showing the locations of various instrument panels and other elements. (Apollo News Reference Lunar Module Quick Reference Data[18]).

Fig. 8.3b. The front panels of LM-12 (CDR panel 1 to the left; LMP panel 2 to the right; and panel 3 angled at the bottom). At center top is the AOT (Alignment Optical Telescope) surrounded by brace bars. The black fiberboard light shades or glare shields at left and right were later replaced before launch with ones having Velcro fasteners. They prevented instrument lighting from reflecting onto the windows. (NASA/ALSJ/Paul Fjeld).

Fig. 8.4. A closer look at panel 4 and the DSKY (or DISKEY, display & keyboard, pronounced ‘dis-key’) in LM-12. Program, verb, and noun data numbers were entered from the keyboard and displayed in the rectangular screen above. The Commander’s (CDR) attitude controller is the gray handle to the left of the DISKEY. The yellow, rubber covered, forward-leaning rods on either side of panel 5 at left (and a similar set for the LMP on panel 6) were hand-holds for balance in zero gravity since the astronauts were not seated, but rather stood in front of the control panels held in position by cable restraints from the side panels and hooked to each side of their suits and attached under the front console (see Fig. 8.3a↑). (NASA/ALSJ/Paul Fjeld).

As I floated through the tunnel into the Challenger Evans commented, “Okay, Houston, I’m going to skip the P52 (realignment of the PINGS Inertial Measuring Unit) for a while and maneuver to the…undock attitude…”

“Roger. Stand by on that one, Ron.”

“Wilco (will comply).”

“We want to be sure we can get some…good stars [for you to see] in the undock attitude, …and if there’s no reason why not, we’d just as soon you go ahead and do the P52 now. Finish that off and then start the maneuver.”

“Okay. The big reason [to wait] is that Gene’s getting into his suit right now [in the LEB]. …As soon as he gets out and gets in his suit, well, I’ll do a P52 maneuver.” In the LEB (Lower Equipment Bay) area, Cernan blocked access to the Sextant and PINGS DISKEY normally available there for performing the P52 star sighting alignment of the guidance platform.

“Okay…Ron. Can you give us AUTO on the High Gain [S-Band antenna]?”

“Okay. Just a second, Houston.”

Until the Challenger’s communication systems came on line, I would be using the communications umbilical through America. After removing the Challenger’s window shades to let in some sunlight, I reported, “We’re transferring to LM POWER, Houston”. Going to Lunar Module Power required closing two, Electrical Power System’s (EPS) XLUNAR BUS TIE circuit breakers, thus connecting the Descent Stage batteries to Challenger’s main electrical bus. This resulted in floodlights blinking and the illumination of the yellow PWR caution light of the Caution and Warning display on the front panel.

[Four, fully charged, Descent Stage batteries powered Challenger’s EPS at this point. For Lunar Module power, Grumman and NASA originally planned to use fuel cells, like those powering America from its Service Module. Given early uncertainties in fuel cell development and after evaluations by Owen Maynard at NASA and Tom Kelly at Grumman, batteries eventually replaced fuel cells in the Lunar Module design because of their greater “reliability and operational simplicity” in spite of a weight penalty of some two hundred pounds. The Descent Stage batteries had silver and zinc electrodes immersed in a liquid potassium hydroxide electrolyte and provided a high power density of three ampere-hours per pound. Less power-dense versions of these Eagle Pitcher batteries, at two and a half ampere-hours per pound, would power the Ascent Stage when we left the Moon or encountered some Abort situation requiring sole use of that Stage. The batteries had experienced a difficult development and manufacturing history at Eagle Pitcher; but close attention by Kelly and other Grumman engineers finally overcame early problems in meeting qualification standards in time for Apollo 9, the first flight test of Lunar Module LM-3, the Spider, by Jim McDivitt and Rusty Schweikart.[19]]

“Okay; OFF, RESET, back to OFF,” Evans reported as he performed his part of the power transfer procedure that stopped America’s electricity from powering some of Challenger’s essential heaters.

“We have LM POWER,” I confirmed.

“That was [at] 107:49:28 [ground elapsed time],” Evans stated. Knowing this time, Dick Thorson at the LM CONTROL Console in the MOCR could track Challenger’s power usage.

Then I turned on the floodlights, opened valves to the Descent Stage water and oxygen supplies, and put CABIN REPRESS to automatic and closed the Environmental Control System’s (ECS) CABIN REPRESS circuit breaker. Challenger could now supply its oxygen to the cabin if needed.

[As in the case of the Command and Service Module, the Challenger’s ECS had been developed and manufactured by Hamilton Standard, but significantly modified in the course of solving the overweight problems faced by the Lunar Module in 1965. We ended up with a high-pressure (2,730 psi) oxygen supply tank in the Descent Stage, and, smaller, low-pressure tanks in the Ascent Stage.[20] Piping, valves, check valves, and fans (pumps) could be configured to supply oxygen either directly to the cabin or, through the suit loop, to the normally un-pressurized suits we would wear for safety during undocking, descent, landing and ascent. If the cabin became partially or completely depressurized during these dynamic events, the system would maintain pressure and oxygen flow to the suits. Cabin and suit air circulated through a replaceable Lithium Hydroxide (LiOH) canister to remove respiratory carbon dioxide and filter out any particles introduced into the cabin, such as lunar dust.]

“LM WATER is OPEN, and O2 is OPEN,” I reported.

[Freezing and sublimation (solid state evaporation) of this water by exposure to space vacuum through a porous plug cooled Challenger’s cooling water subsystem. This cold water, through a heat exchanger, cooled the water-glycol circuit that, in turn, cooled electronics, suit oxygen, and the water that flowed through our water-cooled underwear.]

I systematically continued to work through the LM Activation Checklist. First, I activated and configured the electrical power system so that we could monitor and control power from the four batteries in the Descent Stage and power the direct current (DC) to alternating current (AC) inverters needed to give the AC required to operate the Challenger’s displays and controls. Then I told Fullerton, “…I’m going off of CSM Comm, and I’ll be coming at you before long on S-BAND, if I can.”

“Okay,” acknowledged Fullerton, and I disconnected my line back to America and attached the Challenger’s communications line to my suit Electrical Connector. Then, I began to set the 15 switches and circuit breakers needed to activate and control direct S-Band communications with Mission Control at the next AOS.

Meanwhile, back in America, Evans was preparing for our eventual undocking. “Ron, Houston. We’ve taken a look at stars available in the undock attitude, and they don’t look too good. We suggest you use the present attitude for your [P]52 and then maneuver. Over.”

“I’m just about to get Gene out of the way here, and then I will.”

“Okay, and we’re less than 3 minutes to LOS (Loss of Signal) now,” Fullerton replied. “So when you finish that [P]52, we’d like you to copy down the NOUN 5 and [NOUN] 93s for us.”

“Will do.”

[The Flight Plan called for these readouts to be copied, but reminding us to do necessary things constituted one of the valuable contributions of Mission Control. NOUN 5 gave the angular difference in star position from that predicted from the last alignment. NOUN 93 displayed the required angular change in “torquing” angles to re-align the gyroscopes to be consistent with the new star sightings. Evans, however, was running about 20 minutes behind due to our suiting up activities in the Lower Equipment Bay (LEB). With a looming loss of communications, Will Presley and Jonny Ferguson manning the GUIDO (Guidance Officer, pronounced: ‘guy-dough’) Console in Mission Control just wanted to be sure Evans remembered to record the alignment data, as GUIDO would not have telemetry to see it directly. These numbers would provide a good indication on how well the guidance system had performed, so far.]

America, Houston. About 1 minute to LOS. Nothing further for you. We’ll see you on the other side.”

“Okay, Gordo. We’re hustling like heck. We might make it!”


Cernan joined me in Challenger’s cabin with our helmets, gloves and numerous checklists as we lost communications with Fullerton. We both attached the cable restraints that would hold us in position on the Challenger’s floor while we worked (Fig. 8.3a↑, cables at sides of compartment).

[These restraints put us in the same physical position in which we stood during all our training in the Lunar Module Simulators. Standing rather than sitting in the Lunar Module provided each of the crew head mobility that gives an excellent range of view out the small, inwardly sloped, triangular windows in front of each position. Standing also gave greater arm reach than sitting. Adopted early in the maturation of Grumman’s winning design for the Lunar Module, this innovation over traditional seating greatly reduced the weight and structural complexity of seats.[21]]

In addition to setting EPS and communications related circuit breakers on Panel 11 just above his left shoulder, Cernan asked Evans for a time hack in order to activate Challenger’s Mission Timer and be consistent with America’s.

Fig. 8.5. The circuit breaker panel 11 in LM-12 above the CDR’s left shoulder. Breakers with white dots indicate those that should be open prior to EVAs. (NASA/ALSJ/Paul Fjeld).

…coming up on 108:12 in 20 seconds. Set it 108:12:15…30 seconds from now. Set it for 15 [seconds because] I missed it [the first time]. Okay, 10, 11…28, 29, Mark!”

While Cernan and Evans synchronized Challenger’s Mission Timer with America’s, and following a checkout of the Caution and Warning system. I moved in to provide cooling by activation of the Primary Glycol Loop. Activation of the Environmental Control System overall went smoothly, enabling us to connect our suits to the Challenger’s oxygen and coldwater hoses, the latter feeding cooling into our water-cooled underwear. The oxygen hose from America that I had been using went back for Evans to stow in America, awaiting my return from Taurus-Littrow.

I recorded the time of activation of the cooling water flow to the sublimator so that Mission Control could model water usage based on various pre-mission equipment tests and the real-time temperature data they would have from our telemetry. Next, we each went across the rows of circuit breakers, five rows on Cernan’s Panel 11 (Fig. 8.5↑) and four on my Panel 16 (Fig. 8.2↑; also see Fig. 8.6 below), configuring them, according to diagrams in the Activation Checklist, for a full power-up of Challenger into an operational Moon landing craft.

Fig. 8.6. The panel 16 circuit breakers above the LMP’s right shoulder in LM-12. Breakers with white dots indicate those that should be open prior to EVAs. The yellow tape strip with black bars on the top row encloses the four quad thruster switches of the Reaction Control System (RCS). The white arrow in the third row marks the Glycol Pump Secondary circuit breaker referred to later in text. (Base photo NASA/ALSJ/Paul Fjeld).

With all of Challenger’s systems now having access to power, Cernan activated the heaters in our attitude control thrusters, part of the Reaction Control System (RCS). Activation and checkout of this essential system would take place when thrusters had warmed sufficiently and we were in communication with Mission Control. As Cernan turned on the RCS heaters, I rapidly cycled the circuit breaker for the Caution and Warning (CW) instrumentation to make sure that the CW display correctly indicated that the regulators for the separate A and B fuel and oxidizer flow paths were still closed. We would open those propellant paths to the thrusters prior to undocking from America and after the thruster temperatures had time to stabilize.

Computer, Guidance, and Communications

Turning on Challenger’s Primary Guidance and Navigation System (PGNS, pronounced “PINGS”), and making the entries into the Display and Keyboard (DSKY, pronounced “dis-key”, Fig. 8.4↑– both PGNS and DSKY will usually be spelled PINGS and DISKEY here as used conversationally) necessary for its self-test routine next occupied Cernan while I called out and monitored his entries using the checklist.

[A properly functioning PINGS was essential to landing on the Moon. It’s three, precisely perpendicular, very low friction gyroscopes would provide a stable, star-based reference in space that the PINGS computer would use to measure changes in velocity along three perpendicular axes that, in turn, would define changes in our position in space relative to the stars. Along with Mission Control’s highly precise tracking of our line-of-site velocity using small, velocity dependent frequency variations in our radio signal (Doppler effect), these data would be used to guide Challenger to a point in space a few hundred feet above the surface of Taurus-Littrow from which a safe, piloted landing would be possible.

The PINGS had its origins at Massachusetts Institute of Technology (MIT) in the 1950s with the development of guidance systems for the Navy’s submarine-launched, Polaris intercontinental ballistic missile program and in designs for automated interplanetary probes.[22] MIT’s Instrumentation Laboratory, under the direction of Dr. Charles Stark Draper, designed these revolutionary computer controlled guidance systems. In 1960, with George Low of NASA’s Space Task Group beginning to think seriously about human flights that would orbit the Moon,[23] the Laboratory’s Richard Battin concluded that an onboard, gyro-based guidance system could be developed for human spaceflight. This system would include the incorporation of periodic updates from sightings of stars and a new statistical technique for vehicle control called the “Kalman filter”, named after its inventor, Rudolf E. Kalman.

Through the initiative and efforts of the Space Task Group’s Robert Chilton, the Instrumentation Laboratory received a sole source contract in August 1961 to develop what would become the PINGS. This contract was let only two months after Kennedy issued his challenge to go to the Moon and literally was the first major contract in the Apollo Program. The estimated cost for PINGS development was $4.375 million (1962 dollars); but the effort ultimately required about $100 million by the time the PINGS guided Apollo 11 to Tranquility Base in 1969. Although many costly details had to be added to the proposed design, its basic conceptual elements remained constant: a versatile digital computer; an optical sextant for navigational star and lunar landmark sightings; an inertial, gyroscope and accelerometer-based guidance platform; a display and keyboard unit to interface with the astronauts; and a variety of supporting electronics. At the time of the contract, no specifications yet existed for how accurate the system had to be; however, that would be determined as more became known about the Moon and Apollo spacecraft performance. Nonetheless, the final product, its computer built by Raytheon and the guidance unit built by Honeywell, performed magnificently and would guide both America to the Moon and permit Challenger to land in a narrow lunar valley.]

For Cernan and me, preparing for the final Apollo lunar landing, not all of the sequence of indications related to the PINGS self-test came up as expected. After writing down those differences, we decided to press on with the Activation Checklist and discuss the self-check anomalies with Mission Control when we again had contact. At this point, I went to work to verify the correct indications of the “TalkBacks” for various mechanical systems. These systems included vents, landing gear, regulators, and the like. These TalkBacks showed either grey or barber pole indications in small windows that indicated the OPEN or CLOSED and DEPLOYED or NOT DEPLOYED positions, respectively.

Meanwhile, sometimes speaking in the third person and sometimes to Cernan calling through the tunnel, Evans began to talk himself through suiting up and taking star sightings for the P52 we would need for both spacecraft before Undocking. “I can’t find any stars. …Yes, ‘we’re’ upside down in the wrong attitude. …I can’t find any stars [in this attitude]. …‘We’re’ finally going to maneuver to the [right P52] attitude. …Well, ‘we’ don’t have our suit on yet, but ‘we’ finally got an alignment [to Challenger]. …‘We’re’ moving to attitude…” Cernan and Evans then began a conversation something like this:

“How soon will you be at attitude?” Cernan yelled through the tunnel.

It’ll be awhile, yet. If you want to, I’ll go ahead [and suit up]. I can put my suit on at the same time.”

“Go ahead.”

Okay, let me get my suit on real quick-like.”

“Are you about suited up, Ron?” Cernan called a few minutes later.

Yes. …You need to get to attitude faster, [Gene]?”


…Okay…What the heck is that…noise up there!”

“Jack’s activating the ECS and it’s noisy. …Can you give me your times for a LGC/CMC (LM Guidance Computer/Command Module Computer) CLOCK SYNC AND T-EPHEMERIS UPDATE?” The LGC/CMC, of course, needed to have their clocks exactly synchronized.

[The “T-Ephemeris Update” refers to updating the computer clocks to a uniform time scale established in 1952. To provide a uniform and more accurate standard for time comparisons, the astronomy and guidance communities substituted a reference to the Earth’s orbit around the Sun for a previous reference to the Earth’s rotation.]

…I can give you that now…T-EPHEMERIS IS 108:31:27.69.”

As Cernan and Evans brought Challenger’s computer clock into harmony with America’s, I checked out our suit fans and water separation subsystems and verified the proper function of the glycol cooling loop activated earlier. With that done, I tackled getting the S-Band, long distance communication system up and running. This was never a certain task, involving activating and positioning a Steerable Antenna and getting the gage indications of uplink signal strength as high as possible.

Once the clock coordination took place, Cernan set up the Digital Auto Pilot (DAP) through a VERB 48 entry in to the PINGS.

[The DAP[24] grew out of a Minneapolis-Honeywell analog control system that had been used in both the Mercury and Gemini programs. Cline Frasier and Clifford Duncan from Joe Shea’s Apollo Spacecraft Program Office, however, made the decision in 1964 to integrate the autopilot with digital control from the PINGS computer, eliminating the complexity of another computer beyond the PINGS and the Abort Guidance System (AGS) that I would activate in due course. This meant that hand controller inputs for attitude and velocity changes would be processed through the PINGS computer which would command the appropriate RCS thruster firings, taking into account the geometry of the thruster quads and any thruster failures that might exist. With this decision, the PINGS computer included the capability to integrate manual control inputs, thruster commands, VHF ranging, star sighting updates, attitude and acceleration sensing, a variety of crew inputs, navigation and instrument panel displays, and telemetry to and from Mission Control. The DAP and a comparable system in the Command Module (the SCS, or Spacecraft Control System) constituted the first “digital fly-by-wire” control systems in an operational air or space flight vehicle.]

The entries we needed to initialize Challenger’s DAP included two codes; the weights of Challenger and America, 36,714 and 38,078 pounds, respectively, and the trim codes for Descent Engine in pitch and roll.

Challenger, this is Houston. How do you read?” Fullerton called as we came around the eastern edge of the Moon.

“Loud and clear,” I replied.

Cernan followed with, “Hello Gordy. This is Challenger. We’re reading you loud and clear.”

“Okay,” answered Fullerton. “You’re readable. Lots of background noise at the moment.”

“Okay. We’ll update you in just a minute.” Cernan and I finished relocking our restraints, positioning us in Challenger’s cabin, and then he continued, “Let me give them an E-memory dump [from the PINGS]. …Gordy, Jack will update you in just a second. And I’ve got some words for you, but I’d like to give you an E-Memory (Erasable Memory) dump as soon as you get the Steerable [S-band antenna].”

“…They got the Steerable,” I reminded Cernan. “Okay, Gordy. How do you read the LMP? This is your ‘S-BAND T[ransmit]/R[eceive] in Secondary Power Amp[lifier] Check’,” I continued as I called out the required item from the Checklist.

“Okay, LMP. You’re clear. Lots of background noise, though.”

“I’m going to bring up [the gain on] the Steerable,” and I adjusted the pitch and yaw of the antenna to optimize signal strength on its indicator dial. “Okay, Houston. How do you read, [now]?”

“You’re loud and clear, Jack.”

In the middle of this check, Cernan asked, “Do you know where our scissors are?” Remember that we only had the one pair for use on the lunar surface because Evans earlier had lost track of his pair in America and would need one of ours for opening food containers.

“Yes,” I answered, “they’re in the [Flight] Data File.”

Meanwhile, Evans, in cooperation with Mission Control and Ken Mattingly as Capcom for his separate activities, moved to complete all the tasks he had to perform all alone in preparation for undocking the Challenger from America prior to our descent into the valley of Taurus-Littrow.

“Hey, Houston, America. Man, you wouldn’t believe it. I finally got my suit on!”

“Nothing to make you feel good like a new suit of clothes,” joked Mattingly.

After giving Mission Control the results of his P52 alignment of the PINGS guidance platform, to be used later to provide an initial alignment of Challenger’s platform, Evans reported, “Okay, I removed the CSM/LM umbilicals. Guess I need to install the PROBE and DROGUE. I’ll get those things done right now.”

“All right. I’ll make a note of the [LIOH] canister [replacement] and remind you of it later.”

“Yes; okay”

“Hey, America, can you confirm that you’ve got a pair of scissors on board with you?”

Laughing at this problem of his lost scissors, Evans replied, “Yes, I made them keep one.”

“Okay. That’s good thinking.”

“They couldn’t ever find the other set, either.”

“Gets hungry without those.”

“It sure does!” Evans exclaimed, and our chow hound laughed even harder.

“We could hear your DROGUE and PROBE banging around there. It sounds like the kitchen [which] is what reminded us of it (the scissors).”

“Hey, Ron,” I called through the tunnel. “We need to check out that VHF [communications between us]. You ought to get that done before you close up [the tunnel], Ron. …Houston, we’ll be right with you. We’re going to check out our VHF. …[Ron,] Let me finish this part of it (the S-Band Steerable Antenna Activation) and then we’ll get to that [VHF check].” Turning to Cernan, I asked, “You want to read that to me, Gene, [under] the S-BAND [in the Checklist]? …I’m right here in the middle of the page.”

“Okay. S-BAND [to] PM (Phase Modulation).”


“SECONDARY,” Cernan continued, reading through the eight switch positions necessary to set up the S-BAND system fully for Powered Descent communications and telemetry while I responded and set each switch.

[Communications systems and subsystems designs for the Lunar Module resulted as a consequence of design and contract interactions during 1964[25] between the Apollo Spacecraft Program Office (ASPO), Grumman under Tom Kelly, North American under John Paup, and Radio Corporation of America (RCA) under Frank Gardiner. RCA served as a subcontractor to Grumman for electronics systems. (Separately, Dalmo-Victor provided the Steerable S-Band Antenna as a vendor to Grumman.) S-Band systems would support communications from the two spacecraft to the large antennas of the Deep Space Network (DSN) on Earth, managed by the Goddard Space Flight Center (GSFC). Shorter wavelength VHF systems would support spacecraft to spacecraft, EVA astronaut to astronaut, and EVA to spacecraft communications. VHF transmissions from an EVA astronaut to the Challenger (and, later, to the Lunar Rover) would be converted into S-Band for retransmission to Earth. Of course, full compatibility and as much commonality as possible were needed between the spacecraft and EVA systems.]

“Houston. How do you read the LM?”

“Loud and clear, Jack.” With the S-BAND fully operational, Dick Thorson and Bob Legler, sitting at the LM CONTROL console and Merlin Merritt at the LM TELEMU (Telemetry) console in Mission Control could watch over my shoulder via telemetry as the systems came on line.

“We’re in step 2 [on right side of Page 3-17] and we’re giving you your second S-BAND check. And [now] I am going to TRACK MODE – AUTO. …Okay, Houston. I can hear the antenna rumbling up there, but…I have still not peaked [on signal strength]. Still reading 3.7.”

“Okay, you’re loud and clear, Jack. It looks like a good lock [by the antenna on the uplink carrier] to us.” Fullerton would have been looking over to the LM TELEMU console for a nod from Merritt.

“I’ll leave it there, and I’m going BIOMED RIGHT.” This switch change put my biomedical data, heart rate and respiration, on the down link telemetry. “…SQUELCH is OFF. How do you read?”

“Still loud and clear,” replied Fullerton, having this time checked with the SURGEON console.


“Hello, Houston,” Cernan called. “I’m ready to give you an E-Memory dump.”

“Okay, we’re ready to take it. Go ahead.”

With the GUIDO console, manned by Presley and Ferguson, now receiving readouts of the erasable memory of the PINGS computer, I began to checkout our VHF near-distance communications. Both A and B VHF systems seemed to be operating correctly on Challenger’s side; however, when I checked to see if Evans could hear us on VHF, there were problems that took about ten minutes of back and forth “do you read?”, “I don’t read you”, “Loud and clear”, and “Switch to BRAVO (then ALFA)”. We finally got the two spacecraft, A and B VHF systems warmed up and working. Apparently, the system had to warm up more than had been modeled in the Lunar Module Simulator and the squelch level also was more sensitive than we had experienced during training. Communication systems have a mind of their own, believe me. These VHF checks actually should have been done earlier, before the S-BAND activation, but Evans had fallen behind the timeline with suiting up and the trouble finding stars he could sight on for his P52.

“Okay, Houston,” I reported. “I’m pretty sure the VHF is all right. …It [the voice quality] seems to have something to do with the SQUELCH setting and it’s probably because we’re so close [to each other].”

“Okay,” agreed Fullerton after getting approval from the LM TELEMU, “we concur. We’d like you to press on and not worry about the VHF anymore now.”

“Okay, Gordo,” Cernan responded. “We are [pressing on]. Here’re a couple of quick ones [for you to think about]. When I pushed the LGC DSKY (LM Guidance Computer Display and Keyboard) breaker IN, I did not get a RESTART LIGHT [on the DISKEY as expected]. The keyboard came up with 400 in R-2. The LGC [Caution] Light was already on, and it went off as prescribed. When I did a VERB 35 [to test the DISKEY LIGHTS], I got all the proper lights except, when the LGC and ISS (Inertial Sub-System) lights came on, the entire CAUTION AND WARNING dimmed. One more item: in our DAP setting, we are reading in our [Activation] Checklist [that] for R-1 [we should see] plus 645 and for R-2, plus 641. The DISKEY DAP [registers] came up plus 641 and plus 645. It just reversed those numbers. …And I am going to deploy the landing gear.”


“Cernan continued. “MASTER ARM is on, and [the system] B light is ON.”


“Roger. Are you ready for a landing gear?” Moving on without an answer from Fullerton, Cernan called to Evans, “Ron, if you read, the Landing Gear is coming [down] on my Mark (Fig. 8.7)…3, 2, 1 MARK. …Hey Houston. We got a good one [in view] out front!”

Fig. 8.7. The white arrows mark the landing gear deploy switch (lower) and its talkback window (upper). This is panel 8, located below the circuit breaker panel at the CDR’s left side. Note also the attachment clips for the cable restraints at bottom left. (Base photo NASA/ALSJ/Paul Fjeld).

“Sounds good. …We show them all deployed.” Fullerton was relaying that Thorson had telemetry from sensors showing proper deployment of all four Landing Gear, including the three we could not confirm, visually. On board, Cernan reported that our single Landing Gear talkback above the deploy switch showed GRAY, also indicated full deployment, as it would have shown BARBER POLE if just one had not fully deployed. Challenger moved closer to becoming a lunar landing craft.

“The PRIMARY EVAP[ORATOR] FLOW [start] time…108:16:55,” I reported, giving Fullerton the time recorded earlier. “And I’m ready to copy your [AGS] Abort constants and a DOI-2 PAD (Preliminary Advisory Data).”

“Okay, Jack. Here come the Abort constants: [DEDA entry] 224 is 6…”

“Stand by, Gordy,” I interrupted, as Cernan and Evans worked to close the CSM/LM tunnel.

After the VHF seemed okay, Evans had finished installing the PROBE and DROGUE in the CSM/LM tunnel and then said, “I’m getting the PROBE [electrical] umbilical installed now. …Okay, Gene. Can you look at the capture latches? I’ve got it preloaded here now.”

Cernan responded through the tunnel with, “Is the PROBE locked?”

“What do you mean [by] PROBE locked? …Yes, it was locked. …Oh, [you meant to say] DROGUE! …Yes, yes, it’s locked in there.”

“Capture latches look good.”

While Cernan waited on Evans, I went ahead with the AGS update. “Okay, Gordy. You can go ahead, and you have DATA on the UPDATA LINK [for the PINGS].”

Fig. 8.8. The position of the Data Entry and Display Assembly (DEDA) on panel 6 located in front of the LMP between the yellow hand-holds just to the right of the DSKY (Fig. 8.4↑ shows the LM-12 DSKY) in a photo of a LM mockup in storage at the Smithsonian Institute. The engine Start/Stop/Restart pushbutton is in the grey cover housing behind the left hand-hold. Note also 3 of the LMP’s white restraint cables at lower right (Mockup donated by Grumman Aerospace; National Air and Space Museum (cc0) photo NASM2019-07214).

“Okay. We’ll have the UPLINK in a minute. [DEDA (Data Entry and Display Assembly, Fig. 8.8) address] 224 is 60470, 29364, 60386, 00594, 32772, 54404. Go ahead [with the read-back].” This input data was for future reference when I activated the AGS. It would give the AGS computer knowledge of America’s predicted semi-major axis of the elliptical orbit to which the AGS would target an insertion burn during an Abort.

After I read the numbers back, Fullerton said, “That was a good read-back. Ready with DOI-2 when you are.”

“Okay, Gordy. Go ahead.” This (Preliminary Advisory Data) PAD information would be entered into the PINGS to perform the DOI-2 burn, using the RCS thrusters. DOI-2 would take place behind the Moon at Challenger’s apolune (maximum altitude) about one hour before Powered Descent Initiation (PDI). For Challenger, the burn would give a slight reduction in orbital velocity and lower our altitude 3-4 nm at PDI and thus save us fuel for landing.

“Okay, …its DOI-2: TIG (ignition) time is 112:02:40.92. NOUN 81 (CSM delta-v required in the P30 external burn program) is a minus 0007.5 [fps]; [DELTA-Vx and] DELTA-Vy [are] plus all balls (zeros); and DELTA-Vz is plus all balls; …NOUN 42 [is] 0061.5 [nm]; [pre-PDI apolune], plus 0006.7 [nm]; [pre-PDI perilune], and 0007.5 [fps] [delta-v required]; burn time [is] 0:22 [sec], 000, 074; …And [AGS] 373 (ignition time) is a 0122.7. …The AGS DELTA-Vs are NA (not applicable).” For its internal clock, the AGS used the difference between a specific event and the Ground Elapsed Time when the AGS was initialized. In this example, DOI-2 ignition would occur 122.7 minutes after I activate the AGS, which would happen about 20 minutes after we undock from America, or about two and a half hours from this point in the Challenger Activation Checklist. The DOI-2 burn, therefore, would occur in about four and a half hours. We had a lot of Checklist to go through before then.

I then told Fullerton, “I’m going to start the [ASCENT]/LUNAR BAT[TERY] CHECK, and it’ll be silent.”

“Okay. We’re watching,” which meant that Thorson would follow each of my Checklist actions by monitoring the telemetry’s response. Meanwhile, Cernan called Evans, “Ron, how soon are you going to be able to give me the [IMU] coarse align?”

“I can do that now; [I can] put the tunnel hatch in a little bit later.”

“Give me MIN DEADBAND, ATT[ITUDE] HOLD. I’ll [also] need your NOUN 20s, when you get a chance.”

“Okay, Gene,” Evans responded. “You’ve got MIN DEADBAND, ATT[ITUDE] HOLD, now.” This tight control of the motion of the two spacecraft was required for this transfer of America’s gyro platform alignment.

“Stand by. …I need your numbers then…NOUN 20.” Cernan needed the current yaw, pitch and roll angles of America’s PINGS Inertial Data Coupling Unit (ICDU) to start the coarse alignment of Challenger’s Inertial Measuring Unit (IMU).

Cernan repeated, “Ron, I need your NOUN 20 numbers.”

“There we go,” Evans finally answered. “Plus 356.95, plus 106.34, and a plus 001.49.”

Cernan read back the angles, but then Fullerton interrupted the procedure with, “Challenger, we want to get the attitude tweaked back to closer to nominal before doing the coarse align.”

Wants to what?” Cernan asked me.

Wants to tweak the attitude up closer to normal,” I told him, having been listening while checking on the batteries.

“Hey, Ron, they want a more normal attitude for you. You’re not quite nominal.”

Mattingly then separately told Evans, “In order to get a better drift check, they’d like to tweak up the attitudes before they do that coarse align. So how about doing a VERB 49 tweak back to the original undocking attitude.” GUIDO’s Presley always had precision in mind. VERB 49 let Evans enter the nominal attitude of 0, 105, and 0 and command the computer to use his RCS make the small change to be back at that attitude.

“Okay, that’s the what: 0, 105, and 0?”

“Yes, sir.”

“Stand by Gene. We’ll get back here.”


“Okay, Houston, America. 0, 105 and 0, correct?”

“Yes, sir.”

“That’s interesting. I don’t know how it got off attitude,” Evans mused.

“Yes, I was going to ask you the same thing. You might have knocked a [control] stick or something while everybody was flailing around down there [in the LEB]…”

“Maybe I hit the stick or something. Yes,” Evans agreed.

“…And, Ron,” Cernan inserted, “let me know when you’re tweaked up and then go to MIN DEADBAND, ATT[ITUDE] HOLD.”

After a brief delay while Evans maneuvered back to the desired attitude, he said, “Okay, Gene. We’re MIN DEADBAND, ATT[ITUDE] HOLD at 0, 105 and 0.”

“Okay, read out NOUN 20.”

“VERB 6 (decimal display), NOUN 20,” Evans said to himself and then read off, “000.32, 104.40, 359.55. Okay?”

“I got all those,” Cernan replied. During these interchanges, Fullerton told us that the computer had GUIDO’S new telemetry uplink, and we took back control of our PINGS.

Then it was my turn with the batteries. “Okay, Houston, I skipped a step on LUNAR BAT – OFF/RESET. I’ll go back.” This actually was a step that Cernan needed to do on his side of the cabin, and I missed interrupting his work with Evans.

“Jack, …we think you missed a step…,” Fullerton came on a second or two later. “…LUNAR BAT – OFF/RESET.” At least I caught the mistake before my good friend Dick Thorson could tell Fullerton about it.

“Yes. That’s right…that’s affirm. I’ll go back. Stand by. …Okay. I’m back to LUNAR BAT – OFF/RESET.”

As this interchange took place, Evans was trying to finish up closing out the tunnel as well as check out the capture latches that had not worked properly during extraction of Challenger from the S-IVB. “Okay, Houston. I forgot to release the docking latches. Okay? I’ll go up and release docking latches 1 and 7.”

“Okay,” Mattingly agreed.

“Well, if I just put the… I was going to say you could read the PROBE temp if I put the [DOCKING PROBE] circuit breakers in.”

“There’s [latch] number 1. One release, two releases, and it’s (the latch) free. [Latch] Seven. One release, two releases, and it’s free.”

“DOCKING PROBE circuit breakers, two of them, are going CLOSED. MAIN A, MAIN B, PROBE EXTEND/RELEASE is going to RETRACT…Ah-ha! I got two barber poles.” The barber poles displayed for the two sets of capture latches indicated that one latch in each set remained released.

“That’s a good sign [that things are working properly],” Duke added.

“Docking PROBE circuit breakers going OPEN. …Okay. EXTEND/RELEASEs [to ON]…and they (talkbacks) went GRAY, of course, when they went OPEN (all 12 were now OPEN). …Okay. EXTEND/RELEASEs to OFF. Verify PROBE extend latch engaged. …Well, I’ll go back. It wasn’t [engaged] awhile ago, but I’ll go look again. Only if we hit EXTEND with the circuit breakers – IN. …Oh! Mighty fine. It’s (the latch) still back inside there. Extend latch is still engaged.” This completed verification that all would be well with the PROBE and capture latches when we returned from Taurus-Littrow, although made somewhat confusing with Evans’ running conversation with himself.

While this went on, Cernan continued with the coarse alignment of Challenger’s guidance platform. “Okay, Gordy. For the LM, I’ve got 300.88, 284[00], and three balls [point] 45 [degrees]. How does that sound?” The second angle of 284 rather than the 104 for America related to the fact that Challenger’s pitch orientation was 180 degrees different than America’s.

“Stand by. We’re checking. …Okay, Geno. [GUIDO says] Those angles are okay.”

“Figured they were. They’re going in.” To do this, Cernan used a VERB 41 entry to load the COARSE ALIGN IMU angles into the DISKEY. This caused the FDAIs (Flight Director Attitude Indicators or “eight balls”) to move and show that our yaw was 000, pitch 284, and roll 060 relative to America’s orientation. He then entered the LM’s coarse alignment angles into our NOUN 20, followed by a VERB 40 NOUN 40 to zero the Coupling Data Unit (CDU). This in turn caused the “NO ATT[ITUDE]” caution light to go out as the PINGS now knew the spacecraft was in an attitude that matched the IMU alignment.

Next, Cernan set up the E-Memory Operator (erasable memory) in the computer and put the computer in its idle Program (P00) for the time being.

“Okay, Ron,” Cernan called a minute or so later, “on my mark, I’d like a [VERB] 06 [NOUN] 20.” This simultaneous call up of America’s and Challenger’s alignment angles put them on the downlink to Mission Control and would give GUIDO a measure of how well the coarse alignment went. The differences between the two alignments, however, were less than a degree in all three axes. This meant that our up-coming P52 fine alignment with two star sightings should start with the planned navigation stars in the telescope’s field of view.

“Standing by. Go ahead,” Evans replied.

“Okay. 3, 2, 1, MARK it!”

“[America’s angles are] 000.44, 104.63, 359.69,” reported Evans.

“Got those.”

“Okay, Challenger,” called Fullerton, “we’ve got those angles here on the ground…for both spacecraft.”

“Fine, Gordy.”

Half a minute later, I called with, “Okay, Houston, ED (Explosive Devices) BATs [are] 37.2 [and] 37.2 at 109:14:00. …And all battery indications on-board were normal, once I got started [on the right switch sequence].”

“They look good to us, also.” This completed a nearly 10 minute process of systematically checking each of our batteries, first the two Ascent batteries and then the four Descent batteries, for adequate currents and proper talkback indications (BARBER POLE or GRAY) at various ON-OFF positions. Taking the Ascent Batteries off-line at the end constituted the final step before checking the ED BATs. The Ascent Batteries would be put back on line before Powered Descent so that they would be ready if we had to Abort off the Descent Stage.

“Ron,” Cernan requested, “I want you to stay in that MIN DEADBAND – ATT HOLD [configuration]. I’m going to do a P52.”

[Star sightings for the P52 in the Lunar Module used the one power (1 ×) Alignment Optical Telescope (AOT, Figs. 8.3­a,b↑, and Fig. 8.11↓), mounted near the top-front of the cabin, above the DISKEY, and physically anchored and aligned to the structure containing the Inertial Measuring Unit (IMU) gyroscopes. The MIT Instrumentation Laboratory created the AOT as an integral component of the Lunar Module’s PINGS.[26] The AOT optics has a reticle pattern consisting of crosshairs (cursor) and an Archimedes spiral. “MARKs” on a star would be made as the star moved across each of the two cursor lines and across two places on the spiral. A bad mark could be rejected using a button on the AOT. For reference, when a MARK is taken, the computer records the time of each mark and the angles of each IMU gimble (gyroscope rotation axis). The plane that included the star is defined by the angle between any two marks and is recorded on a counter. That angle then is entered into the P52 computer program and could be used to realign the IMU gimbals. Each alignment required observations on two stars. Any number of marked pairs could be recorded and the PINGS would average them.

Cernan closed the AOT LAMP circuit breaker (see ahead to Fig. 8.32­­↓) that activated ten small red lamps positioned around the edge of the optics. These lamps made any lens imperfections show up as red while stars would be white points. Heaters in the AOT prevented fogging in the optical train. Cernan then entered VERB 37 to load P52 and enter the alignment program. As we were at the attitude anticipated by the Flight Plan, the DISKEY asked for the Star Code for Dubhe, star number 300, to be entered with a PROCEED on the keyboard. Then, Cernan told the computer that he would mark with the Cursor, first, and, after another PROCEED, we could begin to MARK and record the angles displayed by the AOT counter. The MIN DEADBAND, ATT HOLD provided by America, still would allow enough drift across the star field to allow the required marks.]

While Cernan set up for the fine alignment, I brought Mission Control up to date on a few items I had noted as I brought systems on line when out of communications.

“Houston, this is the LMP. …A couple of minor things on the backside checkout. The secondary glycol pump, when I started it, the sound and the pressure [gage reading] were ragged. …[It] oscillated around 20 psi and then stabilized. After about 15 seconds, it (the pump) sounded smooth. It had a sound as if it was cavitating a little bit; but, after that, it was smooth. Over.”

“Copy that, Jack.”

“And on step 3 on page 3-15, …when I went to SUIT FAN 1, I got a MASTER ALARM, …but all other indications were okay, and the MASTER ALARM [light] reset [when I pushed it].” Having reported this, I looked at the Checklist again and said, “Okay. I’m sorry. I misinterpreted the words there; I should have gotten that [MASTER ALARM]. Forget that one.” (The Master Alarm light is the largish, square, grayish button on panel 2 just to the right of the eight ball in Fig. 8.3b↑. A similar Master Alarm button is on CDR’s panel to the left of his eight ball.)

“Roger. We (Thorson at LM CONTROL) concur.”

“Okay, Geno. You need some help [with that P52]?” In case I was required to do an alignment, I had practiced P52s using the AOT during many solo runs in the Lunar Module Simulator. For the next fifteen minutes, Cernan marked on the two stars called for in the Checklist while I loaded the computer with the angle data he read off the AOT counter.

Turn some of the lights down. …Okay, Jack, that’s what the [star] number ought to be. Dubhe’s the first star. And those are what the Spiral/Cursor numbers ought to be, so let me go to the Cursor first – [should be] 170 [degrees and] something.” Cernan had been practicing some Marks.

…What star you got, [number] 300? Or no, what star?”

Dubhe. Dubhe. Yes, she’s going to be right in there.”

Okay, and those are the numbers,” I verified from the DISKEY… “Okay, that’s good. Okay. You ready to Mark? What do you want first?

Cursor. …Can you hold that [foot] down? I need it to hold. …I can’t stay up [here at the AOT]…” In his suit, Cernan could not easily stabilize himself with his head near the AOT.

Couple it [around the DISKEY].”

Wait. I’ll put my foot back here [around the Ascent Engine cover]. Okay, you ready [to Mark]?

Go ahead. Which one…Cursor?” I wanted to be sure.

Yes, yes…GO.” Dubhe drifted across the AOT reticle.


17108,” I repeated as I loaded the numbers. The angles actually were in hundredths of degrees – 171 point 08.

Hey, we’ve got to turn these overhead lights out, Jack, if we can. …The floods. …right up here.”

Well, let’s see,” I said, reaching over to Panel 3 on Cernan’s side of the cabin. “[There,] they are down.”

Ready to Mark?”

Wait a minute. …Go ahead”

Fullerton, not thinking about what we were doing, interrupted with, “Jack, we’d like to take a look at the glycol pump pressure. Can you close the GLYCOL PUMP SECONDARY pressure [circuit] breaker?”

“Let us finish this [P52]. …Go ahead, [Gene]

Oh, I’ve lost it now. Stand by. …MARK it. 17108. Yes that’s good…”


Yes. …What’s he want?” referring to Fullerton’s call.

I’ll get it. [He wants] SECONDARY.”

What? The SECONDARY?” Cernan had missed what Fullerton had said about the glycol pump.

“Gordy, you want the SECONDARY [PUMP circuit breaker]?”

“That’s affirmative – Panel 16, GLYCOL PUMP SECONDARY breaker – third row, in the middle (Fig. 8.6↑, white arrow).”

“Okay,” I replied and pushed in the breaker. “We’ve got a GLYCOL light, and the temperature is 50 [degrees].” To Cernan, I said, “I think that’s in the Secondary Loop.

“Okay,” Fullerton said as he looked at Thorson. “The pressure looked good there. We’d like that breaker back open. The MASTER ALARM you have is normal.”

“Roger. Understand it.”

Stand by. Spiral…31377.”


There’s a lot of light coming in [the AOT from] somewhere. It’s probably Earthlight.”

31303,” Cernan said as he took another pair of Marks on the Spiral.

31303,” I repeated as I loaded the angle in the DISKEY.

Now, how many more do I need?”

You need two more [angles on the Spiral].”


Okay, 31245.”


Okay, that’s it. …Now, the next star. Okay, we’ll PROCEED. …Okay, you like those numbers [from the first star]?” I asked Cernan before hitting PRO.


Yes. Okay. All right, VERB 21-ENTER…” I was talking to myself, preparing to tell the PINGS to move the AOT to another detent position so that the new star would be visible. [Now] you want a 111, [that’s] Aldebaran. ENTERED. PROCEED.”

Why don’t you write those [angle differences] down?” Cernan said before I went to the new star entries.

Yes, I will.”

And I’ll do, obviously, Cursor first.”

Okay,” I said after recording the angle differences for the Dubhe sightings, “111 [is ENTERed]. You ready to Mark…Cursor?”

Yes. …Get the lights if you can.”

All of a sudden, we heard from Evans. “Son-of-a-buck – I hit the [control] stick again. Now I have to unlock it [to maneuver back to attitude.”

“Ron,” Cernan called hurriedly, “keep in MIN DEADBAND – ATT HOLD. I’ve got to finish the P52.”

“Okay. You want me to maneuver back to attitude, Gene?”

“No, just stay where you are.” The Challenger’s guidance system, although only coarse aligned at this point, would take into account Evans inadvertent change in attitude.

“We’re out of attitude just a little bit.”

“No, just stay where you are. …Just stay where you are, and put it in MIN DEADBAND.”

“Well, I’m in MIN DEADBAND, but I maneuvered out of attitude. You want to go back to regular attitude?”

“No! N-O! No.”

With that taken care of, I said, “Alderbaran is your star. …Oh! Do you read me [Gene]?…I don’t read me very well.”


329…61, 32961. …Go ahead.”


Say that again. I…Ron [drowned you out],” I requested.

I wish he’d go off VOX (voice activation)…32947.”

Let me turn this VHF [off]. …Okay,” I said, 32947… Hey, Ron. This is Challenger. We’re going to be off your loop for a while, so we can finish the [star] mark.”

Then Cernan changed his mind about the last Mark. “I don’t like that. I don’t like that. I want to reject it.”

Okay. …ENTERed, PRO. You can reject it [with the Reject Push button on the AOT].”


33100. …Go ahead. One more on the Cursor.”

32972. Son of a gun!”

What’s the problem?”

It’s just hard to…focus everything in there.

32972. …Okay, and you’re clear on Spiral.”

Okay, …Ready to Mark?”

Go ahead. …Should be around 37.”


Whoops!” I miskeyed a sign.

That’s all right.”

Plus 04116. …Go ahead.”



Two more.”



Boy, I can sure see him maneuvering [across the star field].”

One more.”

Best I can do – 04407. Whew!”

Is he moving?”

Just like he did in the simulator the other day.”

Well,” I said, “they’re (the angles) not bad.”

Well, I’ll tell you. That’s an eye buster. You’re lucky. …Hello, Houston. That looked to be a pretty good alignment from where I saw it. There’s 07 for you.” Cernan meant the ‘06’ 93 display in P52 that gave the torquing angles for the fine alignment.

“Okay, We copy…

Here, I’ll copy those in here [the Checklist].”

“Okay, Challenger. Torque them,” said Fullerton, after a thumb’s up from Presley or Ferguson at the GUIDO console. With a PROCEED keyed on the DISKEY, Challenger had a functional guidance system.

[The time was] 109:34:5. …Make that 7.”

Jack, you go to centerline and zero up there [on the AOT].” This would put the AOT in its stowage position.

Okay.” As I stowed the AOT, Cernan put the PINGS computer in P00 (idle).

And I’ll pull the [AOT LAMP] breaker.” (Fig. 8.32­­↓, the 2nd switch to the right of the ORDEAL breaker marked by the arrow is the AOT LAMP breaker).

“Hello, America, Challenger,” Cernan radioed to Evans. “We no longer need your MIN DEADBAND.”

Challenger, America here,” Evans answered. “I’ll go back to CMC (Command Module Computer) [control].”

“Okay. But I would like a NOUN 20 from you on my mark.”

“Stand by. …Okay, Go.”

“…3, 2, 1, Mark.” The Ground Elapsed Time was 109:35:00.

“…002.15, 104.36, 359.69,” Evans reported.


You got those [angles copied]?” I asked Cernan.

Not yet. Ground will have them.” I would have liked to have these data recorded in our Checklist. I always worried about a loss of communications at a time when we might need to do a rapid re-alignment by ourselves.

We’re ready for RCS [pressurization], and we’re about 10 minutes behind,” I said.

Challenger, we’ve got the NOUN 20s, both spacecraft.”

Attitude Control

You picking up that first part [of the RCS Checklist]?” Cernan asked.


[After a great deal of discussion and analysis, Grumman engineers finally settled on a Reaction Control System (RCS) configuration that solved many problems related to attitude control, small velocity changes, thruster failures, and thruster plume impingement on the spacecraft skin.[27] They located clusters or “quads” of four small rocket jets at 45 degrees to the “z” or forward and back (roll) axis and the “y” or left and right (pitch) axis and in the plane of those two axes. Each jet produced 100 pounds of thrust. (Note that each F-1 rocket engine of the Saturn V first stage produced 1.5 million pounds of thrust, illustrating the immense span of propulsion technology required for Apollo missions.)

In each quad, one RCS jet thrust parallel to the “z” forward and back axis and one thrust parallel to the “y” left and right axis. Also, in each quad, one jet thrust parallel to the plus “x” or up (yaw) axis and one thrust parallel to the minus “x” down (yaw) axis with both directions parallel to the centerline thrust of the Descent and Ascent rocket engines. As the result of this configuration we would have two jets with thrust along each plus and minus direction of the spacecraft roll and pitch axes and four jets with thrust along both the plus and minus yaw axis. The 45-degree offset of the thrusters from the actual Lunar Module control axes, however, required the firing logic of the various control systems to compensate for each thruster’s off-center torque around the vehicle’s center of gravity. Those control systems included the Primary Guidance and Navigation System (PNGS or PINGS), Abort Guidance System (AGS), Digital Auto-Pilot (DAP), and Commander and Lunar Module Pilot hand controller inputs.

In addition, the four RCS quads also incorporated two fully redundant (identical but separate) systems of eight jets within the total of sixteen jets. If one system failed, the other could provide attitude control. Each RCS system, referred to as A or B, had its own tanks, pressure bladders, regulators, lines, and valves for fuel (Aerozine 50, a 50/50 mix of hydrazine and unsymmetrical dimethlhydrazine), oxidizer (nitrogen tetroxide), and pressurizing gas (helium). The fuel and oxidizer are hypergolic chemicals; that is, they ignite on contact, eliminating the need for an ignition source such as a spark. The Descent and Ascent Engines used the same fuel and oxidizer, and a cross-feed existed between the RCS and Ascent Engine fuel and oxidizer tanks in case the need arose to share propellants during an Abort or abnormal Ascent from the lunar surface. All in all, we were given a very ingenious approach to attitude control without compromising crew visibility and one that included the capability to thrust along or rotate about each spacecraft axis. The Marquardt Corporation became the RCS subcontractor to Grumman in early 1963.

The initial RCS items in the Checklist constituted the following: Recycle the SYSTEMS A&B ASCENT FEED (two) to CLOSED, then to OPEN, and then check that SYSTEMS A&B ASCENT FUEL and ASCENT OXIDIZER Talkbacks remain with a BARBER POLE indication, verifying that the systems are not pressurized; recycle the CROSSFEED switch between ASCENT tanks and RCS tanks to OPEN and then CLOSED; recycle the MAIN SOV (Shutoff Valve) switch for SYSTEMS A&B to CLOSED and then OPEN; and use the HEATER CONTROL knob for TEMPERATURE MONITOR and check the RCS QUADS at greater than or equal to 120ºF. All this switch cycling insured that no valve positions had changed during the heavy launch vibration and staging shocks while on the Saturn V. (All of the switches mentioned here, except Heater Controls (on panel 3), are to the left of the eight ball of panel 2— see Fig. 8.9 below for these switch positons.)]

[RCS quad] temperatures are good.” I said to Cernan


Then, I used the TEMP/PRESS MONITOR knob to check allowed ranges of pressures and temperatures for RCS Helium (2820-2380 psi minimum), propellant (40-100º/10-50 psi), fuel manifold (25-90 psi), and oxidizer manifold (25-90 psi) and that the RCS propellant quantities for SYSTEMS A&B were at 100%.

Fig. 8.9. Top Left & Right – (yellow arrows): Caution and Warning lights; Top Right – (pink arrow): ECS pressure gage. Top Left – (light blue double arrow): Mission timer at left in hr, min, sec; Event timer to the right in min, sec. Bank of 12 switches left of the panel 2 eight ball: Top row – (orange arrows): Systems A (left) & B (right) ascent fuel (left) and oxidizer (right) switches with talkbacks above each, up position ‘open’; down position, ‘closed’. Lower 2 rows – (white arrows): Systems A (left) & B (right) RCS quad switches with talkbacks above each, quads 1,2,3,4 counterclockwise from top left, each row – up, ‘enable’; down, ‘disable’. Crossfeed switch (blue arrow): up ‘open’; down ‘closed’. Main SOV (green arrows): Systems A (left) & B (right) switches with talkbacks above each; up ‘open’; down ‘closed’. Heater control temperature gage (upper red arrow): temperature monitor rotary switch; (lower red arrow): four detents to right of vertical measure RCS quads 1,2,3,4. Finally, the Temp/Press Monitor rotary knob is marked by the purple arrow on the lower left of panel 2. The four detents measure (left-to-right) the ranges for He, propellant, fuel and O2 manifolds. (Base photo NASA/ALSJ/Paul Fjeld).

[Initial] Helium is 3050 [psi],” I told Cernan. Helium would be used for pressurization of the propellant tanks.

Challenger, Houston, we’re ready anytime for the RCS pressurization. You might turn the [RCS] HEATER switch off.”

“I just got that [switch] and we’re going [to RCS pressurization],” I assured Thorson through Fullerton.


Then we ran through the pre-pressurization temperatures and pressures one more time with Cernan going down the list and me responding.


[Temperature] 70 degrees…[pressure] 25[psi], about.”

Let’s Go. Fuel?” Cernan acted impatient, probably because his P52 alignment put us behind in the Flight Plan.

…[pressure] 50.”


And [pressure] 50…no make that 60 on the oxidizer.”

Your quantity?”

The quantities are 100[%].”

On [circuit breaker Panel] 16 – LOGIC POWER [B], OPEN.”

B’s coming OPEN,” I replied. Using only the Logic System A to fire the explosive devices that would open the RCS to pressurization also allowed a check on System A to be sure it was fully functional. This is a good illustration of always being sure we knew the status of all redundant and backup systems.

Okay. …MASTER ARM is ON,” Cernan reported after throwing the switch on the panel below his left arm. “I’ve got one good light [on ED] System A.”


Why don’t you read them [the RCS Cue Card] to me,” Cernan suggested, as he had to look away from the Checklist and down to his left to see the EXPLOSIVE DEVICES switch grouping that would now be configured.

Fig. 8.10. The group of EXPLOSIVE DEVICES switches located just right of the landing gear deploy switch (see Fig. 8.7↑) below the circuit breaker panel at the CDR’s lower left (i.e., center part of panel 8 in Fig. 8.3a↑). (NASA/ALSJ/Paul Fjeld).


Well, [you mean] HELIUM PRESS RCS,” Cernan added after I had assumed he knew that was what we were working on. Should not “assume” anything in this business.

RCS – FIRE. …I’m sorry.”

Okay. HELIUM PRESS…I just don’t want to get the wrong one.” Cernan referred here to two switches just to the right of the RCS – FIRE switch that prematurely could pressurize the DESCENT or ASCENT fuel and oxidizer tanks.

Yes. Okay [to FIRE]?”

“Okay, on my mark. 3, 2, 1, MARK it. We heard it [the Explosive Devices detonation]!” The sharp crack of four simultaneous small explosions releasing propellants into the RCS feeder pipes caught both us by surprise.

Sounds like they filled up,” I observed. “175…I mean…180[psi]. Looks good.”

[RCS] REG [CAUTION] lights are off? Cernan noted.


And MASTER ARM is OFF. …Recycle all your [RCS FEED switches]…

Okay.” I then repeated the earlier switch cycles. CLOSED, CLOSED, OPEN, OPEN, CLOSED, CLOSED, OPEN, OPEN. They’re all okay.” This recycling was something Cernan and I decided to do because of the small chance that the ED detonations had shocked the valves enough to change their positions.

And your LOGIC POWER B [circuit breaker is] CLOSED?”

B is CLOSED,” I reported. Both LOGIC SYSTEMS were now on line for any emergency use.

And read the [tank] temp/pressures to me.”


“Okay, Challenger,” Fullerton called. “We (LM CONTROL) saw it, and it looks good. RCS looks good.”

Oxidizer and fuel [tanks] are both 180[psi].”


Propellant’s 180 [to the thrusters].”

That’s GO.”

And Helium is slightly under 3000.”

That’s GO.”

[RCS] Checkout. You ready?” I asked, moving to page 3-25 in the Activation Checklist. Every system’s checkout would determine if we were going to land on the Moon or spend our mission in lunar orbit, or just go home; but certainly the checkout of our attitude control capability was as critical as any.

Let’s go. You read it to me and we’ll press.” All the switches for this checkout lay directly in front of Cernan. (Fig. 8.3b↑­­, panel 1, lower left).









Switch Guards at 6 o’clock.”

Six.” This made sure we could get through the switch guards quickly to the MODE CONTROL switches if we needed to.

NO DAP light, off [verify].”

NO DAP light is off.” “No DAP” caution light meant we had a functional Digital Auto Pilot.

ACA/4 JET, Commander [hand controller], DISABLE.”

What do you want?” Cernan asked, possibly briefly puzzled that we would disable his right hand controller. This was so that we could test command signals to the RCS without firing the thrusters. “Okay.”

TTCA, both, to JETS.”

Okay.” We would initially checkout the left hand controller, that is, Cernan’s Throttle and Thrust Control Assembly, and then mine. (Fig. 8.4↑ shows Cernan’s gray hand Attitude Control Assembly (ACA); the TTCA cannot be seen in that image. Both controllers at my position are visible in Fig. 8.8↑ to the left and right of the yellow hand-holds).

Mine’s JETS,” I confirmed.

Mine’s JETS,” Cernan also confirmed.

Verify high bit rate with MSFN and [that] CSM [is] in WIDE DEADBAND, ATTITUDE HOLD.” MSFN stood for the entire Manned Space Flight Network, which had to be fully up for high bit rate telemetry to be transmitted or received.

“Houston, verify [you are getting] high bit rate,” Cernan radioed. “And, Ron, we need you in WIDE DEADBAND, ATTITUDE HOLD.”

Why don’t you put that [Checklist] here, if you can read it here? So we can [both see it].” The next part of the checkout required working with the PINGS so I held the book in place with my right hand just above the DISKEY so I could see its registers, clearly.

“Okay,” Evans replied. “WIDE DEADBAND, ATT HOLD. That’s what I’m on.”

Okay,” Cernan acknowledged and then pointing to the flood-lights, said to me, “Why don’t you turn these up?” We had left sunlight and entered darkness above the Moon.

Challenger, we verify High Bit Rate,” Fullerton reported a few seconds later.

Go [on with the checklist],” Cernan said to me.

Okay, QUAD flags.” As we would begin the checkout with cold fire checks, that is, check the command signals with no jets actually firing, the Checklist noted that, during the test, we would get red talkbacks over the eight QUAD ENABLE switches placed in front of us between the two eight balls and now in the OFF positions (Fig. 8.3b↑­­). “Okay. VERB 76 – ENTER.” This entry set the Digital Auto Pilot in a minimum impulse mode and gave us a NO DAP caution light as an alert that the DAP was not at full capability.

Go,” Cernan said after the entry.

NO DAP light on,” I verified. “VERB 11 NOUN 10 ENTERed, 05 ENTER.” These entries, with the computer in idle, or P00, would allow monitoring the telemetry readouts on the DISKEY. CDR [T]TCA [first]”.

“Okay,” Cernan called. “Here we go, Houston, with the Cold Fire check [of the RCS].” Again, there would be no actual firing of the RCS Thrusters because we had put the ACA/4JET switch in the DISABLE position.

Okay, you want to go up [first on your TTCA],” I noted.


“All set,” Fullerton relayed from Thorson and Legler.

And that’s good,” I said as Cernan moved the TTCA up and the 05 telemetry register on the DISKEY read 00252 which matched the correct readout listed in the Checklist.

252, read Cernan. “Okay?”

Okay, [now] down…125 is good…and [we have] the rest of the [red QUAD] flags.” The red flags under the QUAD switches reflected the fact that firings had been commanded but had not occurred.


[Now,] I’m going to do it [with my TTCA],” I said. “Up, 252; down, 125. That’s good.’

And non-return to zero [on the DISKEY], Cernan noted.

Okay,” I said, preparing for the right-left-forward-aft test of Cernan’s TTCA. “ENTER, 06 ENTER [to clear the DISKEY]. Okay…right – 220. That’s good. …[On return to detent] there’s [the] zeros. …Left – 140. Good. …There’s zeros. …Forward – 11 is good. …There’s zeros. …Back – 6 is good. …And there’s zeros.”

“Houston,” I called. “[Ready for] PINGS RATE COMMAND, Cold Fire; AGS PULSE, Cold Fire, Check.” This would be done with Cernan’s right hand controller, that is, his Attitude Control Assembly (ACA).

“All set,” Fullerton replied.


Evans interjected with, “Could you go to RECEIVE ONLY on the VHF for a little bit.”

Sure, Ron,” I said, laughing, since his communications with Houston also had been a nuisance, earlier.



VERB 77…”

Cernan, distracted by some outside sounds, said, “What’s all that stirring around? Is that the S-BAND [Antenna]? Yes?”

It’s his (America’s) attitude [changes], I [think], or maybe our S-BAND [reacting to attitude changes].”

It’s the S-BAND,” Cernan declared.

VERB 77, you got [it]?” I asked, referring to the computer entry that would set RATE COMMAND/ATTITUDE HOLD mode in the DAP. …RATE COMMAND meant that the thrusters would fire as necessary to reach the commanded rate imparted by the position of an out-of-detent hand controller. “VERB 15 NOUN 01 – ENTER,” to clear the DISKEY for the next check. “Okay, and 42 ENTER,” in order to read the numbers on telemetry, again.


CDR ACA to soft stop, pause two seconds at null. Roll right. …Okay, 50. …That’s good. Roll left.  …That’s good. Pitch up.  …47.  …That’s good. Pitch down. …7. …Wait a minute. You got it [in pitch]? [777]31. …That’s good. [Now,] register-2. Go ahead and yaw right. …27 is good. Yaw left. …50 is good. Okay.” The Checklist gave the numbers to which I was comparing our DISKEY readouts.

Better tell them where we are [in the Checklist],” Cernan suggested.

“All right, Houston. [We’re at] Step 4, AGS Rate Command Cold Fire, 4 Jet Secondary Coil Hot Fire Check.”

“GO. We’re looking good so far,” acknowledged Fullerton.

Then I warned Evans, “We’re going to have some hot fires here, in a minute.”

“Okay,” Evans replied. “Wait a min…hold it…America, Challenger…the hot fire…you want FREE, Challenger.” I had caught Evans in the middle of copying down a number of PADs and weights to load into America’s DAP.

That’s affirm. Go to CMC MODE – FREE.”

Challenger, America. You want FREE for your hot fire”

Tell him,” I asked Cernan. “He’s not [always] reading me, apparently.”

That’s affirm. We want you FREE, Ron.”

“Okay. Going to FREE now.” This put Evans in to a free drift mode, but with large combined mass of the two spacecraft, little attitude change would be imparted by the RCS thruster firings even with the DAP in RATE COMMAND mode.


Back at the Checklist, I said, “GUIDANCE CONTROL – AGS.”


ATTITUDE CONTROL, three, to MODE CONTROL.” Cernan did this but did not repeat my call-out; however, I continued to watch carefully that he took the called for action.



CDR ACA – [for each test] deflect [the hand controller] slowly to hard over [then] pause two seconds at null [coming back],” I said to prepare Cernan for the test.


Roll right.”

Oh!,” Cernan exclaimed in reaction to the loud noise and oil can effect of the thrusters firing on the outside of Challenger’s thin cabin shell.

Okay. Pitch up. …Okay, pitch down. …Okay, yaw right. …Okay yaw left.”


Okaaay,” I repeated, laughing at the thruster noise.

“Houston, [AGS] hard-over looked good from here,” Cernan reported.

“Okay, looked good down here,” Fullerton replied.

“All right, Houston,” I continued. “PINGS MINIMUM IMPULSE Hot Fire Check.”

“Okay,” replied Fullerton. LM CONTROL was ready to watch.

GUIDANCE CONTROL – PINGS, VERB 76 – ENTER [to set the DAP in MINIMUM IMPULSE mode], NO DAP [caution light] ON. …Okay, we need to close our [RCS SYSTEM A & B circuit] breakers. …Okay my four are CLOSED.” (Fig. 8.6↑, top bank surrounded by yellow striped tape).

And my four are CLOSED,” Cernan reported. These eight circuit breakers provided electrical power to the RCS QUADS for operation under PINGS control. On the earlier AGS hot fire check, power had been routed through the AGS circuit breaker. For redundancy, the eight breakers were divided four apiece between the A and B power buses. If one power bus failed, control could be maintained with the eight remaining thrusters, appropriately distributed two to each thruster quad.


Uh-oh,” Cernan said, looking at one of the RCS QUAD talkbacks that had remained red during this recycling of the instrumentation system.

Try [tapping],” I suggested, one of my solutions to many things.

There they go!,” we both exclaimed as the red turned to gray.

“Okay, Houston. We have a sticky talkback, red, on SYSTEM A, QUAD 4. And it went gray with a tap.”

“Okay, Jack.

Where are you?” Cernan asked.

Pointing to the middle of page 3-27, I continued, “VERB 11 NOUN 10 – [ENTER], 31 ENTER. Register-1 is 67777. CDR ACA, out of detent, [move] 2 and a half degrees, pause two seconds at null.”

The pulse?”

Okay, 57 is good. Roll left…37 is good. Yaw right twice…slowly.”

Tell me to do it again.” Never pays to rush, even though we had done this check many times in LMS-2. (Lunar Module Simulator-2 at the Kennedy Space Center was our primary simulator for the last six months before launch, with LMS-1 located back at the Manned Spacecraft Center. LMS-2 always received the latest updates, for obvious reasons.)

Okay,” I replied as Cernan moved the hand controller for a right roll. That’s 67. …Now do it again. …Okay, that’s good. …Now yaw left twice. …73. …That’s good. Okay, that’s [a] good [test].”

Two different thrusters are firing [alternately],” Cernan explained to himself as to why the yaw test was done twice in each direction.

Yes,” I agreed and pushed on. “VERB 48 – ENTER, VERB 21 – ENTER.” These entries would tell the DAP that we now would load data.


31022. PROCEED…and a VERB 34 – [ENTER to terminate the DAP data load routine], VERB 11 NOUN 10 – ENTER, 31 ENTER. …Okay. …CDR ACA, out of detent 2 and a half degrees, pause two seconds at null. …Pitch up. …76 is good. …Pitch down. …75 is good.” That did it for the hot fire checks, and I started to let Evans know.

He won’t hear you,” Cernan reminded me.

“Ron,” he called, “the hot fire checks are complete. You can go into WIDE DEADBAND, ATTITUDE HOLD.

“Okay, Challenger; America. We’re at ATT HOLD. You didn’t get very far off [attitude] that time [with the firings] either. That’s good.” This resulted from having the DAP in MINIMUM IMPULSE MODE rather than RATE COMMAND as in the AGS hot fire check.

“Yes, I think we got them all.”

Challenger, those [firings] all looked good here,” Fullerton said, relaying the “okay” from Thorson at the LM CONTROL console.

“Okay, Gordo. Understand.” We had put another activation milestone behind us.

Hatch Closing and Rendezvous Radar

In order to close the hatches between the two spacecraft, we needed to verify that the equipment had been properly configured that would be needed for docking on our return from Taurus-Littrow. This included seeing that both the electrical umbilicals we had used had been taken back and stowed in America. Challenger’s DROGUE Lock Levers had to be engaged and flush and the three Capture Latches on the PROBE had to be engaged and locked so that it would function properly when we came back. I inspected the upper hatches’ exterior insulation and made sure that insulation flaps around the handles were secure.

Well, you verified all this, didn’t you, Gene?”


Electrical umbilicals?”

I got…[no], he (Evans) confirmed that; I confirmed the Capture Latches.”


He called them out.”

Okay, I’ll [double] check that.”

You can check that stuff when you go and close the hatch,” Cernan continued.


“Okay,” Cernan called to Mission Control as he began the Rendezvous Radar tests. “We’re on the top of 3-28, Gordo.”

“Roger, we’re with you.”

[Challenger’s Rendezvous Radar system consisted of the necessary electronics and a dish antenna mounted at the top front of the spacecraft. The antenna transmitted a 9832.8 MHz. radar signal to a transponder on America with a 9792.0 MHz (+/- Doppler frequency shift) signal returned to the antenna. Along the line-of-site to America during the rendezvous sequence, the system would measure range (timing of the sent and returned signal), range rate-of-change (Doppler changes in signal frequency), beam angle (referenced to Challenger’s structural axes), and angle rate-of-change. Gyromotors in the antenna provided stability relative to motions of the Challenger that might affect angle rate-of-changes.[28]

The Gemini Program demonstrated use of radar to provide range and range-rate data directly to the crew of an active vehicle during orbital rendezvous. In 1965-66, when Grumman and NASA sought weight reductions in the Lunar Module, NASA set up a technical competition between the RCA radar system Grumman had proposed and a less pilot-friendly optical rendezvous system proposed by Hughes Aircraft. After these tests, both Grumman and NASA recommended using radar. The weight and cost savings attributed to the optical system proved to be less than originally thought and the Astronaut Office, based on the Gemini experience strongly supported using radar because of more rapid response relative to range and range-rate information.[29] ]

Umbilicals [from America]; looks like there’re off,” I observed as I floated up to the hatch area.

Challenger; America.”

“Go ahead, Ron,” Cernan said.

“I’m going to turn off [my Thruster] B-3 and also my roll jets, and then I’m going to undo the docking latches.” Evans is referring to his checklist reminder that a thruster on America could impinge on our un-stowed radar antenna at this close range and to roll jets that, if inadvertently fired, would impose rotational torque that could damage the PROBE’s three capture latches.

“Okay. You want to verify your [RENDEZVOUS RADAR] TRANSPONDER is OFF as well as B-3.”

“Yes, sir. Verify TRANSPONDER is OFF.”

“Okay, and you did get the [electrical] umbilicals, right?”, Cernan asked.

“Say again about ‘umbilicals’.”

“You did get the LM to CM umbilicals? Right?”

“All I get is ‘umbilicals’. I didn’t get the question.”

“Did you disconnect the LM to CM umbilicals? Verify.”

“Verify. I have those down here [in the LEB].”

“Okay, very good.”

“Jet Bravo 3 is OFF,” Evans then reported.

Meanwhile, I closed the hatch, saying, “Geno, it’s (the hatch handle) locked, to the yellow [limit mark], and it’s (shaft) full out [of its slot].”

And it won’t turn?”

And I felt it (the internal latch) pop. It won’t turn…and it’s tight.” Of course, the handle, if its shaft were pushed back into its slot against an internal spring, allowed for a rapid intentional release of the latch.

And overhead [CABIN DUMP VALVE is] AUTO and locked?”

I gave Cernan a thumbs up, as Fullerton started a long statement about our earlier concerns about the PINGS self-test.

Challenger, Houston. We cannot completely explain the startup indications you had on the PINGS, but there’s no great concern. You’re looking good so far. The DAP gimbal trims are no problem; don’t bother changing them. And there will be no PIPA (Pulsed Integrating Pendulous Accelerometer) bias update, yet anyway. Over.”

“Understand. Was the checklist written backwards on that?” Cernan asked.

“A Cape (Kennedy Space Center) problem on their [original loading] tape, and they had it reversed. But it’s in the noise level, anyway. No problem.”


After this review was over, I said, “We need to get our LEVA (Lunar Extravehicular Visor Assembly) bags.” These protective exterior coverings and visors, that protected the helmets and provide eyeshades, needed to be secured on the Ascent Engine cover. “Let me get down [from] here first, Geno.”

Working through the Checklist items for the RENDEZVOUS RADAR SELF TEST, Cernan had set circuit breakers and switches so that he could manually slew the radar antenna and monitor the movement of error needles on our eight balls. As he went through the prescribed antenna movements, all the error needles responded as required.

Challenger, Houston. You have a GO for UNDOCKING and SEP[ARATION].”

“Roger; understand. A GO for UNDOCKING and SEP.” This GO assumed that the checkout of the Rendezvous Radar would continue to go well, of course, but we were approaching a loss of communications again and undocking and sep would occur on the lunar far-side as planned.

Continuing with the Checklist items, I asked Cernan, “Can you give me your LEVA bag when you get a chance?”

Geez, Jack, I don’t know if I can,” he replied, annoyed. This request had caught Cernan in the middle of his tests of the Rendezvous Radar.

For several minutes, Evans had been working on releasing all of the Capture Latches prior to undocking and finally reported, “By golly, they’re all off. Hey, Challenger; America. You’re hanging on those two little bitty things.”

“Okay, fine, Ron.”

Challenger, Houston. You’re one minute to LOS and we’ll see you when you get around to the other side, independently.”

“Gordo, I understand. I’m in Step, 4, [page 28, and] RENDEZVOUS RADAR MODE is to AUTO. …The radar has come out [of its stowed position], and I’m in RADAR TEST now.” Step 4 activated the radar’s self-test and drove the Range Rate Tape, the X-pointers, and eight ball needles in specific ways that Cernan monitored, closely.

“Jack, just a friendly reminder to do the LOS procedures on the steerable [S-BAND antenna].”

Yes. …What do I…Where are those [procedures]? Okay. …Where’s my book? Lost my bag…supposed to take that one.” Clearly, I had lost track of the LOS procedures to which Fullerton referred. Finally, I found them in the Checklist and put the Antenna’s TRACK MODE in SLEW, placed it pointing AFT, and set pitch and yaw angles needed for re-acquisition at AOS in about 47 minutes.

Right after LOS, we got into this minute-long exchange with Evans who persisted in talking to himself with his voice activation (VOX) switch ON.

Hey, Challenger; America. I’m going to RECEIVE ONLY, B DATA. …Hey, Challenger; America…”

Okay, Ron,” a busy Cernan, replied. “Stand by, please!”

“Challenger; America.”

Hello, Ron,” I joined in. “How do you read?”

B is OFF, A is SIMPLEX,” again, talking to himself.

How do you read, Ron?” I asked again.

Evans continued to talk to himself and then said, “I don’t read you, but I’m going to put the hatch in.”

Hey, Ron, how do you read? How do you read, Ron.”

Okay, I got you that time, Jack.”

I think your VOX is cutting us out. When you talk to yourself, I think you cut us out,” I tried to explain, nicely.

You read me okay?” Evans asked.

Yes, you’re loud and clear, but turn off your VOX!”

Okay, I’m fanning too much, huh?”


Laughing, Evans continued to talk to himself, “I can’t read you right now. That doesn’t [help] too much.”

Turn off your VOX!” I was beginning to get frustrated.

Okay! Just a minute!”

Just like in the simulator,” I said to Cernan, referring to Evans talking to himself. “Just like in the simulator…” To Evans: “Yes, I think that’s pretty good.”

Okay, hatch is going in,” Evans concluded.

Excuse me, Gene…What can I do to help you [with the radar test].”

Aaah…could read some numbers. And see how…why don’t you set that [event timer] clock to undocking. …That would help.”


Hey, Challenger…”

That came from somewhere,” I joked as we were out of communications with Earth and, at first, it did not sound like Evans.

…America. You verify your hatch valve’s in AUTO?”

Ooooh. …That’s verified, Ron,” I answered.

Okay, I’m going to vent the tunnel.” He, of course, also had closed off his end of the tunnel and then checked the integrity of his pressure suit prior to undocking.

Still moving through the Rendezvous Radar tests, now involving its interface with the PINGS, Cernan said, “Man, it’s hot. We don’t have any LCG [cooling] water, do we?”

Sure. Should have.”

Sure like a squirt of it. Boy my eye’s watered so much, I can’t believe it.” Cernan may have irritated his eye during the P52 star sightings.

Okay.” I turned the LIQUID COOLED GARMENT valve to COLD and cooler water began to flow through our underwear.

Got to watch that one right there.”

Yes, I’m watching. You mean the cabin [pressure]?”

No, the [RCS QUAD] talkback.”

Oh, yes.”

Oh, that feels better. Oooh.” The cool water had reached Cernan.

Okay. [GET for undocking is about] 110:30. We didn’t get an undock time update, but… Hey, Ron,” I called, “what are you using for undocking time now?”

I’m looking…Wait a minute.

Cernan got enough cooling and asked me to “Pull that [cooling control] when you get a chance. That’s just what the doctor ordered.”

110:27,” Evans reported as the undocking time he had.

Copy, 110:27 [GET],” I replied. “Okay,” setting the Event Timer, “coming up on 27 minutes [to go].”

Radar is all looking good,” Cernan concluded… “When you get a chance,” pointing to the Medical Kit, “if there’re any eye drops in there, …I won’t be able to put them in here [with the suit on]. …Well, I might. …I’d like to put something in my right eye.”

What did you get…a particle in there or…”

No, I don’t know. It’s just been watering.”

I then moved over and put a drop in his eye, musing to myself, “Let’s see, I don’t know what I have to do here.  …We’ve got to do a Pressure Integrity Check.”

Just like the simulator, …only better,” Cernan said, referring to the Rendezvous Radar checkout.

Suit Loop and Cabin Pressure Integrity

“Okay,” I continued, “I’m going to get it set up for an [Pressure] Integrity Check, Gene.”

Hello, Ron…you can use [Thruster] B-3 if you need it.”

Okay, I’ll turn it back on here, then. Takes a lot longer to depress the tunnel – to vent the tunnel – than it does in the simulator.”

Yes,” I answered. “Okay, we don helmet and gloves here. Are you through [with the Radar tests]?”

Yes. …Okay, let’s do it. …Make sure the cap’s off your [PGA] relief valve.” PGA stands for Pressure Garment Assembly, that is, the space suit, and this relief valve would protect the suit against an over pressure.

Yes, mine is off.”

Evans called, again. “Are you through with your Rendezvous Transponder Test?”

Sure am, Ron.”

We’re a little bit behind,” I added and then joked, “Somehow, we got away [from you] with our helmet bags, …which is probably just as well (since helmet protection would be needed after work on the lunar surface).”

Be careful what you put on the Comm Panel,” Cernan cautioned, “because we’ve got a hot RCS now.” He may have been talking to himself about his audio panel under his left arm, next to the left hand controller, as nothing on the Communications Panel under my right arm could fire the RCS.


Yes, if there’s someplace where we can legitimately put these [bags]…”

I’ll find a storage spot for them,” I offered, “if you can hang on to them for a minute.”

Well, I could put them in one of these bags right here.”

Yes, well, …but I’ll find a place to put them, too.”

Let me just zip… Want some help [with that helmet]?” Cernan asked.


With my helmet on and locked, I asked, “How do you read?”

Good,” Cernan replied.

You’re a little low. I’ll turn you up,” going to the Master Volume wheel on the Audio panel below my right arm (Fig. 8.10a↓­­).

You want to do the same for me here?”

Okay,” and I turned to help Cernan with his helmet.

Get [it in place] in back, and I’ll get it in front,” Cernan suggested as we fit the helmet into the locking ring.

Watch your water [drinking valve],” I warned. This was the nipple-like valve from the drink bag inside the suit.

Okay. That water is really way in the wrong place. It’s got to be changed [later].”

You ready [for your gloves]?” I asked.

Man, that water’s way in the wrong place. Okay, yes, [cooling] feels good. …See, Jack, Ron put that [water nipple] on the snap. It’s got to be over here. That was my fault. …Okay. …Gloves, huh?”

Boy, you certainly aren’t very loud [on the intercom],” I commented.

I’m not?”

How am I?” I asked.

You’re all right. You got the volume up?”


All right. …I got my mike [closer].” With a helmet on, Cernan had to push his Snoopy Cap mike boom against the helmet to move it closer to his mouth.

Try me again. …Wait a minute. …Oh, you’re right [about the volume]…Give me a count.”

One, two, three, four, five…”

Fig. 8.10a. The forward section of panel 12 displaying the audio controls. The red arrow points to the master volume control wheel. At left, the double yellow arrows point to the VHF A & B volume controls. The purple arrow above them indicates the S-Band volume control; and the  light blue arrow to its right, the Intercom volume control. The orange arrow further right marks the VOX sensitivity control wheel. The gray handle at far left is the LMP ACA. (Base photo NASA/ALSJ/Paul Fjeld)

Okay. I’ve got MASTER VOLUME and INTERCOM full up, I confirmed (Fig. 8.10a). I think it’ll be all right. …Gene, you’ve got an empty pouch over there for this stuff, I think. We can put it on…”

Okay. Stick it behind something now and when we… Stick it up behind that rail up on top [of the cabin]. …Okay, I’m in my helmet and gloves,” Cernan said after a few seconds.

Okay. …Well, I’ll be with you shortly.” Putting on the gloves and making sure the wrist-locks were matched up took some practice in weightlessness.

I’ll do that rate gyro test [on the attitude rate gyros] while you’re doing that.”

Good.” Cernan referred to a test of gyros that could be used to show the rate of attitude changes. The test appeared in the Checklist after the Pressure Integrity Check, but could be done now and gain some time back.

A few minutes later, Cernan asked Evans about the tunnel, “Ron, is the tunnel vented yet?”

Well then, DELTA-P is still only 2.5[psi].”

Then, he asked me, “You want to put these [pens, etc.] in the purse?” The “purse” was a convenient stowage pouch that we would hang on the DISKEY in lunar one-sixth g. “Guess it’s all right for the lunar surface [one-sixth gravity] but isn’t much for orbit [weightlessness].”

[Are] they going to stay in there?” I wondered. “I can put them back in the pocket.”

No, they’ll stay there.”

Rate gyros okay?” I asked as Cernan finished the checks.

Yes. …We got the Integrity Check and prep for undocking.”

Okay. Be right with you,” I responded, and then asked, “Did you get your silicon [salve] on your hands?” Cernan’s hands tended to abrade when we worked with pressure gloves during EVA training.

I don’t need it with my IV [IntraVehicular] gloves.”

Oh, okay.”

And then I’ll read them (Checklist items) to you whenever you get that [glove] in.”

Okay, Geno, I’m verified locked [on the gloves]. How about yourself?”

Okay…and I’m locked.”

Go ahead [with the Checklist items],” I said, turning sideways to get to the oxygen distribution and other ECS controls where I could reach them easily. The cadence that developed during the reading of a checklist reassured on the one hand, but could lead to a false sense of security. Simultaneously, with the back and forth of call-outs and responses, we always needed to avoid distractions and to focus on the “why” of each switch or valve change.


PULL – EGRESS.” This action diverted oxygen flow to the suits instead of going into the cabin.


EGRESS.” This completed diverting the full oxygen circuit through the suits.


RELIEF is going CLOSED.” As this would be a pressure integrity check of the Suit Loop and not the cabin, we wanted the normal pressure relief valve in the suit loop to be closed.

PRESSURE REG A – EGRESS and B – DIRECT O2. And monitor cuff gage until we get 3.7 or 4.0.”

A is EGRESS and B – DIRECT O2.” Regulator B now supplied oxygen directly into the Suit Loop until the pressure reached the normal EVA pressure.

That’s affirm. …I’m going up [in pressure]. …And the Suit Loop’s [pressure] is going up over there, too,” referring to the gage above my eight ball and just under the array of Caution and Warning lights (see Fig. 8.9↑ for the pressure gage and C&W lights).

Why don’t you turn the window heaters on?” I asked, noticing some fogging. “Can you do that?”


My window’s still fogged up. John [Young] said we’d have to do that. Well, let’s don’t forget [to turn] it [off].” Young commanded Apollo 16 and was our Backup Commander.

Remind me to turn them off,” Cernan agreed.

Roger. …Want a little [drinking] water?”

Yes, I sure would!” The helmet had a self-sealing port through which the barrel of the water gun could be inserted. The gun delivered an ounce per squirt.

Boy, it’s (suit pressure) coming up slow, isn’t it?” Cernan observed.

Just like the simulator,” I reminded him.

I’m off the peg,” reported Cernan, watching the pressure Cuff Gage on the left wrist of his suit.

So am I. …Okay,” I said as the Cuff Gage reached the test pressure of about 3.7 psi. “Is it time [to isolate the suit loop]?”

Yes. …MARK it; that’s good.”

Okay, I’m in EGRESS [on Reg B], I said.

Okay.…Let’s monitor decay for one minute.”

Okay, I’m [starting] about 3.7.”

I’m 3.75. MARK it.”


It should be less than 0.3 [psi decay] in 1 minute. …I’m already down to 3.6. What are you?” Cernan asked.

Yes, I am too…That’s 30 seconds. How’s the cabin…I mean the suit loop [on the pressure gage]?”

Suit loop’s fine. …That was more than 30 seconds. That was a minute and [some].”

Man, I just barely passed [the Integrity Check],” I stated. Part of the loss of pressure may have been due to continued filling all the nooks and crannies of the suit.


Okay. You want me to pump it (the suit pressure) up again?” I asked.

Yes, why don’t you pump it up again to 3.7 [psi].”

Okay.” I needed to put PRESSURE REG B to DIRECT O2, briefly, to increase suit pressure and then isolate the Suit Loop, again. To be sure, I asked, “I’m supposed to go to EGRESS [now on Reg B], right?”


MARK it. What [suit pressure] you got?”

I’ve got 3.7.”

…let me give a little more [for me]” and I went back to DIRECT O2, briefly.

There’s 3.8. …Go to SECONDARY [on the CO2 CANISTER SELECT valve].”

I’m [at] 3.8.”

EGRESS [on REG B],” Cernan read from the Checklist.

Yes, it’s EGRESS.”

SECONDARY on the canister.”


Man, I still got a clump of air [in my gut]. …Now let’s monitor…” Variations in the suit pressure may have caused some additional aggravation of Cernan’s internal gas problem.

I’m about 3.55,” I noted.

Yes, that’s where I was when you went to SECONDARY.” Here, Cernan meant “EGRESS.” It was about 15:10 [on the Event Timer, Fig. 8.9↑].”

Well, they (the suits) don’t seem very tight, do they?”

That’s the entire suit loop,” Cernan pointed out.


Coming up on 50 seconds. …No, that’s (the timer) going back down – that’s 30 seconds.”

Looks like we’ve got about 0.3 [decrease] in both [canister] loops,” I said, as the first check had been with the PRIMARY canister selected.

Yes. Okay. …That’s good, Jack. Go PRIMARY on the CANISTER [SELECT].”


SUIT CIRCUIT RELIEF to AUTO; PRIMARY on the canister; SUIT CIRCUIT RELIEF to AUTO.” Cernan had backed up a step, apparently just to be sure of where we were.

Going to AUTO.”


Going to CABIN – A…B.”




PUSH – CABIN…” These last several steps reversed those we performed to do the Pressure Integrity Check of the suit loop. “Oh man! Sorry.” Twisting and reaching up behind me to get this valve, I must have passed some gas that briefly permeated the suit loop.

Okay…REGULATOR CHECK. Let’s press on with this,” Cernan said.

Go ahead,” I agreed.

Verify TUNNEL HATCH; PRESSURE EQUALIZATION; and TUNNEL VENT valves – CLOSED…They are…Ron, is the tunnel vented yet?”

It’s (DELTA-P) down to greater than 3.5 [psi].”

Well, is that vented? …We’re going to press on. That’s a big enough DELTA-P,” Cernan replied.

Yes. …that’s a big enough DELTA-P. I’m going to press on now.”

Okay, so are we. …CABIN REPRESS VALVE – MANUAL,” Cernan began. “Verify flow then [go to] AUTO.”

It’s going to MANUAL,” I responded. “…I got FLOW.”

And then AUTO.”



It’s AUTO.”

[Circuit Breaker on Panel] 16 ECS CABIN REPRESS – OPEN.” This action would prevent the automatic repressurization of the cabin during the tests.



A and B are EGRESS.”


It’s extended; it’s there.”


CABIN RETURN is EGRESS.” With all the controls now in EGRESS, we could reduce cabin pressure and check the Regulators performance when they reached their minimum pressure limit.

Can you turn around and get the FORWARD [CABIN] DUMP VALVE?” Cernan asked, referring to the dump valve on the forward hatch.

I can get the upper one.”

No. Don’t bleed [oxygen] into the tunnel – the FORWARD!”

Laughing at my slip, I said, “You’re right!”

FORWARD – OPEN and in AUTO at 4.5 [psi]. I’ll give you a call.” Normal cabin pressure is 5.0 psi.

Okay. It’s going to [be a stretch]. …Safety’s off. …Grunting, I squeezed the safety trigger on the handle and moved it to OPEN and vented cabin oxygen briefly to space.

Cernan responded with, “Suit’s going up [in pressure] a little bit [compensating for the decrease in cabin pressure]. …There’s 4.5. Okay, we’re at 4.5 and [go] CLOSED…” Cernan meant to say AUTO.

AUTO again, too.”

PRESSURE REG A to CABIN. Verify it (pressure) rises.”

A is going to CABIN. …I got a [pressure] rise.”

See it going?” Cernan asked.

Yes, [in] the Suit Loop. That’s where it should [rise].”

Wait a minute. …Wait a minute.”

It’s 4.9.”

Wait a minute…CABIN…[or] SUIT CIRCUIT RELIEF – OPEN. We should have done that. I’m sorry.” Actually, Cernan lost his place in the Checklist, and should have asked for PRESSURE REG A to go to EGRESS and then SUIT CIRCUIT RELIEF to OPEN.

Okay. I’ll go back to EGRESS [on REG A].”

Okay, go to EGRESS. [Now,] SUIT CIRCUIT RELIEF – OPEN,” Cernan said, recovering his place.


Verify suit pressure goes down to 4.5.”

OPEN and, …well, it went down, but it’s about 4.7.”

Yes, that’s because the cabin’s up there now.”

Okay, that’s good.”

PRESSURE REG A to CABIN and verify the suit…”

You want me to close the…?” For some reason, Cernan was getting me confused.

No…leave the SUIT CIRCUIT RELIEF, OPEN, verify [suit pressure rises] and then close it.

Okay. Thought so. All right.”

With the SUIT CIRCUIT RELIEF, OPEN, Cernan decided to go back a few steps repeat the REG A test. “PRESSURE REG A to CABIN.”


Verify suit pressure rises 4.6 to 5.0.”

It did,” I responded.





Then CLOSE. Let it bleed down [to 4.6]…”

Okay. It’s CLOSED.”


B’s going to CABIN.”

Did she (suit pressure) build back up?” Cernan asked.

It’s going up.”

And I can feel the flow, too [in the suit].”

Stand by,” I said as I watched the Suit Loop pressure build rapidly towards 5 psi. “Stop! You fink! …Okay. It stopped at 5.” So REG B did what it was supposed to do.


You want me to go back to EGRESS ON [REG] B? B is [on] CABIN, now.”

Cernan checked the sequence to be sure. “Stay CABIN.”

All right.”

SUIT CIRCUIT RELIEF – AUTO,” he said again.



That’s AUTO.”

PRESSURE REG A – CABIN; that should be both of them (REGs) now [in CABIN].”

Okay. They’re both there (CABIN),” I confirmed. This was their normal configuration, that is, regulating cabin pressure between 4.6 and 5.0 psi.



Cabin pressure will rise [to] 4.6 to 5.0 in approximately five minutes.”


REPRESS [circuit breaker] is CLOSED,” and that ended the Regulator Check.

Okay. The rate gyro check is done,” Cernan continued. “That [last] checked both Regulators. I can feel the flow and see it. …We got some prep for Undocking [now]. You ready?”


Go ahead.”

Cernan then read off a pruned down list of the various switch positions for S-Band, VHF-VOICE, and AUDIO desired for Undocking, while I repeated each one as I acted.


That’s [VHF] VOICE, ON, DATA, ON, OFF, and LO,” Cernan repeated. “You got that?”

Yes,” I said with some hesitation.

You don’t sound happy.”

“Well, I was happy until you said it again. …Okay,” I said, looking at the bank of switches on my right, “I’ve got [VHF] VOICE – ON, DATA – ON, OFF, and LO,”

That’s right.”



A – TRANSMIT/RECEIVE and B – RECEIVE. You get yours? Cernan had his AUDIO controls under his left arm. “You said about 10 minutes [to undocking], didn’t you, Ron? …MISSION TIMER – [SET]; Let me double check.” (Fig. 8.9↑, light blue left arrow)

Well, he gave me the time I set the [EVENT] clock on,” I reminded Cernan. (Fig. 8.9↑, light blue right arrow)

I was just checking our MISSION TIMER. …We got the TIMER – SET, counting down. OVERHEAD HATCH – LOCKED.”

Happy?” I asked.


That’s AUTO and LOCKED.”


I verified these settings and then asked, “Got a place for that?” referring to a fruit stick I had noticed in a stowage pocket.

Not right now.”

Yes, you didn’t get it [in your suit],” I laughed that Cernan missed putting his stick in the suit.

Yes, I did [put it in].”

No, I still have it,” laughing even more. “I got two pieces of it then!’

Oh!” Cernan finally figured out what I was talking about. Then, going back to the Prep For Undocking Checklist in the Activation Checklist, Cernan started with, “RATE ERROR MONITOR (COMMANDER). …Okay, why don’t you pick it up right here…”

RATE ERROR MONITOR (COMMANDER) – LANDING RADAR/COMPUTER,” I repeated, taking the Timeline Book from him (see below Fig. 8.33, yellow arrows left and right of the 8-balls).

GO.” I would have preferred that Cernan do the normal pilot thing and repeat the action requested; however, I kept my eye on each switch he set as we prepared Challenger’s displays and controls for what would be needed after undocking from America. Cernan may have been trying to make up some time as we were still a few minutes behind the timeline.


GO.” Data from the PINGS now would drive the eight ball display of Challenger’s attitude or orientation relative to the spacecraft’s three perpendicular axes.


GO.” Once we told the PINGS to accept Landing Radar information on altitude and rate of change of altitude during Powered Descent, that information would be displayed on the tape meter to the right of the Cernan’s eight ball. (Fig. 8.3b↑, large rectangular window, black with white numbers scale).


GO.” Now, a second tape meter to the right of the first would show the distance and rate of change of distance to the landing site targeted by the PINGS. (Fig. 8.3b↑, large rectangular window, white with black numbers scale).


GO.” The rate needles on the ATTITUDE MONITOR would be driven to show attitude rate changes in increments of five degrees per second.

ATTITUDE/TRANSLATION – 4 JETS,” with reference to his right Hand Controller or ATCA (Attitude/Translation Control Assembly; Fig. 8.4↑, gray handle).

GO.” 4 JETS provided maximum control authority that could be provided by the RCS.


GO.” This switch activated a routine within the RCS logic that would automatically fire thrusters as necessary to balance any directional coupling between other thrusters that might result from a commanded attitude change. Such coupling would otherwise add undesired velocity in one direction or another.




GO.” These last two actions made sure that my displays would show the same information as Cernan’s. If the PINGS ever looked unreliable to us or to Mission Control, either the LMP’s or the CDR’s ATTITUDE MONITOR could be switched to AGS mode for comparison of the two different control inputs.


GO.” The Rendezvous Radar Antenna could now be commanded to seek the America if we had to go into an Abort program during or before Powered Descent or after landing.


GO.” The PINGS would now hold a commanded attitude within the narrowest available limits.


GO.” Mode Control for these three Stabilization and Control switches (roll, pitch and yaw) put the PINGS in control of the RCS for those functions.


GO.” Similarly, these two switch positions made the PINGS or AGS, respectively, responsible for holding any commanded attitude, depending on which control system we wanted to use.

TTCA, both, to JETS.”

GO.” Any manual commands for thrust from the left-hand controllers or TTCAs (Thrust/Translation Control Assembly) would be directed to the RCS thrusters rather than to the Descent Engine.

Mount [SEQUENCE] CAMERA [on window bar]. …I need to get the Camera out.”

[We used the terms Sequence Camera interchangeably with the acronym “DAC” (Data Acquisition Camera, pronounced, “dack”) that was called out in the Timeline. Mauer had manufactured the camera with an adjustable frame-rate of 1, 6, 12, and 24 frames per second. It recorded all the Apollo landings. The undocking frame-rate was 6 fps; but for the landing I set it to 12 fps. Both frame-rates made for jerky viewings at the time; but modern processing has helped reduce this problem considerably as is evident in the examples attached to this chapter.]

Fig. 8.11. The 16 mm Data Acquisition Camera (DAC) can be seen as the black rectangular object marked by the white arrow above the LMP triangular window at right (cf. Fig. 8.2↑ for the DAC in LMS-2). Also seen is the Alignment Optical Telescope (AOT)  behind the curved tan-colored handle bar at above center. The white Interim Stowage Assembly (ISA) bag was removed during flight. The vertical tube to the immediate left of the small tag of the ISA is the removable Crew Optical Alignment System (COAS). (Base photo NASA/ALSJ/Paul Fjeld).

“Okay,” Cernan said. “Let’s do that last. …Press for now.” Actually, I just grabbed the DAC and a film magazine from their stowage location just below my right armrest and slid it into its bracket without breaking stride.

Mount the Timeline Book. We got that. Configure Circuit Breaker Panels.”

Okay, I’ll take my [Checklist] book.”

You’ve got your book.” We had two checklist books for times like this when we would be at different tasks. The last two pages had a print of the two Circuit Breaker Panels, 11 and 16, indicating which breakers had to be OPEN and CLOSED for Undocking and subsequent operation of Challenger as an independent spacecraft.

How’s your window,” Cernan asked as he got to the circuit breaker for the Window Heaters we had closed earlier due to fogging.

It’s clear.”

Okay, I’m going to pull those breakers.”

How’s your cooling? I asked. “You want it off or on?”

Oh, it feels pretty good.”

Me, too. Okay, …SEQUENCE CAMERA [breaker] going CLOSED. Got a [Power] light [on the camera]. Unlike the self-contained Hasselblad battery powered cameras, the Sequence Camera ran off LM power. “Okay, …I’ll mount the camera, …My breakers are GO. I’m about ready to put on the restraints. I don’t know about you.” I had taken the restrains off my suit when I needed to move around to get to the various ECS and hatch valves. Since then, I had used side pressure and foot placement to stay in position.

Let’s see, …CLOSED. Okay. My breakers are all okay, Jack.”

Mine are good. …‘This is the end, not the beginning,’” I read the play on words on our Mission Motto the support crew had written on the last page of the Activation Checklist. “Only the end of the Activation Checklist – the beginning of the LM Timeline book,” I editorialized. “You want me to take your Activation Checklist?”

Yes, sir.”

I need it for that camera [setting] stuff.”

[The 16mm Mauer Sequence Camera, mounted in my window, would be set at T/8 (f/8), 1/250th of a second shutter speed, and six frames per second, and I ran it for about one minute to be sure it was ready to film undocking and separation from America. The 70mm Hasselblad camera would be set at f/11 and 1/250 for hand-held photos.]

Okay, Ron,” Cernan called. We’re at 5 minutes now and counting [down to undocking]. How does that sound?”

Yes, I’ve got 6 [minutes].”

Well, we better go on your time. Better check your undocking time. If you’re using 110:27, it’s 5.

[Undocking at 27:]55.”

Oh, you give me a hack at 5 minutes, then, will you?”

Okay. Stick it in there. …5, 4, 3, 2, 1, MARK it!

We’re with you, and your attitude looks good here.” That attitude was zero roll, 180 pitch, and 060 yaw for Challenger.

Wish I had a tissue,” I commented as I saw that some dust particles had adhered to my window.

Ron,” Cernan added, “when you get all squared away, we need another NOUN 20. …On my Mark.”

Go ahead.”

3, 2, 1, MARK it!”

[These simultaneous readings of the yaw, pitch and roll angles in the Inertial Coupling Data Unit (ICDU) in the PINGS would give a measure of the relative drift in the two spacecraft guidance systems when compared with those we recorded after the up-coming P52 star sightings and subsequent fine alignment of Challenger’s guidance platform.]

Okay,” and Ron rapidly began to read off his NOUN 20 guidance platform angles.

Wait a minute, Ron. We’ve got to copy them.” Cernan complained. “You didn’t give us a chance.” Trying to write his numbers down, I had lifted my arms in frustration.

Say again?”

We’ve got to copy them! Slower!”

Okay. R1, 000.35…; R2, 104.70…; R3, 000.52…. How’s that?”

We got them.”

[Ours are]…Jack, [let me see them…], 301.09…; 284.50…; and 359.48…And that was at 110:29:00.

I got it,” I replied after recording both NOUN 20s on the first page of the Timeline Book.

Okay, Ron, that puts us inside two minutes, and we’re ready.” Cernan put the computer into P47 to monitor any velocity changes caused by undocking.

We’re all set over here.”

Would you believe I tried to blow the window [particles] off,” I said with a chuckle, as I had my helmet on.

I’d get you a tissue, but it’s too hard to get at right now. …we’re 2 minutes away.”

I got the big ones off.” These were dust particles that might degrade some pictures.

They’re down here, if I can. …Well, it would take too much to get in that box.”

Don’t worry about it.”

My COAS even works,” Cernan commented as we waited for Evans to cut us loose.

[COAS stands for Crew Optical Alignment Sight, and it provided an ingenious, backup manual means for obtaining range and range rate during a LM-active docking with the CSM, if required. As it was aligned with the LM gyro platform, it also could be used to get a coarse alignment of the PINGS as was needed on Apollo 13. Normally, the COAS was mounted just above the left hand window of the Challenger; however, for a manual docking, it would be mounted in the Overhead Window, above the CDR’s crew station.]

Ron, I called, “remember, as soon as it’s convenient, you’ll start your maneuver to SEP attitude, and I’ll try to get a good picture [of America].

We got the Hasselblad handy?” Cernan asked. Then, “I forgot to look up at you [through the overhead rendezvous window]. It better work! Get some pictures of us.”

Son of a gun! Sorry about that.” Evans had almost forgotten about taking pictures.


Challenger’s hanging on the Probe. You should be hanging on the Probe. …You are,” Evans told us.

We are,” I acknowledged.

…at zero [on the clock], we’re backing off.”

Sure [wish] we could get some pics [of this from outside].”

Check your [film] magazine, when you get a chance.”

Here we go!,” Evans called.

We’re backing off. We’re free!,” Cernan confirmed, watching out the overhead window. Talking to me, he said, “Oh, is he beautiful! You want about 1/250 and f/11 or 8. What’s your focus?”

About 50 feet.”

Get ready to…”

Fig. 8.12. View of America above the lunar surface as seen through the overhead docking window above the CDR’s head soon after undocking of the two Apollo 17 spacecraft. (NASA Photo AS17-147-22452).

I’m going to go [with the DAC],” I said.

Hey, guess what?” Cernan asked. “Did you have [VERB] 77 in there?”

Yes.” This entry, which I had loaded ready for entering immediately after Undocking, would set the Rate Command/Attitude Hold Mode in the Digital Auto Pilot (DAP) so that Cernan would have that control mode after Undocking.

I did that. [But] I took it out,” Cernan said. “I took it out after copying the P47 velocity residuals after Undocking.

Okay.” I am not sure why he did this, but the Checklist called for it the first thing after Undocking. The Checklist also called for putting the PINGS in idle (P00) and entering a VERB 60 so that he would have Attitude Rates on his eight ball’s error needles. Belatedly, Cernan re-entered VERB 77 and began the maneuver necessary to view America. I then entered P00 and the VERB 60.

I want a YAW left [to] 60.” This and a Pitch Up to 90 degrees would give us the view we wanted for pictures of America. Loud bangs accompanied these maneuvers as the shock of RCS thrusters firing came through to the cabin.

I think we know when they (thrusters) fire,” I said, unnecessarily.

You’ve got your VERB 60 in there, too?” Cernan asked.


You look beautiful, Ron…”

Yes, so do you!” (See Fig. 8.13)

Fig. 8.13. Command Module view of Challenger shortly after undocking. The docking hatch is quite visible centered on the top of the LM; and the target the CMP in America will use for alignment during the later rendezvous is seen as the smaller white and black concentric circles to the right of the hatch. The overhead window that the CDR uses in the initial alignment of the LM for docking is the blue rectangle surrounded by the black frame to the right of the rendezvous radar and above the ladder on the forward landing gear strut. The CDR has to look above his head to see through it. Cernan took the picture of America shown in Fig. 8.12↑ through this window. (NASA AS17-151-23199).

Fig. 8.14. View of Challenger as seen from America shortly after backing off from the aspect seen in Fig. 8.13. In addition to the Ascent and Descent Stages, Challenger’s two windows, rendezvous Radar, S-Band Antenna, two Quads of RCS thrusters, the Front Hatch, and the ladder on the front landing gear strut are visible. (NASA Photo AS17-151-23201).

You need to yaw left just a little more. …Well, you can do that when you get up there [in pitch].”

Oooh, boy, give me a VERB 76.”

You got it.” Cernan wanted to go to Minimum Impulse in the DAP.

Are you beautiful!”

What’s wrong with my [DAC] camera now?” I complained as the ON light went out.

Well, I don’t know but…”

Come on, you stupid thing!,” I yelled while tapping the body and film magazine, my initial solution to almost everything.

I can see it occasionally working, Jack. It’s the mag. I see it (the ON light) blinking.”

You’re pretty out there, you know that?” Evans enthused.

Try and get some 70 millimeters [pictures], Ron,” Cernan requested.

Okay. That’s what I got.”

Okay, it’s (the DAC) going,” I noted, finally. (A 6:32 min DAC video of the undocking sequence can be viewed here.[30] America appears at the 25 sec mark. If downloaded, the file size is ~103 Mb.)

I’ve also got some 16 millimeter action,” Evans added. (A 4:12 min clip of Ron Evans’ film sequence without audio can be viewed here, also provided by Ben Feist. If downloaded, it is ~63 Mb in size. Figs. 8.13↑, 8.14↑ are enhanced Hasselblad images with improved visibility of the LM)

Great!,” Cernan exclaimed. “We got all our landing gear?”

I’m maneuvering now [to look],” Evans replied.

Ron, have we got all four landing gears,” Cernan repeated, not hearing Evans’ last transmission. Then, looking at the Timeline, he said to me, “Go to VHF ANTENNA – FORWARD.”

It’s FORWARD,” I confirmed, having already made the switch when I went through the post-Undocking list of actions called for. Some of Cernan’s questions during this period show how occasionally he would forget who would do what that we previously had worked out in training.

Again, “Ron, have we got all four landing gears?”

You look great.” It is always good to confirm and confirm again when you have a chance; but, earlier, all the sensors on the telemetry had convinced Mission Control that all four gears had deployed properly and we had a safe Landing Gear flag indication in the cabin. The Gear needed to be fully locked to activate the sensors.

America came into view from my window, and I said, “Okay, I’ve got him.” (i.e., the 25 sec delay in the appearance of America in the video clip linked above).

[You have what looks like a] flow [of] water,” Evans observed, “but I guess it’s supposed to be that way, huh?”

That’s right,” Cernan said, referring to the vacuum-induced ice particle mist from the cooling system’s sublimation vent.

…Beautiful,” Evans repeated. “Now, the Sun’s shining right through the window. That’s the last picture I’m going to get of you.”

Is that too far down?” Cernan asked me relative to his pitch attitude.

A little bit. I’m getting him though. Tell him I’ve got a good shot of him.”

Your SIM BAY door jet[tison] looks clean,” Cernan told Evans.

Very good. …You’re right in the Sun for me. You should be getting some good pictures of me.”

We’re working at it, partner.”

Thank you.”

Back to business, Cernan read, “SEQUENCE CAMERA – OFF; HELMET AND GLOVES – OFF; SUIT GAS DIVERTER – EGRESS…,” and I complied. “How’s our cabin [pressure and O2 flow]. Look pretty good to you?”

Yes, sir, it looks great.” I replied.

Isn’t that something? America, you look ‘beautiful’,” Cernan paraphrased the well-known song.

Jack, I’m going to go through these steps and take my helmet and gloves off.”

Okay. I’ll get him over this crater and then [do the same]”

Fig. 8.15. Cernan’s photo of America over Becvar X, located at ~124°E, 1°S on the lunar far side, a 26 km diameter crater near the NW wall of Becvar Crater. (NASA photo AS17-147-22453).

Hey,” Evans suddenly called, “there you are! Out the hatch window.” America had rotated so Evans’ view had changed and we had left the direct line into the Sun.

Tell him to wave to us,” I suggested, laughing. “Oh, that’s a neat shot right now!”

Boy, that is. Did you get that one?”

Yes.” (See Fig. 8.16)

Fig. 8.16. America is rotating from the view in Fig. 8.15 so that now the CSM has presented a broadside view with the SIM BAY in the Service Module just visible at the lower right of the spacecraft. America is near an irregular crater, at ~117°, 1.5°N, ~17 km in long dimension, abutting the north wall at right of Abul Wafa on the lunar far side. (NASA photo AS17-147-22457).

…Look at that SIM BAY. Hey, we can see you out the window, [Ron]. …Boy, that is some shot.”

I think I’ve used 50 percent [of this DAC film magazine]. I better stop. …Okay, Ron, you’re off candid camera.”

Okay. …Good show.”

Then, I saw one more thing to photograph— the nozzle of America’s main engine, the Service Propulsion System (SPS). “I’m going to get that Engine Bell.”

[And] make your darned landing, now,” Evans added. “Okay?”

Oh, I forgot to say goodbye to you, until we see you in a couple of days,” Cernan said. “Don’t forget, no TEI updates.” Cernan referred to Evans leaving the Moon (TransEarth Injection) without us.

Don’t worry,” Evans laughed, “never happen.”

We’re moving to look right up your [engine] bell,” Cernan informed Evans.

I turned it (SEQUENCE CAMERA) back on, Gene.” (The rotation of America to an end-on position occurs at the end of the DAC video linked above. Cernan’s Hasselblad view is in Fig. 8.17, below).

Fig. 8.17. America continues to rotate, presenting the SPS and engine bell towards us. The spacecraft is above the south wall of Firsov at ~113°E, 3.5°N on the lunar far side. The crater itself is ~51 km in diameter. (NASA photo AS17-147-22460).

Yes, I’m still getting him [with the Hasselblad], too.”

Remember: Falcon 179,” Evans said.

109,” I corrected.

109, Ron, that’s what you are, Babe,” Cernan agreed. “109; Falcon 109.”

[Navy pilots, such as Evans and Cernan, used Falcon codes to transmit comments or disagreements quickly that otherwise might not be appreciated by superiors. “Falcon 109” is said to have meant “That God damned SOB,” so I am not sure who was being referred to by this interchange. After reading chapter 26 in Cernan’s book, The Last Man on the Moon, it might have been that the two of them were referring to me, and the fact that I had replaced Joe Engle on the original Apollo 17 crew (see Chapter 2). On the other hand, after 15 months of training as a crew, one would think that this was no longer cause for resentment.]

Fig. 8.18. America is approaching the 25 km diameter crater Firsov T, located at ~109°E, 4°N, ca. 90 km from the previous photo position. (NASA photo AS17-147-22461).

Man,” Cernan continued. “What a beautiful engine bell! I just forgot. …We’re up here swinging all by ourselves.”

Yes,” laughed Evans.

Fig. 8.19. One last look before America drops to an even lower, faster orbit. The spacecraft is passing Firsov T at left, and is approaching the bright 22 km diameter crater Firsov K, located at ~108°E, 4.5°N. The bright arms from the western and north-northeast walls are reaching towards the southern wall of the crater Al-Khwarizimi J, ~19 km away. (NASA photo AS17-147-22462)

We better do something; like get ready?” I reminded everyone.

Yes,” Cernan responded, looking at the Timeline, again, “we’re in good shape. Landing Radar Checkout’s next.”

Is that all,” I said, a little facetiously, knowing that we had a lot left to do.

We’ll pick it up right here. Only got… Oh, yes,” Cernan finally looked ahead in the Timeline. “Well, we’re a little behind, I think,” he admitted.

Why don’t we go ahead,” I suggested. “I can leave that darn thing (DAC) running [while America’s in view]. We’ve got an extra [film] mag. …I’m going to go back to f/11.”

There went another screw [in the cabin]. More screws coming out now. …Oh, [looking] right up his tailpipe (Fig. 8.18). …Got a place we can set this? Isn’t there a piece of Velcro here, somewhere like that.”

I can put it (the screw) over here in a minute.” No matter how careful Grumman personnel had been in the construction of Challenger, a few screws and other small items would get lost in the cabin. Once we began to maneuver the spacecraft, these gradually became dislodged and would float around until we captured them.

It’s on Velcro. Okay, Jack, SUIT GAS DIVERTER – EGRESS.”



DIVERTER is EGRESS; RETURN’s EGRESS…” These valve positions put oxygen flow continuously through the suits and helped to keep them dry. “I don’t see any Velcro for my helmet, but…” During the previous discussion, we finally finished taking off our helmets and gloves. They would go back on when we prepared for Descent and Landing in Taurus-Littrow.

Landing Radar Checkout

The big thing is the Landing Radar,” Cernan said again, apparently thinking of what had to be done before we had communications with Mission Control on this orbit. After that, we also needed to take care of a Descent Engine Throttle Check, Descent Engine Pressurization and Checkout, AGS Activation and Control Check, Rendezvous Radar Checkout, and so on, a problem with any of which could keep us from landing on the Moon.

This is where we are,” pointing to the left side of page 1-1 of the Timeline book. “Of course, this won’t tell us much, but, …Ron, you sure are pretty.” Cernan was having trouble getting his focus back on the job at hand.

Well, the old LM Challenger looks good there, too,” Evans acknowledged.

The main thing was we had four legs, huh?” Cernan’s sensitivity to the landing gear remained, in spite of all other indications. Maybe he recalled a bad experience with a past bad deployment of an arresting hook during a carrier landing.

Can you see the SIM BAY at all?” Evans apparently had not heard our previous comments.

Yes,” Cernan replied. “We saw the SIM BAY – almost oblique – but saw the whole thing. We’re looking right down your tailpipe at the surface [of the Moon].” (See Fig. 8.18↑)

Okay,” I prompted, again, “Landing Radar Check…”

Okay, Jack,” Cernan began going down the Checklist.

LANDING RADAR breaker is IN (CLOSED), and I’ve got [the] altitude and velocity transmitter. That’s a good start.” Here, Cernan referred to movement on the Altitude and Altitude Rate tape-meters next to his eight ball.

Fig. 8.20. The white arrow on panel 1 points to the Altitude (white numbers on black) and the Altitude Rate (black numbers on white) within the wider of the two rectangular-shaped instruments to the right of the eight ball. (Base photo NASA/ALSJ/Paul Fjeld).

[The absolutely essential Landing Radar system resulted from the combined efforts of engineers from Grumman, NASA’s Manned Spacecraft Center, and Grumman’s subcontractor, Ryan.[31] The system consisted of a three-beam Doppler radar that could determine altitude, rate of descent or change in altitude, and horizontal velocity in two axes. The velocity sensor operated at 10.51 GHz and the altitude sensor at 9.28 GHz. Mounted on the bottom of the Descent Stage, the radar could assume two positions, one for the early phase of Powered Descent when Challenger would be on its back and one after we pitched forward so that the landing site became visible through the windows.]

[Landing Radar temperature is] 80 degrees. That’s okay (limits 60-90 degrees),” Cernan began. CROSS POINTERS – HIGH MULTIPLE.” Just above and to the left of the 8-ball (FDAI – Flight Director Attitude Indicator, see Fig. 8.21 below), he could see a display of cross-pointers that would provide a comparison of the rate of change of Elevation vs. Forward Velocity and the rate of change of Azimuth vs. Lateral Velocity. During Powered Descent with Landing Radar active, the planned trajectory would be to keep these cross-pointers centered on zero, that is, with the four variables optimized.

Fig. 8.21. The cross-pointers for both the CDR and the LMP are marked by the white horizontal left and right arrows in panels 1 and 2, respectively. The vertical and horizontal black stripes within the windows move with respect to each other as a function of the variables mentioned in text. (Base photo NASA/ALSJ/Paul Fjeld).

You reading me alright?”

Yes, I’m just getting organized here [on my side],” I answered. On the other hand, I was watching that nothing was skipped in the Checklist.

MODE SELECT – LANDING RADAR.” This would be the switch position for the upcoming test, but MODE SELECT would be at the PINGS position for Powered Descent until the Landing Radar data could be verified. After verification of its accuracy, Landing Radar data would be used instead of the PINGS’ less accurate knowledge of the Challenger’s altitude and velocities relative to the landing site.

Where’s my Velcro [patch on the panel]? No Velcro, huh?” I am trying to get everything, helmet, gloves, camera, etc., tied down for the time being.

Should be right there,” Cernan said, pointing to its normal spot.

Oh, there it is.”

Just put it on that corner. It’ll stay. …Boy, I’ll tell you, every time you float around you knock something off over here.”

I’m going to get on my restraints, here, Gene.”

As we finally got better organized, Cernan repeated, “MODE SELECT – LANDING RADAR. Tape meter [RANGE/ALTITUDE MONITOR switch] – H and H-DOT.” H and H-DOT meant Altitude and Altitude Rate were selected rather than Range and Range Rate that would be used in conjunction with the Rendezvous Radar.

H-DOT. I’ll read it (the Timeline),” I said.

Okay. Go ahead.”




Cernan interrupted, again. “You put the camera away, didn’t you? Oh, that’s alright.”

What have you got [visible]?” I asked, referring to Ron and America.

…that’s alright. I got that picture, anyway. …Okay. RADAR TEST – LANDING. You ready?”

POWER SIGNAL LIGHT – OUT.” No light meant that cross-pointers had power. This is a small light just above both sets of cross-pointers that I was used to relying on in simulations to catch whether SIMSUP had failed the power going to the Radar.

It’s out.  …It is, now.”

Well, it went out when you [went to TEST]?”

No, it didn’t. It was still on, Jack.”

Was it?”


Well, I couldn’t see it.” The light had been visible to me in training in the Lunar Module simulator.

Yes, it was way back in there.” If Cernan were right about the delay in the Power Light going out, it suggested that something delayed power getting to the cross-pointers and this might indicate some other problem.


They are.”

Tape meter H (Altitude) should go to 8,000.”


And H-DOT (Altitude Rate) to minus 480 [fps].”


VERB 63 NOUN 12, OPTION 2 [PROCEED].” This computer entry started the PINGS test of the Landing Radar.

As Cernan entered this on the DISKEY, he commented, “The trouble is the Landing Radar Test won’t tell us anything about that transmitter [and receiver].” He is referring to the components of the Radar that actually will measure Challenger’s altitude and descent rate during the landing sequence. This test, however, would cover the rest of the electonics.

That’s all right. We’ve got to do it (the test),” I replied.

Yes. It’ll tell us something,” Cernan agreed. The test verified that the PINGS and the Radar communicated properly – an important thing to know.

VERB (NOUN) 66 [display] is what?” I meant NOUN 66 that displayed the test for Slant Range and Antenna Position on the DISKEY.

8287[feet] and ANTENNA POSITION.”

That’s good…Position 1 [is good]. …PROCEED.” The display corresponded to the numbers and position stated in the Timeline.

Okay. …[NOUN] 67 – minus 495 [for Vx]…”

That’s good.”

…plus 1862…

That’s good.”

…plus 1331.”

That’s good.”

PROCEED?” Cernan asked.

Yes. …Well…no, no, VERB 34. …Uh-oh,” as Cernan had already hit PROCEED. This illustrates what can happen when checklist discipline breaks down. Cernan should have waited for me to read the next line instead of assuming that it would say “PROCEED”. I, in turn, looked up and spoke too quickly with a “yes”. In this case, it did not make a difference as the VERB 34 entry was to stop the PINGS test.

That’s alright,” Cernan assured me. “That just said it (PROCEED) wasn’t an LGC (LM Guidance Computer) [function]. That’s just [to] say ‘defer a Lock-on [of the Radar]’. That’s alright.”

Okay. …RADAR TEST [switch] – OFF.”


ALTITUDE [on tape meter] goes to zero. POWER SIGNAL [LIGHT] – ON. CROSS POINTER’S – CENTERED. …I’m not going to able to see that POWER LIGHT.” I mused. “I’ve used that [in the simulator] to tell me when the Radar dropped in and out. …Okay. Read that again.”

CROSS POINTERS are CENTERED,” Cernan confirmed.

And the LIGHT’s ON, and we went to zero [on the tape meter.]”

But H-DOT didn’t [go to zero],” Cernan said. “Altitude did.”

No, it (Checklist) didn’t say anything about H-DOT,” I pointed out.


PINGS: LANDING RADAR circuit breaker – OPEN,” I continued.

Breaker’s open, and my power [Radar signal strength] went to zero.”

Okay, we’re a little late,” I reminded him.

Okay. Let’s pick it up.”

Matter of fact, we ought to just about have AOS. And I’m FORWARD [on the S-BAND ANTENNA].”

You can pick up your camera [settings] when you want…”

Okay. We’ve got them (Houston),” I said, noting that the S-Band meter showed signal strength in the uplink carrier.

“Hello, Houston.” Cernan called. “Do you read Challenger? …Hello, Houston. If you’re reading Challenger, we are undocked, and we are GO.”

“Challenger, Houston; very, very weak. Over.”

“Challenger undocked on time. We are GO. Landing Radar Checkout is complete, and it is GO. And we are looking at America, the Beautiful.”

“Okay, Geno,” Fullerton said. “I understand you’re undocked. But we’re not reading but about 10 percent of what you’re saying. Stand by.”

Let me go to the HIGH GAIN [Steerable Antenna],” I said.

“Hey, Geno, I want to pass this on to you…”

“I’ll wait until you get HIGH GAIN.”

Give me those [Timeline] angles, again,” I requested.

Should be [plus] 9 and minus 37. …How about 6 and minus 29. …6 and minus 29.” Cernan had entered NOUN 51 in the DISKEY to get Steerable Antenna angles as we had maneuvered out of the attitude for Undocking in order to view America.


[Now, try] 5 and minus 28.”

It’s (antenna lock) not going to hold yet.” I reported.

She’s not holding yet?”

“No,” I stated. “Houston, this is Challenger. Won’t hold on the Steerable Antenna, yet. It looks like I’m getting oscillations in my up-link signal strength, and then it gradually drops off to zero.”

While I worked to optimize communications, Cernan started the Descent Propulsion System Throttle Check. “On [panel] 16, STABLIZATION/CONTROL: ENGINE ARM –CLOSED.” This circuit breaker is on my panel, but, as I did not respond, my work on the antenna apparently kept me from hearing Cernan’s call.

“Okay, Jack. We’re reading you better now. Understand.”

“Okay, Gordo,” Cernan began again. “If you’re reading, you got the word. We are undocked. Landing Radar Self Test was GO. We’re ready to press on to the DPS Throttle Check, and we’ve been looking at America, the Beautiful, in rare form.”

“Okay, Geno, we got that. It sounds good.”

“And the [velocity] residuals on P47 at undocking were zero, minus 0.1, and zero [for x, y and z].”

“We copy that, and we’d like you to try the Steerable Antenna again,” as if I was not doing just that.

Here’s your [NOUN 51] angles, Jack; zero and minus 30.”

There it is!,” I exclaimed after going to those angles. “Houston, we got it”

“You sound real good. Loud and clear.” Merritt at the LM TELMU console in the MOCR was happy.

“Let me give you some NOUN 20 angles [at Undocking],” I responded, “if you want them.”

“Go ahead. Ready to copy.”

“The LM: plus 301.09, plus 284.53, plus 359.48; CSM: plus three zeros 35, plus 104.67, plus 000.52. The time, 110:24:00. Over.”

“We got that.”

Descent Propulsion System Checkout

“Gordo, we’re ready; DPS Throttle Check. I’m ready to hit ENGINE STOP.” This meant that Cernan had put the two THROTTLE CONTROL switches just below his eight ball to MANUAL and COMMADER, respectively, and that both our TTCA levers had been moved from JETS to THROTTLE (MINIMUM).

Fig. 8.22. The throttle control switches are the top two marked by the red arrows in the Engine Thrust Control box outlined below the eight ball of panel 1. The lower switch marked by the yellow arrow at lower left is the engine arm switch (see below). (Base photo NASA/ALSJ/Paul Fjeld).

[The Descent Propulsion System (DPS, pronounced “dips”, of course, would be the rocket that would reduce our orbital velocity until the Challenger’s orbit would intersect the floor of the valley of Taurus-Littrow and then give us the propellant reserves necessary to maneuver to a safe spot to land. Space Technology Laboratories, after a competition with Rocketdyne that ended in 1965, designed and manufactured the variable thrust (throtteable) DPS on which every Apollo lunar landing depended. As with the Ascent Engine and the RCS, hypergolic Aerozine 50 fuel (a 50/50 mix of hydrazine and unsymmetrical dimethlhydrazine) and nitrogen tetroxide oxidizer propelled the engine. A system of tanks, regulators, and heat exchangers provide Helium pressurization on the fuel and oxidizer bladders in the tanks. Except for the Supercritical Helium pre-heater for propellants, the fuel injector ring, and the engine nozzle, components with essentially no risk failure, the DPS’s critical components were fully redundant.[32] ]

“Stand by. …Okay. We’re ready,” Fullerton said, having checked with Thorson across the MOCR’s rows of consoles.

Cernan also had placed the ENGINE ARM switch to DESCENT that triggered an expected Caution Light for the DESCENT propellant pressure REGULATOR as the system had not been pressurized, yet.

“And the [REGULATOR CAUTION] LIGHT is ON,” Cernan reported and then said to me, “Why don’t you pick them (the Timeline items) up here.”

Okay. ENGINE ARM – ON [DESCENT].” (Fig. 8.22↑, switch in down position).

MASTER ALARM.” (Fig. 8.23↓)

You got it?” I was asking if Cernan was going to turn the Master Alarm light off. With any red MASTER ALARM light, the procedure was to punch the light immediately to turn it off so that it was reset for any other problem. As he did not respond, I punched the MASTER ALARM light off.

“The REG [CAUTION] LIGHT is ON,” Cernan repeated.

TTCA – MIN[INIMUM],” I continued. In the centered detent in his left hand controller, the right, COMMANDED side of the Thrust Meter above Cernan’s eight ball should show between 6.6 and 13.4%. The left side of the Meter showed actual ENGINE Thrust, but, of course, this would read zero during the Throttle Test.

Fig. 8.23. The white arrow points to the thrust meter above the eight ball on panel 1. There are two scales within the instrument. The left side is the actual thrust, and the right side that commanded at a given time. The red arrows left and right of the eight balls on panels 1 and 2 point to the Master Alarm lights. (Base photo NASA/ALSJ/Paul Fjeld).

You should be…”

11 percent.”

That’s good. …Then soft stop [up].” This upward soft stop on the TTCA should show between 46.2 and 59.2% on the Thrust Meter.


That’s good; [now,] MAX.” The full throttle position should show between 93.6 and 100% on the Meter.

“Roger. We’re showing the ENGINE ARM Circuit Breaker may be out. Would you check that?”

ENGINE ARM [Circuit Breaker] is OUT?” I queried Cernan. “Oh, you missed that.”

I know. I thought you said ‘yes’.”

No, I’m sorry, I didn’t hear you.” From the transcript, it is clear that I had been working with Fullerton on getting better S-Band communications. Cernan had read out loud that line in the Timeline, but he had not confirmed that I had performed the action. Again, discipline, discipline, discipline!

Oh, I thought you gave me ‘affirm’ on that.” The transcript contains no response to Cernan’s call-out; just my continuing conversation with Fullerton.

“I’m sorry, Gordy,” I responded. “A little …We missed that here. Okay, we’ll try it again.” I pushed in the circuit breaker.

No, I don’t want to do that. Okay?” Cernan said. He did not want to go back to the beginning even though that just meant cycling the ENGINE ARM switch to DESCENT again and quickly re-running the TTCA checks. On the other hand, telemetry related to the throttle checks was not dependent on power from this circuit breaker, so Thorson had seen the results of the tests. I did not realize this at the time, and I doubt if Cernan did either, so not re-running the tests bothered me.

Okay. Go ahead [with your TTCA, again], I said. “That’s good [at centered detent]. Now to Soft Stop. …Okay. …Max. …Adjust the friction?”


My turn?” I asked.

Yes. …Let me give you the LMP [on the MANUAL TROTTLE switch].”

You got it [switched]?”

Wait a minute. …You got it now.”

That’s good,” I said as I went through the three TTCA positions and check the COMMANDED thrust on the Meter. “It’s good. [Leave control] with me or you?”

[I never really understood this test of my throttle controller. Had Cernan’s left hand TTCA controller failed during descent, he could reach over and use mine with his right hand, although I do not recall that we were ever given this failure in simulations. Such a failure, however, would have been cause for an Abort. It would have restricted his ability both to use his Landing Point Designator and use his right controller with his left hand to fly to a safe spot for landing. It also would have blocked my view of the DISKEY and prevented providing needed verbal readouts as to actual altitudes, altitude rates, and horizontal velocities that allowed Cernan to concentrate on looking out the window for the spot where the PINGS would land us if he took no further action. It is possible that this test was really focused on a failure of the Commander’s TTCA during a LM-active rendezvous when there would have been no choice but to use the LMP’s TTCA. A landing alternative that I practiced on my own in the simulator consisted of me flying the necessary Altitude-Altitude Rate profile based on the PINGS incorporation of Landing Radar data with Cernan flying a trajectory to the landing site by re-designating the PINGS guidance with his right hand controller while asking me for changes in Throttle settings. It is not known whether any Apollo Commander would have used this alternative even if not doing so meant not landing on the Moon. Certainly, during Apollo 15 training, Dick Gordon specifically said that he would not let me land the Lunar Module (we were the Backup CDR and LMP for that mission) and in one Apollo 15 simulation, pushed me out of the way so he could try to land without his hand controllers.]

My [Throttle] friction’s stiff,” Cernan reported

So is mine. …Okay,” I said after adjusting the Friction Knob.

“Gordy,” Cernan reported, “if the Throttle Test looked okay, I’ll go ENGINE ARM – OFF.”

“It looked real good,” Fullerton said, presumably after hearing Thorson’s “Looks good, Flight”, report on the MOCR comm loop. “Go ahead.” Again, I was surprised at this reaction from LM CONTROL, as I thought they had not seen the results of the TTCA tests.

With the ENGINE ARM, OFF, I went to the next step: “Back on the CWEA (Caution & Warning Electronics Assembly) [circuit breaker]. That’s [CYCLED and] reset.”


ENGINE STOP –RESET.” This was a push button switch on a panel in front of Cernan, between his hand controllers, that could be reset by pushing it.

Fig. 8.24. (Lower left) the CDR’s TTCA hand controller (gray); his yellow left hand grip (middle); and the stop/start and reset push button (right). The gray housing behind the latter is the safety guard for the push button (NASA/ALSJ/Paul Fjeld).

Okay. You got [the CAUTION] lights out.”

THROTTLE CONTROL – AUTO and COMMANDER.” This change put automatic control of the Descent Engine thrust back to both the PINGS and manual override control to Cernan in preparation for Powered Descent.


TTCA (both) to JETS.”

And I’m JETS,” Cernan verified.

Okay, [so am I].”

Descent Propulsion System Pressurization and Checkout

Why don’t you give me the readings [for Descent Engine pressurization from the Timeline],” Cernan requested.



Okay, [first], PROPELLANT to MONITOR…DESCENT 1: the temperature is about 67, both sides [fuel and oxidizer]. I read these values off a meter to the right of the Thrust Meter mentioned earlier. (Fig. 8.23↑, instrument immediately to the right of the thrust meter marked by the arrow, i.e., the middle one).

Both GO.” 50-75 degrees was the acceptable range.

Pressures are about 75…make that 85 and 75 [psi]…” Acceptable range was 30-80 psi. (rightmost of the three meters in that row in Fig. 8.23↑). 75 psi was the correct reading as the two tanks had the same pressure sensor (see below).


And the temperature [of DESCENT 2] is about 68.”

That’s good. Oxygen?”

Yes, those pressures won’t change, because it’s [reading] the same transducer. They didn’t change.” For reasons unknown to me, each pair of fuel and oxidizer tanks had a single pressure sensor, but redundant temperature sensors. Possibly, it had been worked out that if a pressure sensor failed, the temperature measurement as well as engine performance would give sufficient indication of whether a significant problem with tank pressures existed.



1260…Those are both GO,” I said.

[The Ambient Pressure readout gave us the pressure in the main storage tank of Helium needed for continuing pressurization of the fuel and oxidizer tanks. Supercritical Pressure gave us the pressure in a second helium tank, essentially a start-up tank, kept at supercritical temperatures and pressures (when Helium behaves neither as a pure liquid nor a pure gas). During engine operation, the pressure in this second tank was maintained by exposing it to a heat exchanger through which warm fuel was flowing. At Engine Start, Supercritical Helium flowed immediately through a pressure regulator and into the bladders lining the fuel and oxidizer tanks. During engine operation, Helium for continuous pressurization came from the main “Ambient” tank.[33] ]

What else you want?” Cernan asked.


Talkback gray…[REG] 2, BARBER POLE,” as required, we kept Regulator 2 off line to make sure Regulator 1 performed as expected. “GRAY” on the talkbacks indicates a proper operation and “BARBER POLE” indicates the function is inoperative.

Fig. 8.25. The Descent Helium Reg 1 and Reg 2 switches are at the bottom middle of panel 1 marked by the yellow arrows, respectively. Their corresponding talkback indicators are immediately above each one. (Base photo NASA/ALSJ/Paul Fjeld).

“Okay, Gordy,” Cernan called. “The MASTER ARM is coming ON.” This is to arm the two redundant systems of explosive devices that would open Helium pressurization lines to the Descent propellant tanks.


Why don’t you read them (Timeline items) to me?” I suggested.

MASTER ARM – ON. I got two good lights [on the two explosive systems],” Cernan continued.


“Two lights,” acknowledged Fullerton.

“Okay, on my Mark…DESCENT PROPELLANT ISOLATION VALVE, 3, 2, 1, MARK it. We heard it [fire].”

We got a jar in pressure [in the propellant],” I observed.

Yes, I don’t doubt that. …What’s the next one?”

“Gordy, there was a slight, …upward fluctuation in pressure in the [propellant] manifold when we fired that,” I reported. “It’s back to where it was pre-firing.”

“That’s what it should have done, Jack,” Fullerton said after getting the word from Thorson at LM CONTROL. I just laughed at my unnecessary observation.

Let’s go,” Cernan pushed, finally acting impatient.


“3, 2, 1, MARK it. We got it.”

Hear that stuff gurgle,” I commented with a laugh.

Yes, that’s good. The thing (Challenger) is coming to life, Jack.”

“Looks good on board!” I exclaimed to Fullerton. “About 240 [psi], both sides…”

“Looks good on the ground.”

MASTER ARM – OFF,” I reminded Cernan.


“Say, Gordy,” Cernan joked, “this thing sounds a little bit like my stomach sounded a couple of days ago.”

“Roger, there.”

Checking the Helium pressures, I noted, “AMBIENT PRESSURE 520 and stable.” This was down 1100 psi as a result of propellant pressurization. “SUPERCRIT is 1260, still.”

You happy?” Cernan asked, again.

Yes. Very happy!”

AGS Activation

[TRW designed and developed the Abort Guidance System (AGS) as a backup guidance and control system, primarily for use to abort a landing in case of a failure of the PINGS during Powered Descent and landing[34]. The AGS consisted of a strapped-down, inertial-sensor package and an open-loop programmer powered by a digital computer of 4096 words, half erasable and half hard-wired. The DEDA keyboard allowed me to communicate with this computer, but, unlike the PINGS, Mission Control could not communicate directly with the AGS by telemetry, although updated PINGS guidance information could be transferred electronically onboard between the two guidance systems. The design parameters for the AGS required that the system be able to guide an Abort to the America during any phase of the Challenger’s time as a separate spacecraft. In case of an Abort during Powered Descent or from the lunar surface, the AGS would insert Challenger into an orbit with a pericynthion (perilune or point of closest approach to the Moon) of at least 30,000 feet in order to clear any possible lunar terrain. The design, of course, also required that such a rendezvous be carried out within the fuel available to the Ascent and RCS propulsion systems.[35]

From the beginning of my training as a Lunar Module Pilot, I had tried to find a way to make the AGS a better guidance system, and giving it a better altitude reference prior to landing was the only thing that the AGS engineers and I could come up with that could be done with the existing software. Improving the AGS performance in case of an Abort supplied my primary justification for the effort; however, the question always existed throughout Apollo as to whether a Commander would go ahead and land using the AGS if the PINGs failed close to the surface. No PINGS ever failed, but I wanted to make sure that Cernan had that option if it seemed warranted, so my AGS team worked out a way of updating the AGS altitude reference once Mission Control agreed that the PINGS/Landing Radar data was good. I wanted to be sure that we had every opportunity to finish off the Apollo Program with a great exploration effort. Would Cernan have landed on the AGS data? Close to touchdown, I think he would have. Prior to that? Who knows?]

Okay, AGS [Activation],” Cernan read. “AGS STATUS [switch] to STANDBY.”

“AGS coming on to STANDBY,” I reported to Mission Control, but before I could make the change, Cernan asked, laughing, “Can you pull that LCG breaker.”

I’m sorry?” Cernan’s request to power down the circulation of cold water through the Liquid Cooled Garment came out of context of activation of the AGS.

I’m starting to freeze. …Oooh, that feels good though, I’ll tell you.”

Back on track, I said, “AGS STATUS to STANDBY,” and centered the switch just to the left of the Data Entry and Display Assembly (DEDA) keyboard in front of me (see Fig. 8.8↑ for the status switch position below the green Velcro pad). STANDBY allowed the AGS electronics to warm up and stabilize for a few minutes. Heater power came through the ASA (Abort Sensor Assembly) circuit breaker, closed prior to Undocking.

“MASTER ALARM and AGS [Caution] LIGHT [ON],” I reported to Fullerton. This expected ALARM was caused by sensing of the intentional low voltage provided to the ASA (Abort Sensor Assembly) in STANDBY; but it also provided an additional test of the Caution and Warning circuit for the AGS because adequate voltage had not yet been supplied to its computer.

[Circuit breaker on Panel 16] STABILIZATION/CONTROL: AEA – CLOSED. AEA [Caution] light’s off,” I reported to Cernan, but meant “AGS”, not AEA (Abort Electronics Assembly). Cernan’s circuit breaker panel had a redundant AEA breaker that would be left OPEN for the AGS Activation sequence so that both power circuits could be validated separately rather than simultaneously.

AGS Warning Light, off?” he asked, meaning “Caution Light”.

It’s off,” I repeated. (Fig. 8.9↑, AGS caution light, top left yellow arrow, 3rd light down in the right group next to the AOT brace bar)



Do you have it (the AGS circuit breaker on Panel 16)?” I shook my head and pointed to his circuit breaker Panel 11. He closed the breaker and said, “And the time was 110:52:00 [Ground Elapsed Time].

Okay; got it (the time),” I replied, recorded it, and then said to Fullerton, “110:52:00 for the time on the AGS [AC BUS B breaker, CLOSED].”

“Roger, Jack.”

AGS STATUS at OPERATE.” The ASA had been warming up since going to STANDBY on this switch about a minute earlier. My switch from STANDBY to OPERATE gave us another expected MASTER ALARM and AGS Caution Light because of this change in circuit configuration.

There it is,” I said, referring to the Caution Light.


It’s RESET,” I replied, turning the O2/H2O QUANTITY MONITOR selection switch full left to its C/W RESET position. For some past reason, probably due to a late request from an earlier crew, this switch was chosen for the general purpose of resetting the Caution and Warning lights as well as separately selecting the O2 and H2O quantity sensors in the two sets of Descent Stage and Ascent Stage tanks.

Fig. 8.26. The O2/H2O Quantity Monitor rotary switch is marked at the lower right of panel 2 by the white arrow. The C/W Reset detent position is a full counterclockwise rotation from its current position in the above photo. The Attitude Monitor switch is to the right of the previous rotary switch and is marked by the near-vertical blue arrow. The up position monitors PNGS; and the down position, AGS. (Base photo NASA/ALSJ/Paul Fjeld).


AGS; 412 Read[out – Plus 1,]” This readout on the DEDA (Data Entry and Display Assembly) indicated that the AGS Self Test had been satisfactory. “Oops,” I said as I barely touched the keys for my first actual entry and got more 0’s than I wanted. “Oh, those [DEDA keys] are sensitive. Laughing, I said, “Plink! One! Okay, [now] I want 000…”

Plus six eights,” Cernan read from the Checklist.

…8, 8, 8, 8, 8, 8…” With this entry, I got an Operator Error Light, as expected, showing that alert function was working.

Fig. 8.27. Keyboard schematic for the DEDA showing the operator error (OPR ERR) light to the left of the data indicator bank. Cf. Fig. 8.8↑ for the position of the DEDA in front of the LMP.

And…1, 2, 3 minus…,” continued Cernan.

“Geno,” interrupted Fullerton, we show Jack’s SUIT ISOLATION valve in SUIT DISCONNECT. Should be in SUIT FLOW. Would you check that for us, please?” I went ahead and set the required 45679 in the DEDA register and waited for Cernan to give me a VERB 16 NOUN 65 entry in the DISKEY so I could synchronize the AGS time with that of the PINGS.

“Yes,” Cernan replied to Fullerton as he reached behind me to change the valve position. “He’s in SUIT FLOW now.” It is not clear when or how this valve ended up in the wrong position as we had not changed it during other tests and setups of the ECS system before and after Undocking. I must have accidentally hit the Actuator Override lever on the switch. Why I had not noticed the absence of oxygen flow to my suit, I don’t know. I clearly had flow during the suit loop regulator checks performed earlier and when we had the helmets on for Undocking.

“Okay. Thank you.”

“I tell you,” Cernan continued, “this LCG sure makes a world of difference [in cooling] up here.”


Okay, Geno, [I need] VERB 16 NOUN 65, and I want to set my [AGS] time.”

As Cernan made the entry, he called Evans, “Hey, America; Challenger.”

“Go ahead, Challenger. How you guys doing””

“Hey, Ron, listen. This ridge you’re coming on over – just stick your hand out the hatch and grab a rock.”

“Looks like it’s pretty low down there.”

“Well, when you’re up here looking at where you are, it even looks lower.”

“I bet,” Evans replied, laughing.

Okay, [AGS] clock is counting. Looks good.” While Cernan was chatting with Evans, I had loaded the 377 Address in the DEDA and synchronized the AGS clock with the PINGS by loading 0540.1 minutes, counting from a 110-hour bias so that it could be loaded in the five digit DEDA window.

You happy with your [AGS] clock?”


Cernan went back over the Timeline items related to the AGS clock to verify that we had it right. Then he jumped back and forth between calling out the required AGS entries and looking at America about a mile ahead and somewhat below us.

[Address] 616 plus 0.” This told the AGS not to count seconds of ullage for the Ascent Engine in case of an Abort. “Look at him down there, will you.”

Beautiful,” I replied with a chuckle as America made a remarkable sight moving against the lunar surface background.

Just give me that [Hasselblad] camera one time.”

You might get him over the landing site, if you’re careful,” I suggested, leading to obtaining some of my favorite images from Apollo 17.

I think f/11 against that surface, huh?”

Yes. Well, [we’re] getting close to the landing site. …f/8 or f/11…” The shadows due to the low sun angle near the landing site made the surface dark enough that an f/8 camera aperture seemed about right.

Okay,” I said, getting back to the AGS. “[Address] 224. I got numbers over here, now,” referring to the PAD I had copied from Fullerton, almost two hours earlier. “[224 entry] is 60470. You want to read [the rest of] them?”

Yes, why don’t I read them to you…224 is plus 60470,” Cernan repeated. 224 was the first of six entries needed to update the AGS knowledge of the orbital parameters for which it should target during an abort, based on GUIDO’s current prediction of America’s orbit when we would start our descent into Taurus-Littrow. 224 specifically, told the AGS computer that, in the event of an Abort, what the desired semi-major axis of the orbital insertion ellipse should be. As Cernan read the other entries from the PAD, I carefully entered them in the DEDA keyboard, verifying each before hitting ENTER.

That’s ENTERED; [and] we got a plus [on that].”

I can’t see a plus [or minus from here]…Okay…225 is plus 29364.”

29364 ENTERED.” Technically, Address 225 gave one-half of the lower-limit of the orbital insertion apolune radius, in hundreds of feet, but it basically set the minimum insertion altitude necessary to avoid the highest lunar mountains.

226 is plus 60386.”

60386 ENTERED.” This Address provided the retarget value for a term in the AGS alpha-L calculation.

305 is plus 00594.”



ENTERED.” 305 gave the limit on the retarget phase angle in 0.01 degrees, or 5.94 degrees.

662 is minus 32772.”

32772 minus…[ENTERED]” In the case of an Abort, this number set the length of time that the AGS would hold attitude before beginning to maneuver to the attitude necessary for orbital insertion. The entry gave the time for attitude in increments of 40 micro-seconds or about 1.3 seconds.

73 is minus…”

[You mean] 673?”

[Yes. Minus] 54404.”

[Minus] 54404. [ENTERED]” Address 673 related back to Address 305 that contained the threshold angle for orbit insertion retargeting. Address 673 provided the retargeted value as calculated by Mission Control for a constant (4K10) in the linear mathematical expression for orbit insertion.

That’s affirm. You want to read those out [again]?”

Yes, I do…” and I proceeded to call up each of the previous Addresses while Cernan compared the entries with the PAD values, and I indicated where the values were plus or minus.

Okay,” I said, after we verified the six entries from the PAD and went on with the Timeline items that needed checking but no new entries. “[Now with] 574, you want a plus. …It’s a plus.” The AGS knew, correctly, that Challenger’s Descent Stage remained attached (Not Staged Flag set.).

604, read.”


Okay. Plus is Not On [the Lunar] Surface. That’s good. …612, read. Plus zero is nominal.”

Zeros.” AGS had the ability to tell if we had aborted on or off the Descent Stage (Staging Sequence Counter at zero).

Look at that! Wow!,” Cernan looked out the window, again. “Okay, 232, read.”

Fullerton interrupted, again, with, “Challenger, Houston. I have a new AGS K-Factor for you.”

“Stand by a second,” I requested of Fullerton in order to finish getting the AGS ready. “[00600] That’s good; 232 [is] okay…” This gave a Targeted Insertion Altitude of 60,000 feet.

233, read. [Should be] Plus 00250,” Cernan continued.

That’s got it.” I said. 233 told us that the AGS would keep us going straight up (Vertical Pitch Steering) only to an altitude threshold of 25,000 feet and then would pitch as needed to reach the insertion orbit required for Rendezvous.

464, read.”

Plus 00500.” This number meant we had a 50.0 feet per second Altitude Rate Threshold for the Vertical Pitch Steering Threshold before the AGS could adjust that rate as necessary to reach an insertion orbit.

That’s good. 465, read. [Should be] Plus 00195.” The AGS Targeted Radial Rate at Insertion would have a minimum limit of 19.5 feet per second.

That’s good. 623 read. [Should be] Plus all balls.”

That’s all zeros.” All zeros indicated that AGS guidance would keep Challenger’s z-body axis (Ascent Engine thrust axis) parallel to America’s orbit plane during an Abort, minimizing any out of plane error at insertion.

514?” I asked. The outdoor sights had distracted Cernan, again.

514,” he responded.

Minus 60[000],” I read and Cernan nodded.

515, [should be] minus 44223,” he continued.

That’s good.”


Plus all balls, [that is,] plus all zeros.” Addresses 515, 515 and 516 provided the AGS with the components it needed to implement yaw steering if needed to drive to America’s orbital plane and end up with zero out-of-plane velocity.

“Go with the K factor,” I finally got back to Fullerton’s earlier request.

“Okay, its 109:59:59.94. Over.”

“109:59:59.94,” I read back. This Ground Elapsed Time would be time zero or what was termed the “K-Factor” for the AGS. The AGS clock could run about 72 hours before a new K-Factor would be required.

While I waited to continue getting the AGS ready for Powered Descent, Cernan watched and photographed America out ahead and below us, referring to the lunar mountains as “Pretty darn close!” They would get closer.

“Gordo, this is spectacular. It is absolutely spectacular, looking at the Command Module, America, down there coming across the surface. We’re just tracking him at about a 30-degree dive angle,” observed Cernan, calling on his combat pilot training for the “dive angle” description (Fig. 8.28).

“Sounds great,” said Fullerton.

Evans responded with, “Okay, Challenger – America [here]. Good luck on your PDI burn down there. I’m going to track your landmark for you.”

[Lunar landmark tracking using the CSM 60× star-sighting telescope was a technique designed to minimize the effect of the irregular lunar gravity field on landing accuracy. It began to be developed on Apollo 8, the first human mission to the Moon in 1968. At his request, I had helped Jim Lovell refine the technique that he in turn verified in flight. Now, Evans’ manual sextant tracking of specific small craters, and marking on them, near the landing site would be used to improve significantly the Mission Control’s data on the location of the Taurus-Littrow landing site relative to his spacecraft’s orbit. Mission Planning and Analysis Division previously had determined the position of these craters relative to the center of mass of the Moon, using photographs and orbital tracking data from the Apollo 15 mission. By repetitively marking on these craters in America’s P24 Landmark Tracking Program, Evans tied his orbit more closely to the landing site and the center of mass of the Moon. These data would be processed by Mission Control, adjusted for the separation of the two spacecraft, and incorporated in Challenger’s state vector just prior to Powered Descent Initiation early in the next orbit, an orbit later than on previous Apollo missions. This process had made it possible to shrink the errors associated with all trajectory variables so that Taurus-Littrow became an acceptable landing site for the mission. ]

Okay, Babe,” Cernan said to Evans. “Have a good time and go get that landmark. Don’t forget: No TEIs! See you in about three days.” Cernan’s continued request for “no TEIs” was all in good humor. Actually, Ron always needed to have the PAD data needed for a no-communications “TransEarth Injection” burn in case of a landing abort and rendezvous without assistance from Mission Control.

Will do.”

VERB 47,” I requested of Cernan, trying to get back to the AGS Activation.

Okay, coming at you.” VERB 47 would allow the PINGS to initialize the AGS state vector.

Interrupting this process to get the Hasselbald ready, I said, “I’m going to try to get him [Evans]; if we’re still in attitude.

Fig. 8.28. Cernan captures Ron Evans at a 30° “dive angle” in America as we both approached the coastline of western Mare Crisium. He is moving faster because his trajectory is lower than ours. The bright, oblong crater Tisserand K whose western rim looks like a snow-capped Alp, slopes down and intersects the window frame. It is roughly 24 km × 12 km in size. The line-of-sight distance from us to the white western peak of the west rim is ~62 km. Our elliptical orbit has brought us down to an altitude of 31 km. On the horizon directly ahead of that peak, the bright area is on the southern wall of Macrobius crater, 106 km distant. We will pass to the south of it on our way to Taurus-Littrow valley, 555 km ahead and over the horizon from us. (NASA photo AS17-147-22463).

Handing the camera to Cernan, he urged the Hasselblad to give him a good photo. “Come on, Babe!” (Fig. 8.28). Back to the AGS, Cernan followed the VERB 47 with a VERB 25 and loaded in the AGS K Factor (time bias) I gave him.

109:59:59.94,” he repeated.

That’s good,” I confirmed. “PROCEED.”

And you want the 4….”

Wait a minute. …[Do we want] high bit rate [for the PINGS downlink to the AGS]?” I checked to make sure that the position of the TELEMETRY PCM switch was correct.

I just PROCEEDed,” Cernan said after I gave him a thumb’s up.

That’s good. So did I,” meaning I entered 414+1 in the DEDA to enable the Initialization from the PINGS. After the DISKEY displayed a flashing 50 16, indicating the transfer to the AGS from the PINGS had been completed, I then entered 400+3 to align the AGS gyros to the PINGS platform.

“Geno, Houston,” Fullerton called, “with a couple of items.

“Yes. Go ahead, Gordo.”

“Your perilune seems to be…”

Look at that! Look at where he’s (Evans) coming over,” I exclaimed before Fullerton could finish. (The 1:46 min LM DAC video of this approach to Taurus-Littrow can be viewed here.[36] Evans in America passes over the entrance to the valley at ~35 sec.)

“Hey we got the landing site [in view], Gordo!,” Cernan said, reacting to my heads-up comment.

“I got it too!,” Evans broke in.

“Hey, Gordo, we got the landing site [out the window]. We’re coming right over the front [east end] of it. Standby a minute. You can see the slide. I think you can see the Great Cross.” I do not recall what pattern of craters Cernan referred to as “the Great Cross.” It must have been a pattern he personally kept in mind without using it frequently during simulations.

“The light mantle.” I laughingly corrected Cernan on his calling this feature “the slide”, as it being a slide or avalanche were two of the hypotheses we were supposed to evaluate.

“[It’s] beautiful,” came the word from Evans.

“We’ll get a picture of America coming right across it,” Cernan added. Cernan got several great pictures (AS17-147-22464, -65, -66, 67) of America over Taurus-Littrow just as Evans performed his landmark tracking routine. (see Fig. 8.29).

Fig. 8.29. View of the Command and Service Module America crossing Bear Mt. and heading towards the South Massif just south of the valley of Taurus-Littrow on Apollo 17’s orbit prior to Challenger’s landing. Cernan took the photograph through his forward looking window. The LM altitude is 25 km. (NASA Photo AS17-147-22465).


“Super targeting!,” I said, complementing the Mission Control team.

“Gosh,” continued Cernan, “we’ve got Family Mountain. We’ve got, of course, the Massifs. We can see the [Jefferson-Lincoln] Scarp; we can see the light mantel; I’ve got the Great Cross, Camelot [and] Sherlock [Craters].”

Fig. 8.30. An enlargement from Fig. 8.29 showing the CSM America in better detail. The yellow glow on the rear of the spacecraft is from the tracking light. The white lines on the valley floor mark the pattern of craters Cernan may have been referring to as the “Great Cross”. Cf. Fig. 8.29.

Fig. 8.31. An anaglyph made from two of Cernan’s valley floor photos with the CSM positioned just above the crest of the South Massif. The “Great Cross” on the valley floor is also evident. (From Fig. 1, p. 115 of the Editor’s 3D book, derived from NASA photos AS17-147-22466, -67).

“Believe it or not, Houston, they’re all there,” I said, jokingly. More seriously, I went on, “I see possible structure [layering?] of the upper part of the South Massif, a little bit east of Station 2 [location]. It’s sub-horizontal, dipping (plunging) to the southeast.”

“Houston, I can even see Poppy right where we’re going to set this baby down. …Matter of fact, I can see Rudolph. I can see the triangle – Rudolph, Frosty and Punk. Man, Gordo, this is absolutely spectacular! Man, Gordo, this is absolutely spectacular!

“Sure sounds like it.”

“We can watch Ron track right on through the landmarks. I don’t know what kind of results he got, but he sure had a nice smooth track from here.” Newtonian physics strikes again.

“Beautiful results,” said Evans. This news meant that our guidance targeting for landing would be as good as it could get.

Let’s go to work, Geno.” We were running about ten minutes behind in our preparations for Powered Descent on the next orbit.

Let’s go, Babe!” Seeing the landing site may have brought Cernan’s focus back to the business at hand.

Okay. You [already] got your 400 plus 3,” I said as I reminded Cernan that the AGS had aligned its strapped down gyros with the more stable gyros of the PINGS.

“Gordo,” Cernan interrupted, again, “you can go ahead and update us with those words [you mentioned, previously].”

“Okay,” Fullerton responded. “Your perilune is shifting west.”

[At the start of Powered Descent, perilune or the low point in our elliptical orbit, was intended to be over the landing site in order to save Descent Engine propellant. This shift to the west resulted from the then unpredictable, small perturbations in the Moon’s gravity field caused by variations in lunar mass along our orbital path. The 2011 GRAIL mission has since greatly improved our knowledge of this field. ]

“PDI will be a little higher than nominal: 10.7 [nautical] miles or 65,000 feet – should be no problem. And, [secondly], from the time you first came around [on this orbit] until we had a solid lockup on the Steerable [S-Band Antenna] on this acquisition was about three minutes. We’re going to try to speed that up some on the next time around. We’d like you to just keep trying the Steerable until we come to you and say ‘stop trying’. Over.”

To which I responded, “Okay, Gordy, understand that, …and apparently this time had I waited a little longer, it (signal strength) would have dropped to zero and then come up [on its own], because that’s what happened when I finally got you. I’ll give it more time [to lock-up] next time.”

“Okay. …And, Jack, I’ve got lots of PADs for you whenever you’re ready.”

Look at those ridges,” I said, glancing out the window as we flew over the dark gray mare of the southern part of the Serenitatis Basin. (Ridges that Ron is crossing at 1:30 in the above linked video.)  …Damn, if those mare ridges aren’t extrusive, I’ll eat my hat.” The ridges have been studied extensively since, and most investigators believe that they are pressure ridges and thrust faults that have formed due to the slow contraction of the Moon as it has slowly cooled[37] since the last major mare basalt eruptions about three billion years ago. So in a sense, the ridges are “extrusive” except the process is not related to lava, but rather to thrust faults that break the surface.

You want to set your [radar data]. …Check your VERB 83?” Cernan inquired. VERB 83 in the PINGS displayed the Rendezvous Radar Range and Range Rate, and I used these to verify the comparable 317 and 440 Addresses, respectively in the AGS. Following this check, Cernan set the ORDEAL (Orbital Rate Display-Earth and Lunar) function by closing the AC BUS B – ORDEAL and FLIGHT DISPLAYS circuit breakers on Panel 11 and then, on a panel just below Panel 11, putting his FDAI (8-ball) switches in ORBITAL RATE and LUNAR. Calling up a VERB 82 displayed Challenger’s current orbital parameters. Being in ORB Rate for the remainder of our preparations for Powered Descent would keep us in a constant orientation relative to the lunar surface until it became time to maneuver again.

Fig. 8.32. (Lower): The ten AC BUS B circuit breakers on the aft, upper row of panel 11 outlined by the white oval. (Upper): An enlargement of the area marked in the lower photo to show the switches more clearly. The ORDEAL circuit breaker is indicated by the white arrow. The AGC and AOT Lamp circuit breakers are to the immediate right, respectively. (Base photo NASA/ALSJ/Paul Fjeld).

AGS Control and Rendezvous Radar Checks

I’ll make the AGS Control Checks while you get the PADs,” Cernan said. We got to get a P52 [alignment] here pretty soon. Okay. …We’re a little behind.”

All right. …Okay, Gordy, go with the PADs.” The information Fullerton was going to provide, as with many PADs, related to various contingencies that might result from a loss of communications (S-band and VHF), a significant and urgent hardware failure, or other urgent event that would prevent going forward with the normal Flight Plan and require us to take timely action without input from Mission Control.

“Okay. The first one is a P76 for the CSM Circ[ularization burn].” Evans, now in a 10×60 nm orbit, would “circularize” America’s orbit to about 70 by 55 nm above the lunar surface with a three second SPS burn behind the Moon prior to our second Descent Orbit Insertion (DOI-2) burn half an orbit before Powered Descent Initiation. We would use a P76 State Vector Update as the basis for a rendezvous with America in this new orbit in case of an Abort before any further state vector refinements could be made.


“NOUN 33 (Time of Ignition) is 111:57:30.09; NOUN 84 (America’s predicted x, y and z axis velocities in feet per second): plus 0070.5, plus five zeros, and minus 0000.5. Go ahead [with the read-back.]”

“111:57:30.09; plus 0070.5; plus five zeros; and minus 0000.5.”

“Good read-back. Next one I have is the NO PDI plus 12 Abort (using the Descent Engine), item Echo [on the PAD sheet].”

“Go ahead.”

“Echo (Time of Ignition) is 113:02:00.00; Foxtrot (America’s predicted x, y and z axis velocities): plus 0103.4, plus five zeros, minus 0050.0 fps; NOUN 42 (pre-burn apolune and perilune and required Delta-V): 0142.0 nm, plus 0005.4 nm, 0114.9 fps; burn-time is 0:48 sec; 000º, 272º (roll and pitch attitudes); 373 (AGS Time of Ignition) is 0182.0 min; AGS [x, y and z axes] DELTA-Vs: plus 0103.7, plus five zeros, minus 0049.3 fps; Golf (early PDI Abort time): 113:57:00.00; Hotel (late PDI Abort time): 115:36:45.00; and the NO DOI-2 DELTA-Vx, 0096.6 fps. Two remarks: Throttle Profile is 10 percent for 26 seconds, 40 percent for the rest of the burn. Over.

I then gave Fullerton the read-back.

Meanwhile, Cernan had performed an AGS Control Check by setting the MODE CONTROL for the AGS to ATTITUDE HOLD and then putting GUIDANCE CONTROL to AGS and maneuvering with his hand controller to 0º roll, 315º pitch, and 0º yaw on his eight ball. He then set up for a Rendezvous Radar Checkout that would be coordinated with Evans. GUIDANCE CONTROL went back to PNGS and he closed the RENDEZVOUS RADAR and the PINGS/RENDEZVOUS RADAR circuit breakers on his panel.

Challenger; America,” Evans called. “You want to try VHF RANGING and RENDEZVOUS RADAR comparison?”

“Just a second,” Cernan answered. “Give me a transponder, and we’ll start with the [Rendezvous] Radar. Jack’s tied up right now.”

“Okay. Transponder’s coming on now”

Gordo,” Cernan said, meaning “Jack”. We need VOICE [and] RANGE, when you can get it.”

Then, Fullerton broke in with, “That’s a good read-back. Item India 112:49:52.35…”

A suddenly irritated Commander asked, “Any way he can wait?” “Say, Gordo, Gordo, Gordo. Hey, Gordo; stand by! We want to finish the Radar/VHF [comparison] test; and when I go to P52 [alignment], you can finish the PADs.” Fullerton should have realized that these tests were underway, but apparently he missed the transmissions between Cernan and Evans.


Okay, We need VOICE/RANGE.” I repeated Cernan’s Timeline request and reached to my right and moved the VHF A TRANSMITTER switch to VOICE/RANGE. After checking the Radar temperature was within the 10-75 degrees limit, Cernan put the RATE/ERROR MONITOR switch for the eight ball error needles to RENDEZVOUS RADAR, the Radar’s rotary switch to SLEW and manually moved the Radar Antenna until he had a lock-on America’s transponder. With a lock-on, he put the rotary switch to LGC (Lunar Module Guidance Computer) that lets the PINGS maintain lock. He set the Tape meter switch to RANGE/RANGE RATE and, through a VERB 63 entry in the DISKEY, started the Rendezvous Radar through its self-test routine. A PROCEED caused the NO TRACK LIGHT to go OUT and another PROCEED brought up NOUN 78’s readout of RANGE and RANGE RATE.

Fig. 8.33. The switches for the rendezvous radar settings. The radar temperature monitor is marked by the red double arrow right of middle in panel 3— the rotary switch below selects the radars in the left detents or the RCS quads in the right detents (the reaction control tape meters are the three at the top of panel 2, temperature, pressure, and quantity remaining marked by the orange arrow below the AOT brace bar). The rectangular tape meter above the red arrows shows the temperature readings. The Rate/Error monitor switches are indicated by the yellow arrows left of the CDR and right of the LMP 8-balls. Toggle up selects the rendezvous radar; toggle down, the landing radar/computer. The rendezvous radar controls are towards the left of panel 3. The rotary switch marked by the blue arrow can select between auto, slew, and LGC. The toggle switches denoted by the pale green double arrow to the left control the manual motion of the antenna—the top one sets the slew rate. The lower one is a 4-position switch for up-down, left-right. The white arrow points to the radar signal strength meter. To its left, the dark green arrow points to the engine gimble enable switch. Finally, the light blue arrow marks the toggle next to the tape meter above the Abort Stage button in the middle of the photo. It sets the range/range-rate (up) or alt/alt-rate (down). (Base photo NASA/ALSJ/Paul Fjeld).

“We’re in VHF RANGING, and I’ve got you on Radar, Ron. We’ll be quiet for a second and see if you can get a lock-on.”

Seconds later, Evans exclaimed, “Ah-ha, it worked!”

“We got your tone, Ron!,” I called, when the VHF ranging tone indicating a lock-on came through our headsets. “We got your tone.”

“Okay. 0.50 or 0.49 [nautical] miles.”

There you go!” This was the same as we were reading IN NOUN 78 and from the Radar on the Tape meter. We did not have a VHF RANGE readout in the Challenger.

“Okay, Gordo. The VHF Ranging and Radar check out very well [with Ron’s range number],” Cernan reported.

“Okay, sounds good,” responded Fullerton. “Tell me when you’re ready for item India, again.”

Okay. Let’s wait a minute.”, I said. Cernan first terminated the PINGS self-test with a VERB 34 entry, and I put VHF A TRANSMITTER back to VOICE. The Rendezvous Radar’s Coupling Data Unit was aligned to its stowed position (180º pitch and 283º yaw) with a VERB 41, NOUN 72 entry.

“We cut you off [VHF], Ron. …Go ahead, Gordy.” This became about the last substantive interaction we would have with Evans until we returned from the lunar surface. Challenger had become an operating, independent spacecraft.

“India (second planned Abort after landing – T2) is 112:49:52.35; 11:01 [burn time], plus 0002.2; attitude is 002, 108, 290; plus 56900; Juliet, 115:36:45.00; Kilo, 117:35:45.00. Go ahead.”

Following my read-back, Fullerton continued, “That’s a good read-back. Lima is 113:14:24.91; Mary, 119:34:30.00; and November is 114:57:19.09. And your T-2 at PDI: T-2 will be at PDI plus 24:33.”

With that read-back complete, Cernan said, “Okay, Jack, I’m ready on the P52.”

“One thing left, Jack,” Fullerton broke in, “is the SHe (Supercritical Helium) pressures on the PDI page.”

“Go ahead.”

“At [PDI] T-Ignition, the pressure will be 1310; plus 1 minute, 1410; 2 minutes, 1400; 3 minutes, 1310; and 4 minutes, 1230. Over.” This pressure profile related to the warm up followed by drawdown of the Super Critical Helium in the early minutes of the PDI DPS burn.

“Okay, I got those. Thank you.”

Inertial Measuring Unit Fine Alignment

As I finished copying and reading back the PADs, Cernan prepared for the second round of a P52 fine alignment of the guidance platform. He set the DAP in its Minimum Impulse Mode (VERB 76), called up P52 on the DISKEY, and closed the AOT LAMP circuit breaker (Fig. 8.32↑; upper; the AGS and AOT Lamp circuit breakers are just to the right of the ORDEAL switch). As indicated by the Checklist, he selected Option 3 in P52, the REFSMMAT Option. The REFSMMAT option (the alignment would be referenced to the inertial position of the landing site) meant the PINGS would maneuver Challenger so that two navigation stars were visible in the AOT in its straight ahead detent. Cernan would only Mark the stars as they crossed the Cursor X and Y axes but not the Spiral. The PINGS would automatically record the Marks so I did not need to enter numbers from the AOT counter.

We got the Earth in the top of this thing (AOT),” Cernan commented. “That was a Y [reticle Mark], Jack, do you concur?”

Yes, it was a Y.”

Another Y?”

Yes, sir.”

This the third Y?”

Right. [Checklist calls for] four Ys.”

Okay…Sirius, Castor, Pollux and the Earth,” Cernan mused as he scanned his AOT field of view.

I’m on Procyon [in the computer],” I noted, confused by Cernan’s mention of other stars and the Earth. The PINGS had picked Procyon (216) and Aldebaran (211) as also called for in the Timeline Book.

Try not to push (hit) me if you can.” Cernan was looking through the AOT eyepiece near the top of the cabin. As I worked the DISKEY with my left hand, I was unknowingly bumping his leg and disturbing his eye position. “It’s an X [reticle Mark]?”

That’s right.”


I had turned my Intercom switch off when talking with Fullerton and Cernan was having trouble hearing me without it. I turned it on and repeated, “That’s right. …The Intercom was off to copy those PADs.” Then I hit his leg again.

Every time you do that…”


If you could help [not doing] it. …This thing is really sensitive. …I didn’t like that [Mark]. …I should have rejected. …That’s it (the Mark). …Okay.”

[Is that] Three [Marks]?”

Four. …Okay, I like those. I can’t mark them any better. Okay, next star is what?”

Stand by,” I said, turning to the Checklist. “Star is Aldebaran. …[number] 211.”

Okay, that’s what we got [on the DISKEY]. …289. That should be easy to follow. Would you believe ‘Orion’? Would you believe our footpad or something up there. …[Maybe the] Radar. Can’t be our footpad.”

See the Command Module in Earthlight?”

Yes, I saw it a little while ago. …That’s Aldebaran, all right.”

Okay,” I acknowledged. “Let’s try X [reticle] first.”

Go ahead. …Certain places in this telescope you can see double line. …Okay, that was a good one.”

Challenger; America,” Evans called. “How do you read on SIMPLEX A?” He was doing a communications check before his circularization burn.

You’re loud and clear,” I answered.

Okay, got you loud and clear, too.”

To Cernan, I said, Two on X.…Didn’t like it?”

Just like the simulator – you can move your eye position and the star moves. Isn’t that beautiful? Four Ys.”

You got four Xs.”

Boy, I tell you, this is the hardest alignment in the world. Ron ought to be thankful [for his sextant setup].  …One.  …Got two Y.  …Three Ys.”

“Okay, PROCEED there,”

Evans broke in. “Challenger and Houston, I’m maneuvering to circ[ularization] burn attitude.

“Roger, America. Have a good burn,” I acknowledged.

“Okay, sure will.”

“You look just as pretty in Earthlight as you do in Sunlight.”

“Oh, great!”

Well, my eyes aren’t any better than that, Jack,” Cernan said as he wrapped up the sightings through the AOT and I called up the NOUN 05 in P52 to record the very small angle differences between the old alignment and that which would result from Cernan’s new star sightings. Then I PROCEEDED and called up the Torquing Angles with a NOUN 93 which would give Mission Control a look and me a chance to copy them before we realigned the IMU (Inertial Measurement Unit).

“Looks like a good job,” commented Fullerton after word from Presley or Ferguson at the GUIDO console.

“Yes, but it’s not an easy one, Gordo,” Cernan complained.

Once again, Evans called. “Hey, Challenger, America.”

“Go ahead.”

“Okay, Jack, can you go to RECEIVE ONLY on your VHF, there? I’ve got all these PADs to pick up now. I’ll call you when I’m all through.” Evan’s must have had to listen to all our conversation during the P52 activities.

“Okay, RECEIVE ONLY.” Then, to Fullerton, “We got your GO [for realigning the gyros]?”

“That’s affirmative – torque them,” Fullerton replied after the usual thumbs-up from GUIDO.

In response, Cernan said to me, “Ready?”

Yes.” Cernan hit PROCEED to torque the gyro gimbals and I recorded the Ground Elapse Time for future reference.

Yes, I guess you did copy them [down].” Cernan declared.

Yes, I got them. …Now we want to do some other things with our [time]. …Where are we [in the Checklist]?

Crew Optical Alignment System (COAS) Calibration

So we PRO and ENTER,” Cernan said, reading the first step in the COAS Calibration procedure. Still in P52, Cernan PROCEEDed to a NOUN 70 to enter zero plus a star code to tell the PINGS we were beginning a COAS Calibration. During the second major phase of Powered Descent, the PINGS will display reticle x and y coordinates for a point in the COAS that I will give to Cernan so that he has a visual reference as to where we are going to land if we do nothing to redirect the PINGS.

[The COAS mounts at eye level in a precise structural position in the right frame of Challenger’s left hand window (Fig. 8.11↑). This optical aid would be critical as a backup means of aligning the guidance system if the AOT failed. The COAS consists of a closed optical tube with a projected perpendicular reticle that was graduated by four plus (+) marks in all four directions. Mounted in the Commander’s window, it would be bore-sighted along Challenger’s +z-axis. (Mounted in the overhead window and bore-sighted along the +x-axis, the COAS also could be used as an optical docking aid in the event that the Lunar Module had to be the active vehicle after rendezvous with the CSM.)]

I had ENTERED 001 in the DISKEY, but Cernan asked, “I want [00]001, huh?”

Yes [I mean, no]. …Okay, I got [an extra] zero in there [and missed one]…” I corrected this to 00011 in NOUN 70, indicating to the computer that we were calibrating the COAS as a Landing Point Designator (LPD) and would use the star Aldebaran (still shown directly in front of us). I then PROCEEDed on this display to get the NOUN 87 readout of Azimuth (±y) and Elevation (±x) in the COAS grid where he should see Aldebaran.

Okay, [the PINGS says it is at plus] 3 [and plus] 3. Let’s go see where that puts it [in the COAS]. …Oh shit, you know what I did, smart guy [that I am]. I got ahead of the game a little while ago so I took this (COAS) out [of its front window holder].” Why he would have done this earlier is not clear, unless it was to avoid it interfering with photography.

Who’s this? Who’s this? Who’s this?” I said, giving the Commander a hard time after I had just screwed up the first NOUN 70 entry.

Challenger,” Fullerton called, “we need AFT OMNI [for S-Band] and select the Steerable [Antenna] to SLEW. …And LOW bit rate [on the S-Band PCM].”

Half a degree up [positive elevation] and zero left and right [in azimuth],” Cernan updated NOUN 87 after finding the COAS in one of his stowage bags and mounting it in his window.

Fullerton tried again. TELEMU had changed its mind. “Challenger, select FORWARD OMNI, please.”

“Say again,” I requested, as Cernan looked through the COAS grid and said “Up…elevation half a degree up and zero on azimuth. …Okay.” He found Aldebaran right where the PINGS said it would be. Clearly, the computer knew exactly where the COAS was pointed.

Meanwhile, I had recalled what Fullerton had asked for and reconfigured the S-Band switches as well as putting the UPDATA LINK switch to DATA. This enabled GUIDO to uplink new State Vectors into the PINGS for both America and Challenger, update our E-MEMORY, and provide a first cut at Descent Targeting. The latter would be revised later, using Evans’ landmark tracking data that would be incorporated just before Powered Descent Initiation.

Where’s our DAP?” Cernan asked himself as he PROCEEDed out of P52 and put the computer into idle (P00). The DAP had been in its MINIMUM IMPULSE MODE for the star sightings and now he reset it to RATE COMMAND/ATTITUDE HOLD MODE with a VERB 77 entry in the DISKEY.

You [put the AOT in] CL (centerline detent)?” Cernan asked, as called for in the Timeline.

No.” But then I did so.

“Okay, Gordo. The COAS align is good, and the DAP is reset,” Cernan reported.

Turn your AOT lamp out [with the circuit breaker]?” I asked, before turning the page of the Timeline (Fig. 8.32↑, 2nd switch right of the ORDEAL circuit breaker).


“Okay,” came back Fullerton after Flight Director Griffin had polled the consoles, “and like the rest of the spacecraft, the platform’s beautiful. There’s no drift compensation or PIPA bias update. Over.”

“Fantastic!,” I replied. PIPA stood for Pulse Integrating Pendulous Accelerometer. The absence of any observed drift in these high precision accelerometers meant that they were working extremely well.

“Beautiful!,” added Cernan. “No PIPA bias or drift compensation. Boy, I hope it stays that way.

“This doesn’t sound like a Sim[ulation],” I joked. SIMSUP loved to put in some drift or an actual failure of a PIPA during our Mission Simulations.

What do you want, [again] – AOT?” Cernan asked. “You [take care of the AOT] Centerline.”

“Yes, [AOT circuit breaker] OPEN. …Yes, I’m all set [with the AOT Centerline.]”

“Okay, Challenger, America,” Evans came on the loop. “I’m through with all the PADs now.” He had a lot of contingencies with which to deal and only himself to keep it all straight.

“Give you one update,” said Fullerton to us. “You can write it in the timeline, page 8, the T-1 [post-landing Abort] time is PDI plus 17:00. Over.”

“17:00,” confirmed Cernan. “T-1 is PDI plus 17:00. We got it.” I immediately changed the Timeline Book number from 17:16 to 17:00. Sixteen seconds later in an Abort from the lunar surface would mean significantly smaller Ascent propellant margins.

Now where are we [in the Timeline]?” Cernan asked, rhetorically. Did we do all this,” looking at page 3. “Okay. That’s good we got all that. How are we on time? Little behind – let’s press.”

“Okay, Houston – you’ve got P00 and Data,” I told Fullerton.


That [Event] clock counting down to anything?” Cernan asked.

Yes, [to] DOI-2.”

Okay.” DOI-2 would be a short RCS burn on the far-side of the Moon, directly opposite the Taurus Littrow landing site. The purpose would be to lower the altitude at which Powered Descent would start and thus save propellant needed by the Descent Engine for landing.

AGS Calibration

Now we got a maneuver to the AGS Calibration [attitude],” Cernan noted in the Timeline Book.

No, wait a minute,” I said, concerned about the fact that Mission Control uplink was still in progress and we might lose S-Band lock.

I guess, I can’t do that while [data’s coming in].

…Yes, Go ahead,” I finally said as the uplink was complete.

ROLL of 24. I am about there. PITCH is 77. I got to go up a ways. And YAW 39…Guess I can’t maneuver while he…Are you in High Gain?”

No, [we’re] using the OMNI.”

“Gordo, can I start maneuvering to the AGS Cal [attitude] while you’re getting those uplinks ready?”

“Okay,” Fullerton replied. “[But] we’d like the Steerable back again. Try PITCH of minus 25 and YAW of minus 72.”

Minus 30 and 72,” Cernan replied, apparently only half listening or possibly reading the numbers that a NOUN 51 gave for positioning the Steerable. Anyway, I moved the Steerable S-Band Antenna close to this position.

“You got the Steerable,” I told Fullerton when I saw the signal strength was good. (The S-Band signal strength meter is the black disk with white numbered scale marked by the yellow arrow in Fig. 8.33a below).

Fig. 8.33a. The VHF and S-Band communication antenna controls to the aft of panel 12. The yellow arrow marks the signal strength meter. Note also the attachment links for the LMP’s cable restraints marked by the white arrow. (Base photo NASA/ ALSJ/Paul Fjeld).

“Okay, we need HIGH Bit Rate,” requested Fullerton, and I moved the PCM switch to HI.

And I can see the Earth,” Cernan commented, “so my maneuver is not going to hurt them.  …I’ll start over.”

“If we start on the uplinks now,” Fullerton, suggested, “we’ll get that in before we go to the AGS Cal attitude. Over.”

“Okay, Gordo, [but] I’ve got the Earth [in view], and the direction I have to maneuver is nothing but good for the High Gain, so I’ll start over slowly.” With the Steerable Antenna in TRACK MODE in AUTO, it should hold lock on the S-Band beam.


A few minutes later, Cernan said, “Boy, I tell you, those P52s are hard. …In this thing, you can either attenuate the star or you can attenuate part of the line (reticle) or make the line double, and it’s really [hard]. I remember it that way in the past (Apollo 10). …You know while we’re doing that, you could [stabilize me]. …Well, we can do that on the [lunar] surface.”

Unsure what he was talking about me doing, I mumbled, “Well, I mean…”

Unless you can…move this [hose] over.”


Forget it,” Cernan finally said.

Yes, Let’s [get there first].”

It won’t bother me. We got to land first, anyway. …Jack, I think I discovered something.”


There’s no light in there [the DEDA keyboard]. I don’t know if there was ever supposed to be, but there isn’t. …No, you may have a hard time seeing it.”

I think there will be enough light in the cockpit because it’ll be daylight,” I observed. We also had the floodlights as well as some lights on movable clamps. At the extreme, we both had small flashlights.

We got all the PADs?” Cernan asked while we waited to get to the right attitude for AGS Calibration.

Yes. I updated times in there (the Timeline Book), too.”

That’s good.”

Challenger, Houston. It’s your computer. [Put] UPDATA LINK – OFF.”


“Hey, Challenger, America. Are you still with me?”

“Still with you,” I answered.

“Okay, I got something like ‘yes’”.

“Something like what? Say again, Ron.”

“I just want to make sure on the Voice Check if we still have the VHF problem.”

“I’ll have to give you another one (voice check) here in a minute.”

I was occupied with preparing for the AGS Calibration, first with a PINGS’ VERB 47 that set up its computer to initialize the AGS and then loading a 414 +10000 in the DEDA to enable Navigation Initialization via the PINGS Downlink. A 400 +30000 followed to align the AGS gyros with the PINGS IMU. A VERB 83 in the PINGS displayed Rendezvous Parameters of Range and Range Rate on the DISKEY. Then I compared the PINGS Range to America with that shown by a 317 DEDA entry and the PINGS Range Rate with that of a 440 entry.

Going to have to [hurry up],” Cernan said.

[VHF ANTENNA goes to] AFT, [and the VHF B TRANSMITTER goes to] DATA,” I said as I continued through the Timeline items.


I’ll check them (Range and Range Rate) when we have [AGS CAL] attitude, but they shouldn’t change. …Okay, [Ron], How do you read?”

“Okay, loud and clear. How me, Jack?”

“You’re loud and clear.”

Now, I recorded the initial, pre-calibration readouts for the AGS x, y and z-axis accelerometer bias component coefficients (540, 541, 542) and the x, y and z axis gyro drift component coefficients (544, 545, 546).

You got all these [items],” I asked Cernan, pointing to setup items in the Timeline that preceded the actual AGS Gyro and Accelerometer Calibration that would come with my DEDA entry of 400 +60000. These included putting PINGS MODE CONTROL in ATTITUDE HOLD, displaying PINGS Attitude Rates on the eight ball error needles with a VERB 60 entry, setting MINIMUM IMPLUSE MODE in the DAP with VERB 76, and, finally, using VERB 16 NOUN 20 to display ICDU (Inertial Coupling Data Unit) gimble angles on the DISKEY.

We are all within limits [on the Attitude Rates], Jack. If I perturbate one [rate], I’ll perturbate them all.” These rates needed to be less than 0.075º per second.

I then entered 400 +60000 to calibrate the AGS to the PINGS. While the calibration took place, we monitored the PINGS display to insure that the ICDU angles stayed within designated limits and then I entered 400 +00000 to freeze the calibration. A repeat of the previous six DEDA entries gave us the accelerometer and gyro calibration coefficients. All numbers fell within the limits given in the Timeline.

During the wait for the AGS calibration, I ran through a quick check of the status of the ECS, RCS, EPS, and APS systems and cycled the Caution and Warning circuit breaker to reset that system.

Okay,” I said, as we completed the AGS Calibration. “You ready to go, then?”

Yes,” Cernan agreed.

Okay; at 30:38 [to DOI-2].”

My suit feels shorter,” Cernan observed.

Like Charlie said, ‘you grew’.”

This water is a lot less airy,” Cernan said as he drank from the water gun, “after I got the first few gulps out.”

Oh, you been drinking on me, huh?” I kidded… “I guess I better fix this,” referring to settings on the camera.

I guess I better change [film] mag[azine]s,” Cernan replied.

Can you look in there (Timeline Book) and find out – Is there anything on cameras?”

Yes. Way back here. We skipped it. Camera setting for cabin. …Oh, for cabin photos. …You take cabin photos during rendezvous. …We don’t want to worry about that.”

Want to do that now? I asked.

It’s too dark.” We had crossed the sunrise terminator some time ago.

Yes. I don’t think we’re going to have time,” I said.

Jack, I don’t see [any camera settings in the Timeline] anywhere.”

I think it was supposed to have been this one (Sequence Camera magazine). But I have only 50 percent left on this one.”

Okay. …I changed mags, so we can always use that other one [for something else], but I don’t know what your settings are. They aren’t in here. Are they supposed to be?”

Yes. They’re there somewhere.” The camera settings in the Timeline came during the AGS control Continuity Check that Cernan had done alone while I was working on activating the AGS. The settings related to Sequence and Hasselblad Camera photography of the landing site during our last closest approach; but we had spent the time looking rather than photographing.

Can you get to the ISA (Interim Stowage Assembly)?” Cernan asked.


I thought I put it [the magazine] in the top pocket.”

No, I think it’s in the bottom. …Yes, give me mag Oscar. Unless that’s the one I had on there (the camera). …No, give me mag EE, …Give me the spare one.”

Which one is that?”


You want to put the other one (Oscar) in your side kit, somewhere? Cernan asked, “because that’s not done (finished). …Where’s that other mag?”

It’s right here; I’ll get it.”

Why don’t you just mark it ‘undocking’ or something,” Cernan suggested.

Yes, I will…”

[I’m] ready when you want those numbers [for the Sequence Camera or DAC].” Cernan had looked ahead in the Timeline for the camera setting for Powered Descent and landing.

Challenger, Houston. You’re GO for DOI-2,” Fullerton reported.

“Thank you, Gordo,” Cernan replied. We’re GO here for DOI-2.”

What are the numbers [for the Sequence camera]?” I asked Cernan.

Okay, f/2.8 at 500 [of a second] and infinity.”

How many frames [per second}? Twelve?”

Wait a minute” …That’s the DAC. Camera…,”

That’s (DAC) what I want. …Yes, twelve frames per second, f/2.8 and infinity, huh?”

Yes, [but] infinity doesn’t seem right, but I guess it is…f/2.8, 1/500th at infinity.”

Okay, I got it. …[Adhesive] tape’s no good anymore,” I complained, trying to use it to mark the Oscar magazine.

Want a piece of tape?”

Yes,” I answered, “just a small one. …Real small one. …Inch.”

Let me know when your test is over when you get a chance,” Cernan asked, thinking the AGS Calibration was still underway.

It’s over.”

Oh, it is over?”


Why don’t you give me your numbers,” he asked.

Okay. Where’s that extra mag, first.”

Right here. Let me just write something on it.”


You got a place over there you [can put it]?”

Yes, I’ll put it away in just a minute.”

Okay. Give me your[calibration] numbers [for the AGS].”

540…,” I started through the Calibration numbers again.

The first one? Minus 0.3? I can’t read it.” Cernan could not read the plus or minus from his angle.

Minus [0000]3. …Plus [0000]7. …Plus all zeros. …Plus [000]32. …Minus [000]83. …Minus [000]63. …They all look all right to me.”

…Yes,” Cernan said and checked the limits between INITIAL and CALIBRATION, again, “that’s within that [limit]. That’s a little more than usual, but not much. Okay; pretty small [Deltas].”

While you do this,” I said, “I’m going to pick up [the communications configuration for LOS]. We got to go. …LOS is 111:48. We got about three minutes and you want to configure it [right for this pass].”

“Okay, Houston,” Cernan called. “Did you get the AGS Cal numbers?”

“Yes, that’s affirmative.”

“It all looks pretty good to me. 546 may have been a little more than spec, but it looks pretty good.”

“Okay, looks good here.” This basically completed the activation of Challenger as an operational spacecraft. From now on, we would be carrying out the actions she was designed to perform and evaluating her performance and readiness to land in the valley of Taurus-Littrow.

You can go ahead [with the communications],” Cernan said. “Since we are not LOS yet, I can target [the PINGS] for DOI-2.”

Here’s your helmet. Keeps [floating]. …Or is that my helmet? I think we’ve lost track of helmets.”

No. mine has got a name on it.”

“Jack,” Fullerton queried, “have you gone to an OMNI [Antenna]? If you have, go LOW BIT RATE.”

What’s the [right] OMNI?” I asked Cernan who had the Timeline Cue Card, but was still trying to keep track of Evans, visually. Then, I just went to the FORWARD OMNI and LOW BIT RATE on the PCM switch and this seemed to work.

He was down here a little bit ago,” Cernan speculated; he was in front of us, I think…”

“Okay,” I said. “We got you on an OMNI and LOW BIT RATE.”

“Okay,” acknowledged Fullerton.

Can we target (load) DOI[-2]?” Cernan asked me.

Yes, if you want.”

We’ll pick this up…,” referring to the Timeline checks of the Environmental Control, Reaction Control, Electrical Power, and Ascent Propulsion Systems’ pressures. (The RCS and ECS pressure gages are the middle rectangular instruments with white-on-black scales in each group of three at the top of panel 2 below the Caution and Warning lights in Fig. 8.33↑, respectively).

I check[ed] those (ECS and RCS) [but the] EPS and APS, I haven’t [checked].” I then finished the checks.

Recycle the [Caution and Warning circuit] breaker,” Cernan read. “Is your [Steerable Antenna] set for AOS?”

Where do you want it?”

‘MATCH THE INDICATED ANGLES’, at LOS. Did we just have LOS?”

Not yet. We’re on an OMNI,” I said after checking that we still had signal.


It’s TRACK MODE – SLEW,” I repeated, “and what’s the new angles?. …Plus 90 and minus 45?”

Plus 90 and minus 45.”

[Have to] be a little more gentle with this thing than the simulator,” I observed.

Okay, that’s LOS,” Cernan noted.

Just missed their GET [for AOS].”

Ron, do you still read us,” Cernan asked Evans.

Yes, Loud and clear – how me?”

You’re loud and clear,” Cernan replied.

Talking to me, Cernan then said, “Okay, Ron, I need some…”

[I’m] Jack,” I needled.

Jack, I need PCM LOW when you finish [with the Steerable].”

That’s LOW.”

Challenger; America. Do you read me?” Evans called, again.

Yes, we read you loud and clear.”

You’re still clipping a little bit,” Evans said. “All I got was the ‘clear’, but that’s all right.” He may have had his audio Squelch set to high.

Okay, Ron. We are reading you loud and clear.”

I got that part, loud and clear.”

[UPLINK] SQUELCH is ENABLED,” I continued, finishing off the pre-DOI-2 Preparation portion of the Timeline. This squelch setting would block space static.

Missing my call-out, Cernan repeated, “UPLINK SQUELCH – ENABLE.”


Descent Orbit Insertion – 2

Another comm check [call for],” Cernan went on. We just did [that]. I’ll load P30 [with the DOI-2 PAD].” P30 constituted the PINGS program for External Delta-V.

Okay, I’m ready for you.” I had copied the PAD for DOI-2 from Fullerton almost three hours earlier.

You all set?” I asked. The NOUN 33 display on the DISKEY asked for the TIG or Time for Ignition. “112:02:40.92.”

Cernan entered this TIG and PROCEEDed. “Okay.”

[NOUN 81 DELTA-V is] minus 0007.5 [fps for x], and the rest are all zeros.”

They give you a burn time on that?” Cernan asked.

Yes, 22 seconds.”

We’re low [at perilune], so they anticipated that.” This was a shorter burn time than we usually had during Simulations and would adjust our perilune at PDI to be closer to the original plan.

Evans interrupted with, “Coming up on 8 minutes [to the orbit Circularization burn]. …Mark it.”

Okay,” I acknowledged.

What else do you need?” Cernan asked.

They said [NOUN 42 would be]…61.5 and 6.7 [for apolune and perilune].” These altitudes above the lunar mean radius were in nautical miles. It had always fascinated me that Apollo had designed the spacecraft and rockets using the English system of measurements, flew in space using the nautical system, and worked on the Moon using the metric system.

Okay,” Cernan said as I pointed to the Delta-V for him to enter in the third register of NOUN 42. That’s pretty good. …[Minus] 7.5[fps for the Delta V].” He PROCEEDed to get the NOUN 45 information for the Time From Ignition for DOI-2 and said, “Clock (Event Timer) is right on.” I had set this timer earlier based on the ignition time Fullerton had given me. Cernan then PROCEEDed again to leave P30.

I am not in ORB RATE,” I said, emphasizing that we did not want ORB RATE as the DOI-2 required a specific attitude tied to our orbital path.

After verifying the following: thrust hand controllers were in JETS, NOUN 46 indicated the DAP was set properly, GUIDANCE CONTROL was PINGS, and MODE CONTROL (PINGS) was in AUTO, Cernan loaded the RCS THRUST program, P41, in the PINGS. P41 first requested that we load roll, pitch and yaw angles for a maneuver, and we loaded 00000, 08500 and 00000. With this attitude putting us on our backs with feet forward relative to the Moon and our orbital movement, the four RCS thrusters pointing in the minus x direction would be firing to give us a reduction in orbital velocity. With the maneuver complete, he hit ENTER to give us the NOUN 85 velocity to be changed (minus 7.5 fps in X). MODE CONTROL (PINGS) was then placed in ATTITUDE HOLD.

What do I need to put in the AGS, here?” I asked Cernan who still had the Timeline Book.

410 [needs to be] minus 5,” Cernan read, “external DELTA-V.” (He meant plus 5, as there is no minus 5 in the 410 options for burn routines.) To make it easier, I took the Timeline Book from him and set Addresses 373 with the Time to Ignition, 450 with the DELTA-V X of minus 0007.5 fps, 451 DELTA-V Y at 0 fps, and 452 DELTA-V Z at 0 fps. Entering 310 gave me a countdown clock that matched the Event Timer and the PINGS NOUN 40 display and 370 showed the velocity to be lost after ignition. Address 500 would show velocity lost in X during the burn.

For about five minutes, we listened to Evans as he talked himself through preparations for his Circularization maneuver and tried, unsuccessfully to get a visual on his burn.

…THRUST A is ON…You guys still with me?” Evans finally asked. This burn would use America’s big Service Propulsion System (SPS) engine.

Yes, sir,” Cernan replied, “we’re with you.”

Okay, at 17 seconds, …there’s ullage.…99 PROCEED. We have ullage.…Oh-ho! …now for shutdown! Oh-ho! Beautiful burn!”

Sounds great, Babe. You got circ!”

Okay,” Evans came back, laughing.

Did you get it? You did get it?” Cernan was trying to be sure because our DOI-2 would have to be delayed if America had not achieved the proper orbit for a possible Abort by the Challenger.

…Hey, did you guys get the word? The burn is complete. I’ll trim it up [with the RCS].”

Yes, sir. We got the word. The burn is complete, Ron.”

You in T/R (TRANSMIT/RECEIVE),” I asked Cernan since it was not clear Evans was receiving his calls.

Yes,” Cernan replied after checking his communications switch.

Ron, do you copy Challenger? We copy your burn.”

Okay. Burn is complete. And all good residuals [in all axes].”

Have at it, [Ron].” It never was clear that Evans was receiving Cernan’s comments.

Back to business in the Challenger, I said, “I’ll time it (the burn) [on my watch], Gene.” Timing the burn with my watch was the third backup after the PINGS and the AGS clocks.

Okay. …VERB 77…NOUN 40…” VERB 77 set the DAP in its ATTITUDE HOLD MODE and a NOUN 40 display on the DISKEY gave us the time from ignition (and would count down the burn time) the velocity to be gained, and the accumulated change in velocity during the burn.

At this point, something caught my eye as I checked our Range and Range Rates relative to America by looking at Addresses 317 and 440, respectively. “See, our Range Rates should be…”

What’s wrong?”

Nothing,” I decided. “I just wondered why they (the rates) had [changed]. …I never remembered seeing that there [during sims].  …You happy here?” I moved on, pointing to the Timeline.

Yes, I’m all set.”

[Zero] feet per second. …Does that sound right for Range Rate, right now,” I asked, still puzzled by something I had not seen in training.

Yes, you should be coming through about zero [on Range Rate]. He’s (Evans) at the other end of the [relative orbit] football?” Cernan said with some uncertainty in his voice.

Yes,” I said, not really convinced, as Evans had just done his burn relatively close to us.

Cernan quickly entered a NOUN 54 in the PINGS to get Range and Range Rate to America based on our state vector and read, “Minus 4.7 fps on the [Range Rate]…”

Okay, …[4.7] feet [per second] for that Range and…”

What you got for Range…”

That’s good,” I said, comparing the two computer readouts.

That’s pretty good,” Cernan agreed…“Okay. I’m set.”

Okay,” I observed, looking at the eight ball in front of me. “That’s within the dead band. …That’s as close as I can keep Y and Z. …Surprised they (Houston) didn’t call us on that. [They are] Not watching my AGS as usual.” Understandably, Mission Control concentrated on the performance of the PINGS until it was necessary for the AGS to take over guidance.

Ron,” Cernan called, “we’re 2:10 from the [DOI-2] burn.”

Okay. Copy that.”

Hey, let’s check your perilune after the [DOI-2] burn,” I suggested to Evans.

Cernan began to talk himself through the upcoming burn. “Okay. Okay, that’s (DELTA-V) minus. I’m in the attitude. I want to thrust down (minus X DELTA-V) on the hand controller. I’m in Jets [on the TTCA selector].”

Okay. I am [in Jets], too. I’ll time it (the 22 second, 4 jet burn),” I added.

Have a KEY RELEASE, there.” Here, Cernan referred to the possibility that P41 would not function properly and that we would have to delay ignition. Then, he went back to the normal sequence we would see. “That’ll (the DISKEY) go blank at Average g.”

Should I watch the thrusters [flag indications]? And if the [outside burn] limit is 30 seconds, if it’s a two jet burn, …after 30 seconds, we pitch 180 and…complete with the AGS.” I was reading contingency procedures from the DOI-2 Cue Card.

With this short burn, we’ll just take what we got at 30 seconds,” Cernan decided.

And…the less trimming you do, the better the AGS [state vector] will be,” I added. “You know, less pulsing [of the accelerometers]. But don’t let that scare you,” I continued, laughing.

Just want to see what kind of [performance we have], because I got four jets on there. …Here’s the terminator…We’re at a minute, Ron. And we’re burning right at the terminator, Ron.”

Ha-ha. Okay. I’m in a 70 by 54.7 [nm orbit].” Obviously, his orbit was not truly circular; however, Mission Control wanted it close to those numbers, anticipating that his orbit would truly circularize as predicted gravity variations took effect.

That sounds familiar,” I said, recalling our Mission Simulations.

Okay, the DSKY is blank,” said Cernan, indicating our DOI-2 burn would start in 35 seconds.

I want to thrust down – minus X,” I reminded myself in case I needed to back up if the PINGS and Cernan’s manual TTCA thrusting did not do the job.

Yes, sir, That way because we’re going that way,” Cernan confirmed, pointing forward. The burn would slow us down by 7.5 fps and thus lower our perilune altitude 180 degrees away on the other side of the Moon.

22 seconds.”

Have at it,” I said.

We’re burning, Ron.”

Beautiful!, exclaimed Evans.

0.7 [fps] at a crack (DISKEY update),” noted Cernan.

At 22 seconds, I said, “Well, that’s it,” I called out as the thrusters went silent.

Zero [on the timer] plus 0.1 [fps residual],” Cernan read from the NOUN 85 display. With this residual less than 0.2 fps, no manual nulling would be required.

Plus 0.1,” I confirmed from the Address 500 readout on the AGS DEDA. After Cernan entered VERB 82, I noted that the altitudes of our apolune and perilune were “61.4 by 7.0” nautical miles and okay.

Used a little ‘gas’ on that one, didn’t we?” Cernan said while looking at the RCS propellant gages. (Gage to the immediate right of the RCS pressure gage at the top of panel 2 in Fig. 8.33↑ marked by the orange arrow gives the percentage quantity remaining).

I guess your burn is complete, huh?” Evans asked.

Burn’s complete and GO, Ron. We’re in a 7 [nautical] mile perilune.”

Okay!, Evans acknowledged. “Your burn was complete.”

AGS [perilune and apolune, Jack]?” Cernan requested.

647 and 315 [give 6.7 and] 61.4,” I reported.

Great! Right on [with the PINGS].”

6.7 is what the ground predicted so…”

AGS is with you (the PINGS),” Cernan interrupted. “Let’s do a VERB [37 and go to] P76.”

Okay.” P76 would allow Evans to send us an update on America’s State Vector based on his guidance systems integration of his Circularization burn.

Ron,” Cernan called, “you got the word? You can update our [CSM] State Vector [in your PINGS].”

Okay. We’ll update your State Vector [from America],” Evans replied.

You got the P76 [called up] for him?” Cernan asked me.

Yes,” I replied, going to the PAD Fullerton had given me about an hour earlier. Go ahead. It’s [running]. …[Time of Ignition for NOUN] 33 was on time: 111:57;30.09.” This was the ignition time of the Circularization burn. I also needed to put the TELEMETRY PCM switch to HI.

Okay. That’s good. DELTA-V [for NOUN 84]?”

Plus 70.5 [Delta-V in X]. …Plus all zeros [in Y] and a minus 0.5 [fps in Z].”

Like that, huh?” Cernan asked after he loaded the NOUN 84 registers and before hitting PROCEED.

That’s it,” I agreed.

Okay,” said Cernan. He would hit PROCEED when Evans was ready.

Shoot!” I said as I went to the Timeline step to put the TELEMETRY PCM switch in HI.

What’s wrong?” Cernan asked.

I was in HIGH BIT RATE for the [DOI-2] burn,” I answered with a nervous laugh, because we…missed that [item after] AGS [Calibration]. Actually, I had confirmed that PCM was in LO when Cernan had asked about it during the set up of the S-Band communications at the last Loss Of Signal (LOS) from Earth. In the process of getting ready for this State Vector update, I appear to have just moved the switch to HI without registering the fact.

Oh, that’s all right,” Cernan said.

Well, it…means they didn’t get the data on the burn [on the onboard tape].”

I’m going out to PDI attitude,” Cernan decided, using the attitudes listed in the Timeline.

Okay. You ready to…”

Ron, we hold you in a (VERB 82) 70.1 by 55.0[nm orbit].”

That’s pretty good,” responded Evans. “I get 70.0 by 54.7.”

Okay. I am ready to give you the [State] Vector,” Cernan notified Evans. “Okay?”

I am in HIGH BIT RATE. Go ahead,” I informed Cernan and he PROCEEDed on the NOUN 84 in P76.

Should be a pen floating around,” I said. “Is that your pen?” I asked, pointing to a pen sticking to a Velcro patch in front of Cernan.

Yes. I’ve been putting it there.”

Next, we had to update the AGS to the PINGS again, so Cernan entered a VERB 47 AGS initialization routine which I followed with Address 414+10000 in the DEDA to do the update.

I guess you got your [AGS] update,” Cernan said.

Yes,” I affirmed, but to confirm the update, Cernan called up VERB 83 on the DISKEY, and I entered 317 on the DEDA to compare Range to America.

Okay, 71.3[nm]. How does that look – 71.3?”

That’s good,” I replied, and then entered 440 to check Range Rate.

And 71 feet per second,” Cernan read off the VERB 83 display.

Okay,” I said and asked, “Happy?”

Yes. Okay, you can go [TELEMETRY] PCM – LO AND 373 [for PDI Time of Ignition].

Okay. Well, I got a new one (TIG) on that somewhere [in the PADs].” Again, I went back to Fullerton’s last PAD and entered 0182.0 in AGS time. Then, with a 410+00000 entered in the DEDA, I put the AGS into its Orbit Insertion Routine that would be used if we had an Abort during Powered Descent and had to use the AGS for rendezvous with Evans.

I’ll go into the [P63] Algorithm Test,” Cernan declared, but then hesitated. I’ll wait until you for sure get a good High Gain [lock] on them; otherwise, we’ll screw that thing up. Okay?”

Okay. How long to AOS?” I was concerned that this P63 Algorithm Test in the Timeline was to be finished well before AOS and we would have a lot to do once Mission Control came back on line. For some reason, Cernan hesitated to do the test without Houston watching. Apollo 10’s activities in the cabin prior to the first Descent Engine burn by Snoopy had been quite chaotic and this experience may have colored his decision. We never delayed the Algorithm Test during Mission Simulations as far as I can recall. This critical test would determine the PINGS readiness to start the Descent Engine and required temporarily entering P63, the Breaking Phase program for Powered Descent.

As required after the as yet to be performed Algorithm Test, Cernan set up the Digital Auto Pilot (DAP) for Powered Descent. He put the PINGS in idle, P00, entered VERB 48, and set the DAP register at 22112 on DESCENT – 4 JET; 20º/sec SCALE; 1º ATTITUDE DEADBAND; 2º/sec ATTITUDE RATE; and BYPASS for both the Auto Throttle Check and the monitoring of Abort Push Button (The latter creating the problem found on Apollo 14 by a solder ball in the Abort Button.). A PROCEED set the DAP and a VERB 34 terminated VERB 48 activity.

Oh, it’s (AOS) 25 minutes.”


We got the next milestone. …We’re counting down to PDI. …In case you’re interested, America, we got 41 minutes to PDI,” Cernan told Evans.

Ah-ha. Okay!”

Well,” I observed, “I’ve lost two things: a pen and a right-angle bracket [for the Hasselbald camera].”

For the mirror up there?”

No, the…Oh, here it is. Here’s the right-angle bracket. Never took it off.” I previously had begun to set up the cameras for Powered Descent and Landing.

Use my pen.”

Well, I just hate to have anything lost,” I complained, and then put a new film magazine on the DAC, setting at f/2.8, 1/500 shutter speed, and 12 frames per second. I mounted the DAC in the bracket above my window where it would film the landing…if I remembered to turn it on.

[I don’t want to use] the used magazine, …[that is] a partially used magazine, in this case.”

Let’s try and mark some of those magazines,” Cernan repeated, “so we’ll know which ones are which.”

Yes. You got that one didn’t you?”


You marked that one?”

Yes, I marked it: ‘Undocking Lunar Orbit’.”

And the landing site [footage], too, on that.” This was filming of Taurus-Littrow made during the close approach earlier in this orbit.

Yes. Yes.”

And, let’s see,” I said, looking around the cabin, “I don’t see the fountain pen. …Okay,” I continued, looking at the Timeline Book. You got the [P63} Algorithm [Test].” My concern was that we would be pushing it to have Mission Control insert a new state vector (with Evans’s landmark sighting data) into our guidance system in the 16 minutes between AOS and  PDI.

Not yet.”

Getting up to attitude here.”

COAS is in the OVERHEAD WINDOW?” I asked. This was in preparation for a LM active docking in the event of a landing ABORT.

Yes, sir.”

Okay…restraints?” I read from the Timeline. We had attached the restraints to our suits earlier for stabilization in the cabin. “Then you’ll go INERTIAL [for attitudes on the eight balls].”

FDAIs (i.e., the eight balls) are now INERTIAL,” Cernan reported. “Why don’t we put our helmet and gloves on?”

I think that’s a good idea,” I replied, thinking that we needed to get ahead in the Timeline if the Algorithm Test were going to be delayed until after AOS. I grabbed my gloves and, this time, had little trouble putting them on and locking the wrist rings.

You do that pretty quick,” Cernan observed.

‘Gene Cernan’,” I said, reading from the label in the helmet I handed him.

I’m not ready yet. Wait.”

How do you read, Gene,” I asked to make sure my mike position and comm configuration were okay before the helmet went on.

Cernan gave me a thumbs up and then bragged, “Look at that! I put it (Challenger) at attitude, and it didn’t even tweak it.” Cernan had called up P63 in the PINGS and put PINGS MODE CONTROL to AUTO. This would have allowed the PINGS to maneuver to the PDI attitude had he not previously gone there manually.

Then Cernan added, “Jack, if we have to ABORT, it’s VERB 21, NOUN 46, ENTER, ENTER.”

Right. Let’s don’t do that though.” Cernan actually had misspoken. The first Abort entry in the DISKEY was VERB 22, not 21, that would let NOUN 46 switch the DAP configuration to its “Function Fail Mode”. This entry, however, came after four rapid preceding steps, spelled out in both the Timeline Book and on the ABORT Cue Card. (ABORT STAGE – PUSH; ENGINE ARM – ASCENT; ENGINE STOP – RESET; and ENGINE START – PUSH, then followed by the VERB 22, NOUN 46 – ENTER, ENTER, and finally, by both MODE CONTROL switches to AUTO.) I am not sure why I did not go through this with Cernan at this point – probably just assuming, in the focus of the moment, that an ABORT would never happen. I am surprised at this, as I should have been more diligent. (The Abort Stage is the black-with-white letters pushbutton surrounded by the yellow and red striped square to the lower right of panel 2. The Engine Arm switch is the leftmost in the group of five outlined as Engine Thrust Control in Fig. 8.22↑ (i.e., lowest yellow arrow below the red ones). The Engine start/stop/reset pushbutton was shown in Fig. 8.24↑.)

Yes. Let’s not,” Cernan added, “…I think I’ll get a sip of water.”

That’s a good idea. I think I’ll do that, too. …I’m glad you thought of that. …Camera is set. …You need any more [water]?”

No,” Cernan replied, “why don’t you jab me with a little LCG [cooling], though.”

Okay. Before we go down.” One valve behind my left arm controlled LCG cooling for both of us.

Man, that’ll hold you down,” Cernan exclaimed as he checked his restraints. “Holy Smoley. Man! I think they’re ready to hold a 2000-pound moose down with that. Want to check it?”

Okay. …Now, [squat] down [a little].”

Okay. …You cold enough.”

Yes,” I said with a laugh.

So am I.”

After a few minutes more putting on gloves and helmets, I reminded Cernan, “We didn’t tell them (Mission Control) about those leak checks.”

About what?”

About barely passing the REG checks or the integrity check. …We can talk to them about it later, I guess,” I said, implying that we could do this after the mission was over. No need to get them excited prior to Powered Descent.

Roger,” Cernan said with a laugh, understanding my implication.

I’m not going to put it (ATTITUDE/TRANSLATION CONTROLLERS) in pulse (4 JET), if I’m not firing any thrusters.”  Cernan was reading ahead in the Timeline to make this comment. Again, he seemed to be looking for a way to show independence from the Checklist. This configuration for the hand controllers meant that if he or I had to control RCS attitude and thrust manually, the switches would already be set properly. I was glad he told me that they would not be so set. (The ATT/TRANSL switch is the 4th of the 5 switches, counting clockwise from the top left switch in the group of five in the area marked Engine Thrust Control below Cernan’s 8-ball in Fig. 8.22↑. It is the one without the rubber cover. ‘4 Jets’ is the up position of that switch; and ‘2 Jets’ is down).

Here, they (the jets) really don’t seem to be [needed],” I responded. “…Okay. …Where do we stand?. ..Hey, I got to get the Ascent Batteries on line.”

That [done] going down to PDI?”

Yes, sir. 30 minutes to PDI. …Well, shoot.” The Timeline actually called for the Ascent Batteries to come on line at 35 minutes before PDI, so I put them to NORMAL FEED at this point since we were behind about 5 minutes.

Okay,” Cernan said, going back to scanning the Timeline. “You want to do some INVERTER – 1 switching, too, here.” Closing a breaker on his Panel 11 would take care of this. “Yes, and we want to do some of these things there, too.”

Let me see [the Timeline].”

Got to do a lot of things here [with the ECS],” Cernan observed. “…Let me give them to you.”

Okay. Let’s go.”

Helmets and gloves ON. CABIN REPRESS – CLOSE.”

REPRESS is CLOSED. …Oh [you mean] the valve.” I had first checked the circuit breaker by the same name.

CABIN REPRESS – CLOSED,” Cernan repeated.

Okay. It’s CLOSED.”






Going to EGRESS. …They’re both EGRESS.” These valve positions set us up for being suited up for Powered Descent in case anything should happen to depressurize the cabin. The general rule of whether we would be suited or not was to be suited for any change or potential change in the configuration of the stacked spacecraft. An Abort would change that configuration.

Okay. [Now,] Pre-PDI Switch Setting [Check],” Cernan continued. “VHF ANTENNA –FORWARD.”


My INVERTER breaker’s CLOSED. Select INVERTER number 1.”

Mine’s [already] CLOSED. INVERTER 1 [selected].” Although Cernan’s panel had the circuit breaker for INVERTER 1, the switch to select between 1 and 2 was on my EPS panel next to my right arm.


It’s RESET,” I stated. The AELD (Ascent Engine Latching Device) would insure that the propellant valves would stay open, once opened, until the Ascent Engine was specifically commanded to STOP. It was this AELD function that made it possible, in an extreme series of failures, to use jumper cables attached to specific circuit breakers to ignite the Ascent Engine. The AELD also automatically set RCS thruster Control to 4 JETS and NARROW DEADBAND during an AGS Abort. Cernan’s ENGINE STOP PUSH BUTTON was in front of him to the right of his left, throttle hand controller (Fig. 8.24↑) and mine was to the left of the AGS DEDA display (Fig. 8.8↑). A cover with a guarded lever release mechanism covered both Push Buttons to prevent inadvertent activation. (In Fig. 8.24↑, the safety release mechanism is the housing just beyond and slightly left of the START/STOP button. In Fig. 8.8↑, the L-shaped grey cover above the square, green Velcro pad houses the ST(ART)/STOP pushbutton partially hidden by the left yellow hand grip. The yellow safety lever release mechanism is on the top of the cover).

And the [Caution] light’s out. …Set the window bars.” These horizontal bars crossing the windows would prevent anything that might get loose in the cabin from breaking the windows. “On [Panel] 16, STAB/CONTROL –AELD [circuit breaker] – CLOSED.”

AELD is CLOSED,” I responded. This circuit breaker established redundant power to the Ascent Engine Latching Device.

On 16, ABORT STAGE [circuit breaker] – CLOSED.” Now, a command to drop the Descent Stage and continue an Abort on the Ascent Stage had redundant power.


CYCLE CWEA [circuit breaker] and get BATTERIES 5 and 6 NORMAL FEED – ON.”

They’re ON.”

What time were they [turned] ON?” Cernan asked.

They were on [at] 30 minutes. Make it 31 minutes, before [PDI].”

So that’s 2 minutes ago. …That’s 112:19.”

That’s late.” I pouted. “They’re going to be mad at me [at the LM CONTROL console]. …CYCLE CWEA [breaker], you said?”



Why don’t you pick it up here [in the Timeline Book]?” Cernan asked as he handed me the book.



TTCA (left hand controller) THROTTLE – MINIMUM.”

Okay. That’s a good point.” Here, Cernan referred to the fact that the PINGS would start the Descent Engine at minimum thrust. If we had to switch to manual control in an early Abort, we would want to match that thrust level rather than have a spike. “THROTTLE – MIN,” confirmed Cernan.

And the LMP’s [TTCA] going to soft stop [as well]. …RATE SCALE – 25 DEGREES PER SECOND.”

25.” This related to the roll, pitch and yaw rate needles normally resting just outside the eight balls.


4 JETS.” Any automatic or manual commands for attitude change during Powered Descent or an Abort would use all available RCS jets needed to execute those commands.

Okay, let’s look at the [pressures and consumable levels for] the DPS, the APS, and all those things (RCS, EPS). Check your switch guards.”

Okay, I’m happy with them,” Cernan said. Three switch guards had to be checked. The first prevented inadvertent activation of the STAGE switch on the Panel under Cernan’s left arm that would fire the explosive cutters to separate us from the Descent Stage (yellow zebra-striped cover in Fig. 8.10↑). The others guarded the two ENGINE STOP PUSH BUTTONS on Panels directly in front of our stations in the cabin as just described above with Fig. 8.8↑ and Fig. 8.24↑.

I began to check the various pressure and quantity gages by moving the appropriate rotary switches and checking the gage readouts. “DESCENT…tanks – 3110 [psi for fuel and] 3130 [psi for oxidizer]. …ASCENT [2 is] 150 [psi] and [ASCENT 1 is] 115. …Okay, it’s (rotary switch position is) back to SUPERCRITICAL [pressure].” As the latter showed the fuel and oxidizer pressures in the “Start Tank” for the DPS, this would be the initial parameter we would monitor. “RCS [pressures and quantities] look beautiful.” (The 3 tape meter gages at top left of panel 2).

ECS and EPS?” asked Cernan.

I’ve done that [check] once; we’ll do it again. …[First, note that the] ASCENT [system] looks good, [but] ASCENT 1 [pressure] is lower than ASCENT 2. We’ll keep an eye on that one. …Okay, ECS. We’ve got that? [O2] Pressures are good. Glycol [temperature and pressure] looks good. (the two Glycol temperature/pressure, and quantity tape meters are to the immediate left of the panel 2 cross-pointers in Fig. 8.33↑, not marked) Temperatures are okay (ECS temp and press gages are just above the glycol gages). …ED BATTERIES are good, Geno.”

Okay, ED BATs good, and everything else good on EPS?”

Yes, except the ASCENT BATTERIES are a little cold, probably,” I acknowledged.

Okay, let’s pick up [the pace],” Cernan continued.

I wonder if I ought to go ahead and…take some Descent Batteries [off line]…,” I speculated, thinking that transferring load to the Ascent Batteries would warm them more rapidly.

No leave them on. You’re only three or four minutes late.”

Yes. They wanted it earlier, though. …That’s why I had that note [hand written in the Timeline].” I was only a few minutes late bringing them on line; this concern on my part may have been misplaced, but later LM CONTROL would ask for more battery load to be added.

Okay. Let’s go over to the DPS [Cue] Card,” Cernan continued.

Okay…DPS burn: Circuit Breaker DECA GIMBLE AC [on Panel 11] – CLOSED.”

Okay, DECA GIMBAL – AC is CLOSED.” This breaker supplied power to the engine gimbal through the Descent Engine Control Assembly and allowed both automatic and manual control of the orientation of the engine nozzle and therefore the direction of thrust. “AC” indicated that this breaker came off the AC electrical bus.

…My DISPLAYS and OVERRIDE LOGIC breaker is CLOSED [on Panel 16]. …ALL STABALIZATION/CONTROL [breakers] CLOSED [on both Panels] except AEA [on yours].”

All are CLOSED except AEA (Abort Electronics Assembly),” Cernan confirmed. AEA power would be left off line until later to avoid any accidental ABORT.

And check your LOGIC POWER [circuit breaker].”

LOGIC POWER breaker is IN.”


25,” Cernan confirmed. Some of these items merely double checked actions we had already taken.



AUTO/COMMANDER,” I confirmed, laughing. “I read that wrong every time.” The Cue Card actually has both configurations for that switch next to each other with the second labeled for “PDI.” The MANUAL/COMMANDER position would be used for a contingency burn of the Descent Engine.

I continued the Cue Card: “ATTITUDE/TRANSLATION – 4 JETS.”

4 JETS.”


It’s ON.” This switch enabled the RCS firing logic that controlled cross-coupling between thrusters that otherwise would have changed velocities rather than just control attitude.


ENGINE GIMBAL is ENABLE.” (The Engine Gimbal enable switch is marked by the dark green arrow in the top leftmost corner of panel 3, Fig. 8.33↑, left of the radar signal strength meter, marked by the white arrow).


It’s OFF.” The PINGS would control the Descent Engine thrust and thrust direction during Powered Descent.


Okay. They’re both RESET.”

Looks good,” I commented, as these two push buttons next to each other to the lower right of Cernan’s eight ball might save our lives if a serious problem arose with the Descent Engine during Powered Descent. (Fig. 8.33↑, circular and square push buttons surrounded by the yellow and red striped tapes).

DEAD BAND – MINUMUM,” I continued



They’re MODE [CONTROL].” These positions on the ROLL, PITCH and YAW switches allowed the PINGS to control attitude with the RCS if that became necessary, although normally positioning of the Descent Engine thrust direction would control ROLL and PITCH during Powered Descent.

MODE CONTROL – PINGS – AUTO…and AGS – AUTO. You’ll get that later.”

I’ll get them when we go into [P]63.” As mentioned, Cernan had delayed the PDI, P63 Algorithm Test until we could let GUIDO in Mission Control watch our telemetry.


They are RESET.”



We’re standing by for the rest of the Checklist,” I asserted. Except for the Algorithm Test, we had gotten ahead of the Timeline by a few minutes. This illustrates, clearly, the value of Checklists in maintaining crew discipline that had been missing during a similar period Cernan experienced on Apollo 10.

[When] we come around the horn, we will both go VOX (Voice Activation Comm) and you can pick up [S-Band High Gain]. …Okay, there it is. Zero, plus 0.1, and 7.0 fps.” Cernan had called up VERB 82 to be ready to report residual Delta-Vs for the DOI-2 burn when Fullerton came back on line. “Can you get that? I can’t reach around there to…Okay, Babe. Let’s go do it!”

You want to look at the [PDI] RULES[38]?” I asked, looking at the next emphasized item in the Timeline.

Yes, let’s talk them over. …I’d like to do it (land) anyway,” Cernan laughed, “rules or no rules.” This is why I planned to have an altitude update for the AGS. If Cernan was going to break the rules, let’s make sure he can do it safely. “…Let’s have some [Landing] Radar, that’s what I want to have. Everything else can be beautiful and the Radar isn’t. …[That] may not make a very nice day out of it. …Boy we’re sub-solar, now!” Cernan had looked out on the surface and saw no shadows with the Sun directly overhead.

Okay.” I began, “[we] require AUTO – ULLAGE to AUTO – ON.”

Okay.” Mission Rules allowed us to back up either the ullage or the Engine On, but not both.

If you don’t have either one” I continued, “we got to go to my EMERGENCY CARD…[that is] after PDI.” This Cue Card gave the set of procedures necessary to secure and safe the systems so that Mission Control and we could assess them and decide if we were going to try again.

[You mean] after we start?” Cernan meant after ‘PDI ignition time.’

[Yes, we need] one (Ullage ON) or the other (DPS ON).” Either the commanded automatic ULLAGE or the Descent Engine igniting would mean the PINGS is functioning properly in P63, the Braking Phase of Powered Descent.

I pressed on: “PDI plus 31 seconds: That’s the max[imum] burn time for Number 2 [ABORT] opportunity. And a max time without full throttle (DPS thrust) [if we are going to land]…31 seconds.” Number 2 Abort opportunity would be a direct rendezvous with America.

Thirty-one seconds,” I repeated to help seat this critical number in our minds. “Landing Radar [data]: if…[data is] accepted [by the PINGS] and converged by P64 [starting], you’re GO. If it’s accepted and converged in P63 and lost and regained in P64, you’re GO. And if it’s accepted and converging and does converge in P64, you’re GO.”

Okay.” P64, the Approach Phase of Powered Descent, would begin at about 9 minutes and 30 seconds after PDI and would initiate the pitch-over at about 8,000 feet altitude (Hi-Gate, Fig. 8.34↓) that would allow us to see the landing site.

Now, if it’s (Radar) not accepted by the LGS (PINGS), then [the] max[imum] DELTA-H (altitude difference) is 1500 feet. That’s [DELTA-H] between the PINGS and the Radar [altitude shown on the Tape meter].”

Okay.” This Rule meant that, with the Landing Radar locked on the lunar surface and feeding altitude data to the Tape meter (large rectangular gage immediately to the right of the 8-ball in panel 1, Fig. 8.33↑), we could try to get the radar data accepted by the PINGS until there was a difference of more than 1500 feet between that data and what the PINGS thought our altitude was based on its state vector. On the other hand, if Landing Radar Data have been incorporated in the PINGS in P64, but subsequently the PINGS stopped accepting that data, we could continue to a manual landing provided that the Radar (tape meter) altitude and the PINGS altitude differed by less than 1500 feet.

[If there is] No Landing Radar, we ABORT.”

Evans, who had already acquired radio contact with Mission Control due to his higher altitude, interrupted.

Go ahead, Ron.”

A cross-check with Houston prior to PDI, and we’re not going to bother you unless you want to say something. Looking for you, …[but I’m] not going to say anything unless I call you.” Evans meant “unless we call him”.

Sounds good,” Cernan replied.

Okay [to continue with the Rules], Gene?” I persisted.


We’re GO to 10,000 feet if they don’t give us a Radial NOUN 69. We’re going (GO) to 6,000 feet if we get the NOUN 69, if there is no Radar.”


[This rule reflected the case where Landing Radar data was not being incorporated prior to a PINGS calculated altitude of 10,000 feet, but Mission Control could give us an altitude update (Radial NOUN 69) based on its tracking data. Then we could continue to 6,000 feet in hopes that the PINGS would finally incorporate the Radar data. In all of these tradeoffs, we also would be making a comparison of the difference between the altitude rate (radial velocity) as shown by the PINGS and the AGS. Without a NOUN 69 update, the limit was a difference of 10 feet per second, while, with an update, the limit was 20 feet per second. Mission Control also could update our forward (X) and cross-range (Y) velocities through NOUN 69 entries; however, limits existed on how much of a difference there could be between the velocities displayed by the PINGS and those determined by Doppler tracking from Earth.]

If there is no PINGS, we ABORT after High Gate [where P64 replaces P63) unless [the PINGS goes out] after High Gate.”

Yes, unless after High Gate,” Cernan repeated. In this case, the rule would have us abort whenever we lost the PINGS.

Thrust: You’re NO GO if the GTC (Guidance Throttle Command) is not decreased to 57 percent by P64 plus 15 seconds.”

Okay.” NOUN 92 in P64 would give computer’s commanded throttle in percent as well as the rate of altitude change and the altitude. The Engine and Commanded Thrust levels also could be read off opposed needles on a gage just above the Landing Radar Altitude and Altitude Rate Tape meters. (Fig. 8.23↑).

That’s NOUN 92,” I reminded Cernan. “Bingo [minimum] propellant [comes] 1 minute 31 seconds after Low-Level [warning]. Our lowest propellant quantity equals 2 percent. …And there’s some silly thing about Radar flashing lights here.”


Flashing Landing Radar Altitude or Velocity Lights preceded by a steady Landing Radar Light with Altitude Lock-On below 35K [feet], you cycle the circuit breaker [for Landing Radar on Panel 11]”

And I don’t fully understand that one. Never have,” Cernan asserted. Fortunately, Mission Control would be keeping track of the Powered Descent Rules, as Cernan and I clearly would be more focused on the landing rather than continuously comparing various systems’ parameters.

Boy! I tell you. These books aren’t going to stay here [in this pocket].” With the review of Mission Rules complete, I went back to policing my part of the Challenger.

[I had begun to organize a few things before AOS came and our lives really became hectic. Most importantly, I set the S-Band OMNI Antenna to FORWARD and set the pitch and yaw angles for the Steerable (High Gain) S-Band Antenna, putting its TRACK MODE to SLEW so once we had a lock-on it would track the signal from Earth. If there was one sure way to force a one orbit delay in landing, it would be to have trouble getting state vector updates from Mission Control. The VHF B TRANSMITTER was turned OFF, the BIOMED Telemetry switch went LEFT so Cernan would be transmitting his heart and respiration rates during Powered Descent, and the PCM data rate went HI. From a biomedical stress point of view, however, I am not sure what is worse: having the responsibility for landing or having someone else have the responsibility for landing.]

Do you want to help me out with this [Event Timer], Jack?”

Oh, I’m sorry.”

Okay, I got the hack. Wait a minute. …There we go. Got her. …[You] happy with all your ECS [settings] behind you?”

Yes, sir.”

Circuit [through] it again. We CLOSED on REGs, EGRESS, EGRESS,” Cernan said, possibly a little nervously, as we had just finished going through this part of the Timeline carefully.

EGRESS, EGRESS,” I confirmed.

AUTO,” he said, checking the THROTTLE CONTROL switch, again. “We’re all set, …Can you get into there, [the side pockets]? Put those [books] in there. We’ll get them if we need them. …Okay. When we come up, I want to be S-BAND ANTENNA [OMNI] to FORWARD.”

It’s there,” I confirmed, having set the communications up for AOS after going through the PDI RULES. “Minus 33, plus 54 [for the Steerable Antenna pitch and yaw.]. …Okay. We’re ready. Where do you want that,” pointing to the HELIUM PRESSURE MONITOR rotary switch, “on SUPERCRIT?” This showed helium pressure in the start tank for the Descent Engine. (Fig. 8.25↑, the rotary switch just above and to the right of the two yellow arrows on the corner of panel 1).

Yes, Jack.”

I’m getting just a little glare off of there (the front panels), but I think it’ll be all right [as we get the sun behind us].”

Well, it’ll change as this window [sun beam] changes here. …Come on Challenger, do your job.”

Okay, 32 minutes,” I noted. “Three more minutes [to AOS]. I’ll be in UPDATA LINK in DATA. …Got a little bit of an X-axis accelerometer [bias] but very slight. Changing very slowly. …All of my accelerometers are changing.” I was looking at AGS Addresses 540, 541 and 542 for this information on how the accelerometers had performed since their last update from the PINGS.


Okay, Houston, what we’ve really got [is everything] smooth coming around,” Cernan said, I guess to himself.

Say again,” I said, puzzled.

I say, AOS on down is where we really got to be with them.”

Yes. …You know, we’re starting right in plane according to the AGS. No out-of-plane velocity [relative to the landing site].” I had called up Address 263 to get this information. “Let’s make sure we get them [locked up on S-Band] before we go VOX.”

So it doesn’t screw it up.”

Yes. …Okay, I’m watching [S-Band signal strength],” I said. “Have at her.”

That’s going to do it, Babe.”

I don’t want to have to touch a thing,” I commented, laughing at the possibility that we would not need a state vector update. “Just tell me where we are, yes, sir.”

Do you want this, Jack?” Cernan said, offering me the water gun for a drink.

Well, yes; maybe I better.”

You’re writing NOUN 69 or something down?” he asked.

Yes.” NOUN 69 gave us the current PINGS correction components for Downrange, Out-of-Plane, and Altitude relative to the Landing Site. Recording these before GUIDO’s state vector update would tell us how well the PINGS had performed since the last update.

You need a piece of Velcro right there [to hold that pen]. That’ll be all right.”

Okay, we’re there [with signal strength]. Going to High Gain [Antenna].”

We got AOS?”

Yes. …There it is,” I answered.


I do not recall being nervous as we approached the start of Challenger’s landing in the valley of Taurus-Littrow. 30 months of combined training with Dick Gordon for Apollo 15 and Gene Cernan for Apollo 17, time spent with the design and test engineers, great and frequent interactions with the team in Mission Control, and the discipline provided by the Timeline that we had refined for this mission, developed confidence that I could do my part and help Cernan do his. This confidence masked the concerns others and I had about Cernan’s ability to maintain continuous focus on the job at hand. Only occasionally, and never at a critical moment so far, had he seemed to show the occasional impetuousness and recklessness he was known to have[39].

Cernan already had flown as the Lunar Module Pilot on Apollo 10, and understandably felt he knew my job better than I did. That is a debate that will go unresolved, but I would have been less than a typical astronaut and pilot if I had agreed with him on that point. I had lived with many aspects of the development and test of the Lunar Module and with the formulation of procedures for its operation and malfunction analysis if there were problems. Training for Apollo 15 as the Backup Crew Lunar Module Pilot, as well as for Apollo 17, put me at the top of the wave of the knowledge and the procedures for that position. Benefiting from all the missions that had gone before, I suspect that, with the exception of Fred Haise, Lunar Module Pilot on Apollo 13 and long time astronaut representative at Grumman Aircraft’s manufacturing plant, I knew as much as anybody about the engineering and operation of this remarkable spacecraft.


Okay, Houston,” I called. “This is Challenger. How do you read? We’re HIGH GAIN and DATA.”

After no response, I called again. “Hello, Houston. How do you read Challenger?”

Do you have an Earthrise?” Cernan asked, meaning could I see the Earth.


Oh, whee! That’s pretty. …How’s the High Gain?”

We just lost it (signal strength). Along with the OMNI [Antenna signal],” I answered with some concern.

Let’s get that High Gain as soon as we can,” Cernan said, unnecessarily. I understood the time critical need for communications as well as he did.

It’s their problem, I think,” I answered, quietly. Having a good signal at our end and then losing it on both antennas indicated that the uplink carrier signal had been dropped. Nothing we could do about that.

“Hello, Houston,” I called, again. “How do you read Challenger on an OMNI right now?”

“Okay, Challenger,” Fullerton answered, “you’re loud and clear on the OMNI. How did it (DOI-2) go?” The question surprised me, as the timing of AOS would have told Mission Control that we had had a successful DOI-2 burn. Maybe GUIDO did not bother to tell anyone else.

“The burn was GO. We’re in a 7-[nautical] mile perilune on the PINGS, and we had 0, plus 0.1, and plus 0.1 residuals [in x, y and z axes].

“Okay, sounds good.”

“Okay, Gordy, I’m going to try the High Gain [Antenna, again]. I had you locked up once, and then I lost you. Let me try it again.

“We concur. Go ahead, Jack.”

“Okay. There’s the Omni back,” I said, noting that signal strength was back up. …Okay, Gordy, that’s my fault. I didn’t know you were up-linking. You’ve got the OMNI, and I’ll leave it.” Actually, it wasn’t my fault. GUIDO should have told us they had started the up-link.

“Okay, we’ll stay on the OMNI for the up-link,” Fullerton replied.

He should have given me a call,” I said to Cernan. “I didn’t know they were up-linking that quick. They never have in the past.”

Okay,” Cernan replied, and then asked, “You need your [AGS update] and ED BAT report?”


You can give that to him now.”

“Okay, Gordy, ED BATS are 37.5, both batteries. The Ascent Battery ON time was 112:19:00, about four minutes late.”

“Okay, Jack. Copy.”

“Jack, we want BATTERY 3 – OFF for preconditioning [of the Ascent Batteries].”

“Roger.” I had recommended doing this when I was late putting the batteries on line, but was over-ruled by the Commander.

And we’re getting back down among them, Gordy,” Cernan said, but did not key his mike.

Challenger,” Fullerton called, “We’d like you to verify that the DEMAND REGS are in EGRESS.”

“Yes, they’re in EGRESS,” I reported after checking behind me once again. “That’s verified. …And do you have a 231 update [for the Landing Site Radius]?”

“Stand by,” Fullerton said as he checked with GUIDO. “Negative. No change, Jack.”


“Gordo, how do you read CDR on VOX?”

“CDR, you’re loud and clear on VOX.”

“How do you read the LMP on VOX?”

“Loud and clear, Jack.” As was my initial intention, we had been using PUSH-TO-TALK keys attached to our oxygen hoses.

“Gordo,” Cernan began, “up until this time, the bird has looked beautiful – perfectly clean. All the checks have come out just as advertised.” He neglected to say that he had skipped the P63 Ignition Algorithm Test. I had not brought it up again, because he had looked at P63 to set the event timer and to compare the PDI attitude he had flown manually with what P63 said was needed. At least P63 seemed to be functional.

“Okay, sounds good.”

“And we’re looking at 9 minutes and 5 seconds from PDI,” I reminded everyone. A lot remained to do.

You get all these?” Cernan asked pointing to the communications set-up in the Timeline Book.

Yes, I got it.”

Challenger, do you see a VERB 33 out of [the] DISKEY? If you do, ENTER it.” VERB 33 on the DISKEY without input from us also indicated completion of GUIDO’s uplink.

“Okay,” I replied, “it’s there, and I will ENTER.”


“Okay, it took; and I’m showing P00.”

“Okay, [its] your computer; the up-link’s in.”

“Okay, we’ve got a tone on the UPVOICE BACKUP.” This meant that Challenger had a state vector that incorporated the landmark sighting data Evans obtained on the last orbit. Now, we had the full guidance capability to land safely in Taurus-Littrow. If all the hardware and software did their things, we should be on the surface of the Moon in about 22 minutes!

“VERB 47 coming in at you, Jack,” Cernan said as I moved to update the AGS with the new state vector.

“Okay, hit it,” and then I entered 414+10000 in the DEDA. “Okay, I got it (the update)…240…wait, [load] 231 (Landing Site Radius) 56900, that’s supposed to be…Okay.” Address 240 is the Challenger’s X Position Component and for an Abort would be equivalent to the Landing Site Radius. “Okay, 254 (Challenger’s Ephemeris time) is plus 01944. …Okay. … Okay, 262 (Z Velocity Component) is minus 00143. …Okay, 400 plus 30000 (IMU Realign), and I will watch it.”

“How’s it look?”

“It’s had that all the way along – a little bit of roll bias.”

“Okay. That’s good. 400 plus 1.”

“400 plus 10000 is in.” This restored the AGS to Auto Guidance Steering, if needed. To check that the AGS was ready, Cernan put the MODE SELECT switch to AGS which activated the steering needles on the two eight balls.

“Okay, and we do have your needles,” he confirmed.


“Okay, and there’s a VERB 83 looking at you. Our CROSSPOINTERS are LOW MULTIPLIER for you. Okay, and there’s VERB 83. Give me a 317 and 440.” Cernan, slightly out of sequence with the Timeline, but of no matter, entered a VERB 83 in the DISKEY, and I called up Addresses 317 and 440 to compare the two computers calculations of Range and Range Rate relative to America. As expected, they were the same, but this verified that the AGS had the new state vector.

Challenger, Houston. We’d like you to try the High Gain [Antenna] once more. PITCH is zero and YAW is 59.”

While I reset the pitch and yaw for the S-Band Steerable Antenna, Cernan asked, “Are you happy with this [AGS check], Jack? …Let me go to P63.”

“Yes, go ahead.” We would finally get the full P63 Algorithm Test, but now as part of the real thing. Not doing this test earlier was a big deal in that if we had seen a problem, we and/or Houston could have worked any problem and possibly avoided a delay in PDI.

“Gordy,” Cernan called, “[I] understand that no NOUN 68 prior to P63, or [rather] no NOUN 69, right?” Understandable nervousness from the cool pilot astronaut?

“That’s affirmative.” In case the uplink from Mission Control had been unsuccessful, NOUN 69 would have allowed a manual entry of Mission Control derived corrections to the Range, Cross-range and Altitude of the landing site based on Doppler tracking. Even though we had the uplink, it never hurt to ask GUIDO to think about it one more time.

“If you don’t need to ask him anything, I’ll try to get the High Gain.”

“No. Go ahead; try it,” Cernan agreed.

“Try the High Gain, Gordy,” I requested. “It’s locked up in AUTO.”


“And, Gordy, be advised that you’re clipping on your first word.”

“Okay, Jack. We’d like you to set 410 in the AGS to all balls – plus all balls.”

“That’s 410 – 410 not 400?” I queried. “Check that again.” I hesitated filling Fullerton’s request as I had set the AGS Orbit Insertion Routine soon after DOI-2.

“That’s affirmative – four one zero.

“Thank you, Gordy.” It is possible that, in my concern over Cernan foregoing the P63 Algorithm Test, the 410 +00000 did not get completely entered into the DEDA. This procedure was the Timeline a step before the scheduled Algorithm Test. Nothing in the transcript of the on-board tape recording (DSEA, Data Storage Electronics Assembly) specifically indicates an entry of 410 to +00000; however, it is clearly part of the post-DOI-2 checklist related to updating the AGS after the burn all of which were called out as completed.

“You better go back and check [Address] 400, now,” Cernan said.

“It’s okay. I fixed it [earlier].” Also, we had just confirmed the 400 had been set properly and that the AGS could control Challenger’s guidance.

“Okay,” Cernan agreed, and then, looking out the window, exclaimed, “Oh, man, are we down among them [mountains], Babe! Whooh!”

Challenger, Houston. I have a PDI TIG (Time of Ignition) update. It’s 112:49:51.87.” The previous time was about one and a half seconds later, suggesting that our perilune was lower than expected at this point. These uncertainties came from both the margins of error in various maneuvers and in un-modeled perturbations to our orbit caused by irregularities in the lunar gravitational field. “And NOUN 61 Cross-range,” Fullerton continued, “should be a plus 2.8. Over.”

“Okay,” I replied. “Say the seconds again on the PDI.”

“PDI seconds are 51.87. Over.”

“Okay. And the Cross-Range?”

“Cross-Range is a plus 2.8. Over.”

“Okay, Gordy,” I noted, “that time checks with our time out of P63.” This confirmed that the Powered Descent data load and state vector update we had been given a few minutes earlier matched that being carried by Mission Control.

“The LANDING RADAR breaker’s IN,” Cernan reported, “[and] I’ve got Altitude, Velocity [and] Power [indications]. We’re coming up on 4 minutes [to PDI].” He already had taken care of placing PINGS and AGS MODE CONTROL switches to AUTO, resetting the Digital Event timer to match the new PDI ignition time, and checking that the eight ball attitudes agreed with the PINGS NOUN 18 Roll, Pitch and Yaw of 000, 108 and 290, respectively.

“I’ll give you the final trim at 4 [minutes],” Cernan continued.

“Okay,” I said, watching each step carefully.

Challenger, Houston. You are GO for PDI.”

“Oh, thank you, Gordo. We are GO up here for PDI. …Doing the final trim at 4 [minutes].” With that, Cernan PROCEEDed on the NOUN 18 display or PDI attitude.

“Hello, America,” Cernan called. “Do you read Challenger? Hey, Jack, you can check your watch?”

“Okay.” My stopwatch would be a third backup Powered Descent timer.

“At 2 minutes, I’ll get the MASTER ARM [switch to ON].”

“All right.”

The first display in P63, NOUN 61, gave us the time in minutes and seconds from Ignition. Cernan set the Event Timer to this time. Entering NOUN 33 then gave us the Time of Ignition (TIG) for verification with Fullerton’s PDI time of 112:49:52.35. This would be about 47 minutes after DOI-2. He verified that GUIDANCE CONTROL was still in PINGS and put PINGS MODE CONTROL back to AUTO so that the computer would be in control.

With a KEY RELEASE and a PROCEED, NOUN 18 appeared and showed that the PINGS trimmed our attitude to 002 roll, 108 pitch, and 290 yaw, that is, an attitude on our backs and yawed toward the Earth for optimum S-Band communications. Cernan hit PROCEED, and we made a final trim maneuver to this attitude. To make sure the DAP was properly set, Cernan put the PINGS in idle (P00), entered VERB 48, and set the Digital Auto Pilot (DAP) for DESCENT – 4 JET – 20º/sec SCALE – 1º ATTITUDE DEADBAND – 2º/sec ATTITUDE RATE and BYPASS for both the Auto Throttle Check and the monitoring of Abort Push Button. A PROCEED set the DAP and a VERB 34 terminated VERB 48 activity. Then, he re-entered P63.

Powered Descent and Landing

Fig. 8.34. Illustration of the final stages of landing. The America CSM orbit was “circularized” to 70.0 x 54.7 nm over the horizon, expecting the lunar gravity perturbations to modify this to a circular 60 nm orbit before rendezvous with Challenger, three days later. Hi-Gate is pitchover of the LM and start of the approach phase. Lo-Gate marks final approach where the CDR can assume manual control of the LM. (Drawing modified from one in the NASA History Office Document Management System (DMS)).

Four days and ten minutes after leaving Kennedy Space Center, I told Cernan, “Okay. Coming up on two minutes to PDI; I’m changing over here [to the PDI Cue Card].”

“Okay,” replied Fullerton.

“Master Arm, On. Two minutes [to go until ignition]”.

“Okay, Houston. Two minutes. Master Arm is ON. I’ve got two good lights [for abort separation].” Cernan refers to the two redundant logic systems that would fire various explosive separation devices if we were to command an Abort Stage on the Ascent Stage engine.


“MODE SELECT is PINGS,” I confirmed.

“Okay. Once again,” Cernan reviewed the steps listed on the PDI cue card, “in average G, I’ll get the Engine Arm [switch]. You confirm the ullage, I’ll get the PRO [on the DISKEY]. I’ll back up the ullage [with minus x thrusters] and get the START [button at time of ignition].”

“Roger,” I said, as I understood what we would do at PDI.

“AUTO, AUTO, MIN,” Cernan called out as he confirmed the switch settings for MODE CONTROL for the PINGS and AGS and that his Throttle Control was at MINIMUM.

Challenger,” Fullerton called, “we’re going to leave Batt[ery] 3, OFF…until after ignition. We’ll call you.” This request reflected the previous discussion we had had about the half-volt difference between Batteries 3 and 4 and the need to condition the Ascent Batteries.

Roger. Yeah, I should have put that ON like we talked about.” I meant to say “put that OFF”.

“Man, I’ll tell you, we are getting close,” commented Cernan as he looked at the mountains to the east of the valley of Taurus-Littrow. At this point, we were flying on our backs, with Challenger’s ±z-axis pointed behind us and our feet pointed forward with our bodies aligned with our orbital path toward the valley. The 70-degree left yaw, however, gave Cernan a close view of the mountains and valleys over which we flew.

“Looking out your window is really strange, heh, heh…from over here.” I chuckled at the strange perspective that came from seeing the surface of the Moon go by Cernan’s window while flying over it feet first.

“One minute, Houston, and we’re standing by. We’re GO for PDI.”

“Roger. You’re looking good here.”

“Okay, approaching 30 seconds,” I noted, and then said, “Blank DSKY.”

“DISKEY blank,” confirmed Cernan.

“[There’s] average g,” I reported, “Got two [Descent Engine Caution] lights.”

[Average g referred to a computer routine in the PINGS that now would continuously average changes in velocity and lunar gravitational acceleration to solve its software’s equations of motion and update our guidance systems knowledge of where we were and how fast and in what direction we were moving over time (state vector).[40] The expected Caution lights for DESCENT GIMBLE and DESCENT REGULATOR were from sensors that showed that the gimble for the Descent Engine nozzle had not yet moved to its PINGS commanded position and that the Engine Propellant Pressure Regulators had not yet sensed propellant flow.]

“Okay, ENGINE ARM is DESCENT,” Cernan stated. “I think the tape meter drove. I’m not sure.” Here, Cernan refers to the Range Rate/Altitude Rate tape meter that would move slightly when the RCS thrusters provided 7.5 seconds of deceleration (ullage) to settle the fuel and oxidizer in their tanks prior to ignition. This, however, was a little ahead of the actual thruster firing. “[Jack,] Confirm the ullage.”

“Standing by for ullage…,” I replied, again referring to the automatic firing of the four minus z RCS thrusters, the deceleration from which would settle propellants in their tanks. “Ten seconds. …Fuel ullage. We’ve got ullage. …PROCEED on 99. It took. 2, 1, 0…” A flashing 99 on the DISKEY was the computer asking if we wanted to ENABLE the ENGINE ON command. Hitting PROCEED said “yes”, continue with automatic DECENT ENGINE ignition. Cernan was ready for a manual IGNITION if the computer did not supply that command to the engine.

“Ignition!, I called.

“Ignition, Houston,” repeated Cernan. “Attitude looks good. ENGINE OVERRIDE is ON, MASTER ARM is OFF. We got DESCENT QUANTITY LIGHT ON at ignition, [maybe] just prior to ignition.” This light normally would have indicated inadequate fuel; however, the properly functioning DESCENT ENGINE beneath us suggested either incomplete settling of the fuel or oxidizer at ignition (ullage) or a transient on the quantity sensor.

“DP tanks good. RCS is good at 15 seconds,” I called out, cross-checking the read-outs on the quantity gages for the Descent Propellant (DP) as well as the RCS.

“Roger,” acknowledged Fullerton.

“RCS is golden,” I continued. “Should be stable throttle up.” The PINGS held initial thrust at about 10% for 26 seconds, allowing the DESCENT ENGINE’s nozzle gimble to adjust the rocket’s orientation so that it was thrusting directly through Challenger’s center of gravity. This low thrust period also allowed LM CONTROL in Houston to look at telemetry and evaluate the engine’s performance prior to going to full power for the next nine minutes.

“Stand by,” I stated. “There’s…throttle up!”

“Throttle-up’s on time, Houston,” added Cernan. “And the computer likes it.”

[The PINGS’ display and entry keyboard (DISKEY) hung from the front panel just above the front hatch. Although we both could operate the PINGS, Cernan and I had agreed early in our training that good operational discipline during this critical phase of the mission required that he would make most of the entries on the DISKEY while I would monitor those entries relative to the checklist. This would avoid problems like he and Tom Stafford experienced on Apollo 10 when they lost track of what each other had done with the AGS MODE CONTROL switch.[41] The primary exception to this separation of duties would occur during the last phases of landing when Cernan would be occupied looking outside, and I would be calling out altitude and velocity information as well as changing the operational programs within the PINGS as landing events required. Prior to this, I would divide my attention between monitoring the PINGS and checking the information being supplied by the less accurate, but still very good, accelerometers and computer of the Abort Guidance System (AGS) to make sure there were no significant disagreements between the two systems. ]

“Roger,” replied Fullerton, implying without saying so that Mission Control agreed that throttle-up looked good to Thorson and Legler down at the LM CONTROL console.

“Still got the DESCENT QUANTITY LIGHT ON,” Cernan said. This suggested that the previous indication, indeed, showed a sensor problem. “Okay, attitude looks good, Jack.”

“Okay. At 30 seconds [after ignition], …[we] should have about 108 [degrees of pitch,” I continued. This pitch attitude, as we flew feet forward and on our backs, related to a pitch of zero if we were on level ground at the surface and included the 18 degrees of longitude east of Taurus-Littrow where we initiated our descent; that is, 90 plus 18 equals 108 degrees pitch.

“Oh, boy!” exclaimed an excited Cernan.

“AGS and PGNS are close [in altitude and velocity],” I reported, as I continued my scan of the two computer displays as well as those gages that showed how the DESCENT ENGINE and RCS were performing. I could only glance quickly out the window at the nearby mountains on rare instances.

“Okay, coming up on 1 minute.”

“One minute,” I confirmed. “You ought to have 98 degrees of pitch. Okay, H-dot is high right now.” H-dot was the mathematical term for our rate of descent (time derivative of altitude) and was high at this point because the computer thought we were above the planned trajectory to the landing site.

“Mark it, 1 minute.”

“Altitude’s high,” I reported.

Challenger, Houston. I have a NOUN 69 of plus 03400, plus 3400 feet [downrange]. Over.” NOUN 69 in the PINGS provided an entry register for us to take out up or down range errors in our projected landing point based on Doppler tracking from Earth. This capability originated from the major effort to develop pinpoint landings after Apollo 11. In this case, Doppler tracking showed we would land 3400 feet short so Fullerton was asking for us to enter plus 03400 in NOUN 69. Cernan added the correction, initially putting in an extra zero, but correcting the entry, quickly. I, again, verified the keystrokes and that they were in the first register of the DISKEY. Then, before hitting ENTER, Cernan waited while Mission Control verified that the PINGS had the right numbers. A bad correction could ruin your day.

“You’re looking at it,” he said.

“Okay; 3400. I confirm,” I added.

Challenger, you’re GO for ENTER.”

“Roger. GO for ENTER,” Cernan replied and then reported, “1:30. We’re GO coming through 57K [altitude].”

“Okay,” I said calmly, as I began my scan routine, again. “The altitude’s high and the H-dot is high. At least…that’s right. …Okay, at one…[rather] at 2 minutes [coming up], you ought to have 89 [degrees pitch] on the ball.” Because of its spherical shape, pilots often referred to the Attitude Indicator as the “ball” or sometimes by the pool table term, “eight ball,” as it also was black with white symbols.

“We’re still 30 feet per second high in H-dot. But we’re about 8000 feet high…” I continued, “[make that] 7000 [feet].”

Challenger, Houston, we’d like you to cycle the PQGS (Propellant Quantity Gauging System) switch OFF and then back ON.” Fullerton should have said the PQGS “circuit breaker”. LM CONTROL may have over simplified their message to him, but I knew what he meant.

“Okay, Houston. Coming up on 2 minutes.”

I replied to Fullerton with, “Okay. It’s (meaning the circuit breaker) OFF. And it’s back ON. Quantity Light is out.

“Roger. That should be good now.”

“And, Houston,” Cernan started as Fullerton was talking, “we…Okay. We have Engine Thrust and Commanded Thrust, full-scale high.”


“Man, that looks good,” I remarked, admiring the work of the Descent Engine.

“Okay, babe, let’s check them at 02:30.”

“RCS looks good…[and] Cabin [pressure] looks great,” I answered.

“02:30, I’m about 89 degrees [pitch],” Cernan observed, “…coming through 51.5 thousand feet.”

“89 is great,” I confirmed from the PDI Cue Card. “We’re catching up on our altitude. We should start dropping H-dot here a little bit. AGS and PGNS are together. AGS has us a little bit out of plane. …[It] has us north of track.” If a real out of plane error and not just drift in the AGS, this might become a problem, as the planned landing point lay closer to the north wall of the valley than the south.

“Okay, Gordo; coming up on 3 minutes, we’re GO, and…we’re out of 49K [feet],” Cernan called.

Challenger, Houston, …you’re GO at 3.

“Roger. Understand we’re GO.”

“Okay. At 3 minutes, 82’s your ball number,” I continued. “We’re still looking for the right altitude, so H-dot is high.”

“Okay…” Cernan responded. “The day of reckoning comes at 4 minutes, Jack. …Got the weight (deceleration g’s) building up, looking good. Attitudes are good.”

“Okay, at 03:30, you ought to have 79 [on the ball]…”

“Okay, it’s right on,” Cernan replied.

“We’re still a little high,” I repeated, “about 2500 feet [high]. H-dot is still high.” This error relative to plan had now changed from 7000 feet to 2500 feet at a descent rate of about 40 feet per second.

“Okay. The tape meter [for the Landing Radar data] moves in spurts and jerks, both on altitude and altitude rate,” observed Cernan. Apparently, the Landing Radar had begun to get some returns from the lunar surface; however, we would not use that to update the guidance system on altitude and velocities until it was clear the data was good.


Challenger, Houston. You’re Go at 4 minutes.”

“ED BATs are 37.2 [volts],” I reported, moving the battery voltage indicator switch to various positions. ED referred to the batteries that supplied power to the Explosive Devices, or pyrotechnic cutters that would separate the Challenger’s Ascent and Descent Stages in case of an Abort Stage command.

“Roger. ED BATs.”

“Okay, Gordo, yaw’s coming at 3:40.”

“Roger,” responded Fullerton. The yaw of the Challenger, that is, its rotation around the Descent Engine thrust axis, partially controlled the pointing of the steerable S-BAND Antenna. We had begun Powered Descent with 70 degrees left (south) yaw to optimize communications, as we were about 20 degrees north of the Moon’s equator and the plane that included the Moon’s orbit around the Earth. Now, to optimize the pointing of the Landing Radar, but still have plenty of margin for communications, we reduced that yaw to 20 degrees left.

“And the radar lights are out! called Cernan. “Beautiful!” Cernan meant the single light above the tape meter showing altitude and altitude rate.

“Okay, sounds great,” agreed Fullerton. “Both Nav[igation] systems (PINGS and AGS) are GO. …Right on the line.” Fullerton’s use of the word “line” suggested that he was looking at the big projected graphics in the front of the Mission Operations Control Room (MOCR) where a Lunar Module icon moved along a line showing the planned trajectory.

“You’re looking at Delta-H,” Cernan told Mission Control as he called up a display of NOUN 63 that showed the difference between the altitude extrapolated by the PINGS and that being sensed by the Landing Radar.

“And you’re GO for a VERB 57.”

“Okay, Verb 57 is in.” Cernan’s entry of this Verb allowed the radar data to be used by the PINGS calculation of our current altitude and velocities.

“Hey, Houston,” I asked, “is the AGS [indication of] out-of-plane correct?”

“Stand by.”

“Okay,” continued Cernan, “coming up on 5 minutes, Jack. Let’s take a check at it. About 74 degrees [of pitch].”

“That’s good. 70 feet per second [descent rate]; we’re coming down. 36.8K [altitude]. …You’re still [two or three] thousand feet high.”

Challenger, you’re GO at 5 minutes…”

“Okay, Houston; we’re now out of…”

“…the AGS out-of-plane looks okay to us,” Fullerton interrupted. What I wanted to know was, is the indication real or not. I decided not to worry about it anymore. If we were dangerously out of plane or if the AGS guidance was deteriorating, Mission Control would tell us.

“Okay,” acknowledged Cernan. “Go at 5 [minutes]. We’re out of 36.5 [thousand feet] now. We’ve got the Earth right out the front window.” With Taurus-Littrow much farther north that other Apollo landings, except for Apollo 15, Cernan had a great view of the Earth to the southwest all through Powered Descent. Unless I leaned in very close to the right hand window, my view was blocked by the front, nose-like structure of the Challenger.

Challenger, Houston. Battery 3, ON, at your convenience.”

“Battery 3 is [now] ON,” I said.

“05:30, Gordo,” Cernan called. “We’re Go. We’re out of 34K.”

“73 [degrees pitch], 34 [thousand feet altitude]. We’re right on altitude. The H-dot ought to start dropping off. Except that we want to keep it high.”

Unable to resist acting as “the Commander”, Cernan said, “You’re allowed two quick looks out the window, one now and one when we pitch over.”

“I can’t see a thing except the Earth,” I replied. Even the 20 degrees of yaw had me still looking generally above the north horizon of the Moon.”

“That’s what I’m telling you to look at!”

Laughing and pretending to be the startled rookie: “Oh! There’s the old Earth!”

[Cernan commented years later[42] that, “Jack couldn’t spend much time looking out the window. He went through the whole landing and hardly had a chance to see where we were going, because he was looking at fuel and oxidizer gages, looking at battery currents, updating the AGS guidance, verifying my entries in the PGNS, and writing things down. So he was very busy inside the cockpit and probably stole a glance or two outside. I had to look outside. …But poor Jack had to keep his head buried in the cockpit.” This candor on Cernan’s part was much appreciated; however, on later occasions he claimed many times that he did not need my help to land the Challenger. The design of the Lunar Module assumed that two pilots would share the duties of flying. Having the Commander look back and forth between the window and the Landing Point Designator (LPD) grid etched into it and the displays and instruments in the cabin would have been made to order to induce vertigo as well as reducing his concentration on actually landing. This need for pilot interaction is particularly clear in the period between pitch over and landing (see below).]

“Okay, Houston, coming up on 6 minutes.”

“[At] six minutes, you ought to have 72 on your ball,” I noted.

Challenger, you’re GO at 6 [minutes].”

“72 [degrees] and Go,” Cernan said, acknowledging both Fullerton and me. At this point, Challenger was about 40 miles from the landing site.

Continuing my monitoring, I reviewed the trajectory status against the Cue Card profile: “31 (thousand feet). Altitude’s great. H-dot’s great. AGS and PGNS are very close, couple feet per second [descent rate] difference.”

“Okay, Houston,” Cernan called. “As we went over the hump, Delta-H (altitude difference) just jumped.”

“Roger,” said Fullerton, noting the fact that we had just flown over the mountains (“hump” in Fig. 8.35) at the eastern end of the valley of Taurus Littrow. This resulted in a temporary disagreement between the PINGS calculation of our altitude relative to the landing site and the Landing Radar’s raw data that had just seen an increase in altitude of a couple of thousand feet. We expected to see this as confirmation that both guidance and radar were functioning properly.

Fig. 8.35. The ground track of the flight trajectory of Challenger into the valley of Taurus-Littrow coming from the right. The tip of the red arrowhead is pointing just short of a very small crater called Rudolph which is very close to the landing site. At the east end of the valley, Challenger flew over a mountainous area labeled the “hump” where Delta-H between the PNGS calculated model altitude of Challenger and the landing radar actual altitude differed as was expected. The Earth could be seen in the direction above the South Massif. (Base photo NASA AS17-M-0595).

Two seconds later, Cernan reported, “And looks like it’s [DELTA-H] back down,” meaning that the computer had incorporated the data from the Landing Radar.

“Roger. Sounds good,” Fullerton replied.

“6:30, Geno,” I reported.

“It looks good, babe.”

“72 (degrees pitch). Altitude is right on [plan]. H-dot is very close [to plan].

“Okay, 30K, yaw to zero,” Cernan read from the Cue Card. This rotation finally put the windows looking directly along our trajectory to the landing site and gave me a chance for a quick look at the North Massif and its western reaches. (see the trajectory path into the valley in Fig. 8.35 above)

“Throttle down time (will be) 7 plus 26,” updated Fullerton, based on the MOCR’s estimate of how the PINGS calculations were coming out.

“7 plus 26,” I repeated. At this point, the Descent Propulsion System had cut our orbital speed from about 5500 feet per second to about 1000. This remaining velocity would be taken out at reduced thrust. Also, when we pitched forward to view the landing area, the effective thrust would be reduced further as our x-axis would be oriented at an angle to the actual trajectory.

“Okay, we got everything?” Cernan asked. “We’re yaw at zero.”

“…At 7 minutes, 67’s your [pitch] angle. 26, …[rather] 27 [fps H-dot]; that’s great…” I continued my cross-check with the Cue Card.

Challenger, you’re GO at 7.”

“…H-dot’s slightly high, but okay,” I reported.

“Okay, Gordo. We’re Go at 7, we’re now out of 25,000 feet.

Again looking at the AGS, I updated Cernan: “We’re quite a bit out of the Command Module [orbital] plane, but I guess we’re on target [for the landing site].” This out of plane, if real, would increase the energy necessary to reach America in case of an Abort, but would be well within the capability of the Ascent Engine.

“Okay, watch the throttle, now. Here it comes.”

“Throttle down!,” we reported, simultaneously.

“…at 27 [seconds]; computer likes it!” recorded Cernan.

“Beautiful,” I said, obviously still appreciative of the performance of the Challenger.

“Roger,” replied Fullerton, sounding somewhat less impressed or distracted by other activities in the MOCR.

“Okay, 07:30, 63 [degrees pitch].”

“Okay, 1:45 to pitch over, Jack.”

“Okay, 63’s your angle,” I repeated.

“About 56 now,” Cernan said.

“Okay, that’s getting closer.” This six degrees less pitch meant that the PINGS had flattened its trajectory to the landing site, possibly calculating that it had taken out the down range error Mission Control had measured.

“H-dot and H [altitude rate and altitude] are great. …Standing by for the [Sequence] Camera,” I reported. This sixteen-millimeter Mauer camera would film the landing at 12 frames per second. It was mounted in the window in front of the LMP position and one of my many jobs was to remember to turn it on after Pitch-Over.[43]

“19K, Houston. We’re GO coming up on 8 (minutes),” called Cernan.

“Okay. The old camera’s on, Gordy. Believe it or not.”

“How about that,” said Fullerton. Obviously, I had missed turning on the Sequence Camera in one or more Mission Simulations. “You’re GO at 8. Monitor fuel, 2.” This last call referred to Mission Control’s judgment from telemetry as to which fuel gage would give us the best onboard quantity information.

“Fuel 2: [is reading] 27 [percent]. That’s good,” I acknowledged, referring to the Cue Card data.

“Come on, baby!” Cernan urged.

“Okay, at 08:30, Geno,” I added more calmly.

“Okay, I got (see) the South Massif.” At a pitch angle of 60 degrees and an altitude of 16,000 feet, Cernan could just see the top of this 7000 foot high Massif that formed part of the south wall of the valley of Taurus-Littrow.

“Okay, update the AGS [altitude], Houston? Yes?” I asked.

“That’s affirmative; update the AGS.”

Okay, Gordo,” Cernan persisted. “I’ve got Nansen; I’ve got Lara; and I’ve got the Scarp. Oh, man, we’re level with the top of the Massifs, now.”


Cernan, by leaning close to his window, could now see several of the named features (see Appendix 3) to the west of the landing site, now five miles ahead and 15,000 feet below us. My quick glance out the right window also gave me the impression of being level with the top of the 6-7000 feet high North Massif possibly due to the lunar horizon being much closer than we experience in flying over the Earth.

Fig. 8.36. An important aspect of simulator training for the LM crews was to be able to see the landing site area as it would appear when they were actually landing on the Moon. Since digital photogrammetric modeling of the actual lunar surface was more than 50 years into the future, the problem was solved in the 1960’s by using a TV camera moving below a giant plaster model constructed of the landing site and placed upside down in the simulator. The above photo shows the landing site model for Apollo 15, the only one that survived later “non-useful” equipment purges of NASA. It is just being delivered at NASA’s Landing and Ascent facility on 29 April 1971. Further descriptions of these photos provided by Paul Fjeld are given in the ALSJ. (NASA photo 108-KSC-71P-290).

Fig. 8.37. The model in the receiving area. Here names of several craters have been added to the photograph. The hundreds of hours that went into the construction of this model are evident. (NASA photo 108-KSC-71P-293).

Fig. 8.38. The model in place is mounted upside down near the ceiling. Below, behind screens and not visible in this view, a TV camera and a bank of kleg lights to simulate shadowing can be commanded via computer to move along the model in response to the simulated path being commanded by the PINGS, AGS or Commander. (NASA photo 108-KSC-71P-291).

Fig. 8.39. (Top): The result seen in the simulator LM window at 5000 ft. on approach to the landing site. (Bottom): Same as the top view with several craters identified. Apollo 15’s Falcon LM landed on the northwest rim of the smaller of the two ‘Last’ craters marked at right.  (NASA/ALSJ/Markus Mehring).

“Okay. …[00]151, entered.” I loaded this new altitude reference in DEDA Address 223 as P64 displayed 15,100 feet altitude that incorporated the Landing Radar measurements. The AGS now knew our altitude within ± 100 feet. As discussed earlier, I worked with the engineers of TRW to develop this technique for an altitude update in the AGS.

“Okay, Jack, …Pitch-Over is at nine [minutes] 24 [seconds]; 24 on the Pitch-Over,” Fullerton informed us.

Challenger. You’re Go at 9 (minutes).”

“Okay, Gordo, we’re out of 11,000 [feet] at 9.”

“Okay, stand by for Pitch-Over,” I called.

“Oh, are we coming in. Oh, baby!”

“Okay; through 9000.” On tapes of the landing conversation, I sound much calmer than Cernan; but then my job was contained within the cabin, and I did not have the continued stimulus from the dynamic visual scene Cernan experienced during the approach into a valley deeper than the Grand Canyon of the Colorado River.

“Stand by for Pitch-Over, Jack.”

“8000,” I read off the DISKEY.

“I’ll need the PRO[CEED after Pitch-Over].”

“I’ll give it to you.”


There it is! PROCEEDed!” Hitting the PROCEED button on the DISKEY told the PINGS to go into P66, the landing program, from P64, the powered descent program. Cernan made the decision to change programs as soon as he had a full view of the landing area after the PINGS commanded Pitch-Over to a much more upright attitude. Pitch-Over actually took us from about 60 to 20 degrees pitch up, still allowing the Descent Engine thrust to continue to slow both our forward and vertical velocity.

“And there it is, Houston!” an even more excited Cernan called. “There’s Camelot (Crater)! Wow! Right on target.”

“Wow! I see it!” This used up my second look out the window and gave me a view of the ~600 meter diameter crater I had named Camelot, primarily in honor of President John F. Kennedy who gave us the challenge to beat the Russians to the Moon, a challenge that motivated everyone I knew during Apollo.

“We got them all.” Cernan was referring to the various named features, mostly craters near the planned landing point.

“42 degrees, …37 degrees through 5500. 38 degrees…,” I said as I began the callouts that would tell Cernan where the PINGS wanted to land with reference to the graduated vertical lines scribed on his window. This feature was termed the Landing Point Designator (LPD) and was graduated in “degrees” from 0 at the top to 90 at the bottom.

Fig. 8.40. (Left): The LPD scale in the CDR’s window seen from inside LM-9. Note that the vertical scale numbers (called out as “degrees”) increase downwards. LM-9 was originally scheduled to fly on Apollo 15 before that mission was given extended capabilities, including a longer stay time on the surface and the ability to carry the Lunar Rover. The extended mission LM-10 was assigned to Apollo 15, and LM-9 became a “hangar queen” at the Kennedy Space Center. As I recall, because of late test issues with the original landing and rendezvous radars on Challenger (LM-12), we actually flew with those radars from LM-9 as substitutes. (Right): The same scale seen from the exterior side of LM-9’s window. Explanation for the use of the double scale is given in text. (NASA/ALSJ /Randy Attwood).

[The LPD consisted of a combined hardware-software subsystem that provided an overall capability for a pilot controlled landing. In the landing program, P66, the PINGS supplied a number in degrees that correlated with two, superposed sets of vertical lines scribed on Cernan’s window. With his eye properly aligned so that the double set of scribed lines appeared as one, Cernan now could use the angles I gave him to see where the PINGS would land us along Challenger’s line of flight and along the merged vertical lines. On the other hand, if boulders or craters at this landing point appeared to be a problem, Cernan could tell the PINGS to re-designate that point left or right by pulsing his right hand controller left or right. Challenger would roll left or right to make the change. Similarly, he could re-designate down range or up range by pulsing the controller forward or back and Challenger would pitch forward or back, respectively. The absolute distance associated with each re-designation decreased as our altitude decreased. If, for some reason, the PINGS did not respond to Cernan’s hand controller inputs, he could have told me to pulse my controller to supply the re-designations.]

Challenger, you’re GO for landing.”

“5000 feet; 42 degrees [LPD angle]…through 4000; 47 now…47 degrees through 3500…49 degrees…3000 feet, 53 degrees.” The increase in LPD numbers indicated that with decreasing altitude the designated landing point was moving down in the window.

Fig. 8.41. A frame grab from the 16 mm DAC video of the landing. I had just said “…through 3500” at this point. In the distance are (West) Family Mountain at left; what looks like a snow-covered smaller mountain; and the even smaller (Old) Family Mountain to the right of the latter in the middle of the frame. (see discussion in the ALSJ for these names). The bright debris avalanche partially crossing the valley entrance is also plainly visible. The dark oval spot in the finger closest to the viewer is Shorty Crater, where I discovered the orange soil (see Chapter 11, Station 4 – Shorty Crater). The very large crater abutting the left edge of the window is the ~600 m diameter Camelot Crater. The bright spot above it is from backscattered sunlight (Lambertian reflectance) from the fine-grained particles in the regolith caused by the sun directly behind us (zero phase angle), and is independent of our view angle relative to the surface. (Video provided by Ben Feist[44])

“Okay, I’ve got Barjea (Cernan pronounces it ‘Bar-Hay’ as can be heard in the video link below); I’ve got Poppie; I’ve got the Triangle,” Cernan said with continued excitement. These features are craters, and in the case of Triangle, a group of three craters, in the vicinity of the planned landing point. Meanwhile, I continued a steady callout of altitudes, LPD angles, and rate of descent.

“At 2500 feet, 52 degrees. …H-dot (rate of descent) is good. At 2000, H-dot is good. Fuel is good. …1500 feet, 54 degrees, Gene. …Approaching a thousand [feet]. …Approaching a thousand feet. …57 degrees. Okay, you’re through a thousand, and I’m taking…Radar altitude [tape meter] and PINGS altitudes agree. …You’re through 800 feet. H-dot’s a little high.”

“Okay; I don’t need the [LPD angle] numbers anymore,” Cernan said, as now the challenge he faced was to just find a crater and rock free spot to land. All he needed to pay attention to now were my call outs of his rate of descent and any lateral rates that might creep in.

“Okay, you’re 31 feet per second, going down through 500… 25 feet per second through 400. That’s a little high, Geno.” Actually this descent rate was a lot higher than the normal profile we had trained to fly. It should have been about 16 feet per second at this point. Cernan, however, apparently felt that he could slow the descent rate quickly.[45]


“300 feet, 15 feet per second. A little high. … H-dot’s a little high,” I warned, raising my voice a bit. The descent rate should have been about 9 feet per second at 300 feet.

“Okay. I’ve got P66.” In P66, Cernan now has “manual” control of the landing by using his right hand controller to command changes in engine nozzle orientation and thereby altering Challenger’s flight path. He had already had control of the Descent Engine’s thrust level through his left hand controller, or T-handle. Here is where the LLTV training for Commanders pays off.[46]

“Okay. …9 feet per second down at 200 [feet altitude]. Going down at 5. Going down at 5. Going down at 10 [feet per second]! … Cut the H-dot!” This was the only time I really raised the emphasis in my voice to something like a command. After the mission, Thorson and Legler, who had been manning the LM CONTROL console, thanked me for making this clearly evident to Cernan.

Fig. 8.42. Frame grab from the DAC at 200 ft. The shadow of Challenger with its landing struts deployed is clearly seen emerging from the solar backscattered reflection, reminiscent of the phenomenon called the ‘Glory’ sometimes observed around aircraft shadows cast on lower lying clouds, forests, or fields. See Fig. 8.43 for other feature identifications.

Fig. 8.43. Labeled version of the previous figure. Rudolph is the ~50 m diameter crater at right. At left, 1,2,3 mark boulders and “c” marks 3 craters identified in the overhead LROC photo, Fig. 8.44 below. I placed the ALSEP just about halfway between boulders 2 and 3. The nearby Geophone Rock (Chapter 10) is outside the frame edge as marked.

Fig. 8.44. The boulders marked in Fig. 8.43 are also labeled 1,2,3 here. “c” marks the 3 craters immediately below the LM leg shadows in the previous photo. “G” is Geophone Rock but not visible in Fig. 8.43 (it was visible briefly in the DAC video at 1000 ft!). LM is the touchdown site and remaining descent stage of Challenger. Rudolph is at upper left, and Poppie is at lower right. Rover tracks can still be seen at the site. The small dark smudge halfway between boulders 2 and 3 is where I emplaced the ALSEP experiments. (Base photo from the LROC Apollo 17 landing site page).

I then continued, “The fuel’s good. 110 feet. …Stand by for some dust. [You need a] little forward [velocity], Gene.” Cernan rightly wanted a little forward velocity so that he would be touching down on surface he had already seen go beneath the vehicle. Unfortunately, the view out of Challenger’s window made it difficult to judge velocity across the lunar surface, so the Landing Radar provided the best such information.

Moving forward a little. 90 feet. Little forward velocity. 80 feet; going down at 3. …Getting a little dust.” I had taken a couple of quick glances out my window and saw dust begin to stream away from Challenger’s Descent Engine nozzle. “We’re at 60 feet; going down about 2. Very little dust. Very little dust. …40 feet, going down at 3.” Small surface rocks, still in sunlight, showed through the streaming dust curtain.

Stand by for touchdown,” Cernan called.

Fig. 8.45. At 20 ft to touchdown, the shadows of the 6 ft (2 m) sensor probes sticking out from beneath the footpads are visible along with some dust obscuring small craters and boulders at the bottom of the frame.

Fig. 8.46. At 10 ft, there is more dust. The sensor probes are about to touch the surface. When that happens, the blue contact lights (Fig. 8.47) on panels 1 and 3 will turn on. The engine is immediately shut down by our hitting the Engine Stop button. We freefall the remaining distance to the surface. In watching the video of the landing linked below, note that the picture is still fuzzy from the dust entrained before contact. Within 7 or 8 seconds after contact, the picture becomes clear as the engine effluents tail off—a measure of how fast the dust and effluents leave the area along ballistic paths in absence of any atmosphere.

“Stand by,” I repeated, watching in my peripheral vision for illumination of the blue CONTACT LIGHT up and to the right of the DISKEY. “25 feet, down at 2. Fuel’s good. 20 feet…going down at 2. 10 feet. 10 feet…


Fig. 8.47. Cernan’s contact light is marked by the white arrow in the upper middle of panel 1. My eyes were glued on the one marked at lower right on panel 3. (Base photo NASA/ALSJ/Paul Fjeld).

(A 5 min 9 sec view of the 16 mm DAC video supplied by Ben Feist of the landing sequence from 10 miles from the landing site to just after touchdown can be seen here in a separate window[47]. It is a 95 Mb file if the reader wishes to download it.)


(to be continued….)


    1. In the quoted dialog and annotation directly related to the Apollo Seventeen Mission, black = normal mission activity and commentary, red = spacecraft anomaly discussions, blue = Earth observations, brown = Lunar Module Challenger discussions, green = Public Affairs Office transcripts or news updates from Mission Control, purple = lunar observations, italics = onboard recorder transcripts (Data Storage Equipment or Command Module DSE and Data Storage Electronics Assembly or Lunar Module DSEA), and turquois font = probable dialog derived from the author’s memory.

      In addition, parentheses (-) in the text are used to clarify the meaning of a preceding word or phrase. The use of text inside brackets [-] provides completion of an untranscribed word of phrase. Brackets [-] enclosing letters or words quoted from a checklist complete abbreviated words to clarify what the word in question means. Also, double-indented paragraphs that set off explanatory details are enclosed in brackets.

      The LGC (Lunar Module Guidance Computer) commands are referred to occasionally in text as Pxx (Program i.d. number), Nounxx (data specification), or Verbxx (action number) to be carried out by the LGC when entered by hand.

    2. Frame grabs by the Editor were taken from the video sequence of the landing prepared for this Chapter by Ben Feist. A complete computer archival display of all aspects of the mission, including videos, photos, collected samples, recordings of the transmissions, etc. can be found at

    3. The author benefited greatly from the Apollo Lunar Surface Journal (ALSJ) and the initiative of Dr. Eric Jones to bring mission crews together to work through the transcripts and audio and video tapes in order to insure the accuracy of the dialogue and to determine exactly who said what. With only one exception, the Lunar Module crews that went to the Moon responded positively to my request that they help Dr. Jones in his effort to create the Journal. The Journal’s edited transcripts were particularly useful for Apollo 17 as Gene Cernan’s and the author’s voices were similar enough at times to confuse the transcribers of the audio tapes.

    4. Also available on Youtube at as provided by “pecvillian”.

    5. Also available on YouTube at as provided by “WillieNelson”.

    6. Also available on YouTube at as provided by “tuxthemagicpenguin”.

    7. Also available on YouTube at as provided by “billbilladaadaa a”.

    8. Mendell, W. W., and F. J. Low, 1974, Preliminary results of the Apollo 17 Infrared Scanning Radiometer, The Moon, 9, 1-2, pp. 97-103.

    9. McCauley, J., 1983, Orientale Basin, in Wilhelm’s, D. E., The Geological History of the Moon, USGS Professional Paper 1348.

    10. Color Codes for the Apollo Flight Director teams: (1) Chris Kraft – Red; (2) Gene Kranz – White; (3) John Hodge – Blue; (4) Glynn Lunney – Black; (5) Cliff Charlesworth – Green; (6) Pete Frank – Orange; (7) Milt Windler – Maroon; (8) Gerry Griffin – Gold.

    11. Kelly, T. J., 2001, Moon Lander, Smithsonian Institution Press, Washington, p. 34-84; Low, G. M., 1975, The Spaceships, in E. M. Cortright, editor, Apollo Expeditions to the Moon, NASA SP-350, p. 59-66.

    12. Block II decision; Encyclopedia Astronautica, LM Descent Propulsion,

    13. Beattie, D. A., 2001, Taking Science to the Moon, Johns Hopkins, p. 230.

    14. See Chapter 1.

    15. See the Apollo 17, 1972, LM Activation Checklist (as flown), S/N 1003, p. 3-1 to 3-39.

    16. Readers interested in the names and dispensations of the 15 LMs built by Grumman should consult this link.

    17. Fjeld, P., 2012, ALSJ. Users might wish to consult the higher resolution images on this ALSJ page in order to make the various dials and switches of instrument panel photos more readable.

    18. Grumman Corp., Apollo News Reference Lunar Module Quick Reference Data, available from the ALSJ. A large scale schematic drawing of the instrument panels of LM-06, Intrepid of Apollo 12, is available here. It provides an excellent adjunct to the photos of the LM-12 instrument panels in this chapter provided by the previous reference.

    19. Kelly, T. J., 2001, Moon Lander, Smithsonian Institution Press, Washington, p. 83-84, 120, 138-140; Campos, A. B., 1972, Apollo Experience Report Lunar Module Electrical Power Subsystem, NASA Technical Note, NASA TN E-6972, 14 p.; also see the developmental timelines in the Encyclopedia Astronautica,  LM Electrical.

    20. Kelly, T. J., 2001, Moon Lander, Smithsonian Institution Press, Washington, p. 43-44, 120-121. Gillen, R. J., et al., 1972, Apollo Experience Report – Lunar Module Environmental Control Subsystem, NASA Technical Note, NASA TN D-6724, 44p.; also see the developmental timelines in the Encyclopedia Astronautica, LM ECS.

    21. Kelly, T. J., 2001, Moon Lander, Smithsonian Institution Press, Washington, p. 63-64.

    22. Mindell, D. A., 2008, Digital Apollo, The MIT Press, Cambridge, p. 102-108.

    23. See Chapter 1.

    24. Mindell, D. A., 2008, Digital Apollo, The MIT Press, Cambridge, p. 139-142.

    25. Dietz, R. H., et al., 1972, Apollo Experience Report – Lunar Module Communications System, NASA Technical Note, NASA TN D-6974, 60p.; Kelly, T. J., 2001, Moon Lander, Smithsonian Institution Press, Washington, p. 24, 43; also see the developmental timelines in the Encyclopedia Astronautica, 2012, LM Communications.

    26. Holley, M. D., et al., 1976, Apollo Experience Report – Guidance and Control Systems: Primary Guidance, Navigation, and Control System Development, NASA Technical Note, NASA TN D8227, p. 37-43; also see the developmental timelines in the Encyclopedia Astronautica, LM Guidance.

    27. Kelly, T. J., 2001, Moon Lander, Smithsonian Institution Press, Washington, p. 55-56; also see the developmental timelines in the Encyclopedia Astronautica, LM Descent Propulsion.

    28. Rozas, P., and A. R. Cunningham, Apollo Experience Report: Lunar Module Landing Radar and Rendezvous Radar, NASA Technical Note, TN D 6849, p. 6-7.

    29. Kelly, T. J., 2001, Moon Lander, Smithsonian Institution Press, Washington, p. 121; Rozas, P., and A. R. Cunningham, 1972, Apollo Experience Report – Lunar Module Landing Radar and Rendezvous Radar, NASA Technical Note, NASA TN D-6849, 31 p.; also see the developmental timelines in the Encyclopedia Astronautica, LM Guidance.

    30. The LM DAC undocking sequence was prepared for this chapter by Ben Feist. Users can either watch or download the file from the link in text (~102 Mb).

    31. Rozas, P., and A. R. Cunningham, 1972, Apollo Experience Report – Lunar Module Landing Radar and Rendezvous Radar, NASA Technical Note, NASA TN D-6849, p. 2-5; also see the developmental timelines in the Encyclopedia Astronautica, LM Guidance.

    32. Hammock, W. R., et al., 1973, Apollo Experience Report – Descent Propulsion System, NASA Technical Note, NASA TN D-7143, p. 31; also see the developmental timelines in the Encyclopedia Astronautica, LM Descent Propulsion.

    33. Hammock, W. R., et al., 1973, Apollo Experience Report – Descent Propulsion System, NASA Technical Note, NASA TN D-7143, p. 4-5.

    34. Marley, W. G., T. K. Wu, R. A. Harwood, 1971, LM AGS Operating Manual: Flight Program 8. TRW Contract NAS 9-8166, NASA 17618-H110-RO-00, p. 6-7.

    35. Kurten, P. M., 1975, Apollo Experience Report – Guidance and Control Systems” Lunar Module Abort Guidance System, NASA Technical Note, NASA TN D-7990, 66p.; also see the developmental timelines in the Encyclopedia Astronautica, LM Guidance.

    36. The LM DAC sequence pass over Taurus-Littrow was prepared for this chapter by Ben Feist. Users can read, view and listen to this part of the sequence in real time at

    37. Watters, T. R., et al. 2010, Evidence of recent thrust faulting on the Moon revealed by the Lunar Reconnaissance Orbiter Camera, Science, 329, p. 936-940.

    38. Flight Control Division, 1972, Final Mission Rules: Apollo 17 (AS-514/114/LM-12), Manned Spacecraft Center, September 1, p. 3-10 – 3-12. A copy of these rules as a 42 Mb PDF is available at the ALSJ.

    39. Slayton, D. K., 1994, DEKE! p. 232; Cernan, E., and D. Davis, 1999, The Last Man on the Moon, St. Martin’s Press, New York, p. 129-141, 217-218, 257-265; Stafford, T, 2002, We Have Capture, Smithsonian Institution Press, p. 149-150; Kraft, C. 2001, Flight, Dutton, New York, p. 347; Low, G. M., 1971, Personal notes #69, Archives and Special Collections, Folsom Library, Rensselaer Polytechnic Institute, Troy, NY, pp. 15-16.

    40. Jones, E. M., and P. Fjeld, AGC average g routine.

    41. See Chapter 2.

    42. See Jones, E. M., Apollo Lunar Surface Journal, Apollo 17, Landing at Taurus-Littrow, time hack 112:55:45.

    43. The Apollo 17 landing can be viewed and heard as part of the Lunar Landing display at the Smithsonian National Air and Space Museum in Washington, D.C. But a brief 5 min 09 sec clip of the DAC video I made of the landing is included in this chapter thanks to Ben Feist.

    44. Frame grabs by the Editor were taken from the video sequence of the landing prepared for this Chapter by Ben Feist. A complete computer archival display of all aspects of the mission, including videos, photos, collected samples, recordings of the transmissions, etc. can be found at

    45. See Jones, E. M., Apollo Lunar Surface Journal, Apollo 17, Landing at Taurus-Littrow, time hack 113:00:32.

    46. Unconventional, Contrary, and Ugly: The Lunar Landing Research Vehicle, 2005, Matranga, G. J., C. W. Ottinger, and C. R. Jarvis, Monographs in Aerospace History #35, NASA SP-2004-4535, 2005. Post-mission, Apollo landing Commanders Armstrong and Cernan affirmed that the LLTV experience was important to a successful outcome. Apollo 16 Commander John Young stated that good simulation would be sufficient (personal communication).

    47. Readers can also listen, watch, and read the landing from the statement: “stand by for pitch-over” on Ben Feist’s Apollo 17 website at


Copyright © by Harrison H. Schmitt, 2020. All rights reserved.