112:47:52 Cernan: Okay.
[They are making final preparations for the powered descent to the lunar surface.]112:47:54 Schmitt: Master Arm, On. Two minutes (to go until ignition).
112:47:58 Cernan: Okay, Houston. 2 minutes. Master Arm is On. I've got two good lights.
112:48:00 Fullerton: Roger.
[By turning on the Master Arm switch, they are enabling activation of explosive devices with which they will open the fuel valves in the Descent Stage and others which would allow them to discard the Descent Stage in the event that they have to abort the landing and use the ascent stage to return to orbit. "Two good lights" refers to redundant pair of circuits.]112:48:01 Schmitt: Mode Select is PGNS.
[David Woods has provided scans of pages 15 ( 1.0Mb ) and 16 ( 1.0Mb ) from the Apollo 15 Lunar Module Cue Cards, which cover various abort scenarios. On page 16, for a return to orbit using either the descent engine (lefthand column) or the ascent engine (righthand collumn), The Commander would check the position of the Guidance Switch and then push either the Abort button for a return to orbit using the descent engine or Abort Stage button for a return using the ascent engine.]
[The LM has two navigation systems: the Primary Guidance and Navigation System (PGNS), pronounced "pings", and the less capable Abort Guidance System (AGS), pronounced "ags" The AGS would only be used for guidance purposes in the event of a PGNS failure. In that case, mission rules call for an abort of the descent and a return to orbit. Under normal conditions, the AGS was used to double check the performance of the PGNS and, as Gene discusses below, it is an open question as to whether or not he would have aborted the landing in the final stages if the PGNS had failed and he was getting good AGS data.]112:48:03 Cernan: Okay. Once again, in average G, I'll get the Engine Arm (switch). You confirm the ullage, I'll get the Pro. I'll back up the ullage and get the Start.
[Gene will next go down the list of critical events that will precede and immediately follow ignition. He and Jack have practiced this most critical phase of the mission many times; nonetheless, Gene is making absolutely sure that they both remember exactly who is going to handle each of the tasks. The terms are defined below as the events occur.]
112:48:10 Schmitt: Roger. (Pause)
112:48:20 Fullerton: Challenger, we're going to leave Batt(ery) 3, Off...
112:48:22 Schmitt: (Garbled) Auto, Auto.
112:48:22 Fullerton: ...until after ignition. We'll call you.
[Batteries number 3 and 4 in the Descent Stage are hooked up in parallel and should be showing the same voltage. However, during battery warm-up in preparation for the descent, it was noticed that they had a voltage difference of about 0.5 volts. Although there are no other indications of a problem, Houston wants to take battery 3 off-line while they look at the performance of the electrical system. They will bring it back on-line at 112:55:13.]112:48:26 Schmitt: (To Fullerton) Roger. Yeah, I should have put that on like we talked about.
112:48:32 Cernan: (To Jack) Man, I'll tell you, we are getting close.
112:48:34 Schmitt: Looking out your window is really strange. (Laughing). From over here. (Long Pause)
RealAudio Clip by Roland Speth ( 8 min 03 sec )
MP3 Audio Clip ( 14 min 50 sec )
112:48:56 Cernan: One minute, Houston, and we're standing by. We're Go for PDI.
112:48:59 Fullerton: Roger. You're looking good here. (Long Pause)
112:49:19 Schmitt: Okay, approaching 30 seconds. Blank DSKY.
[Gene uses the Display and Keyboard Assembly (DSKY) to enter data and commands into the PGNS. It is located at his right hand, over the hatch. Jack uses the Data Entry and Display Assembly (DEDA) to monitor the AGS and, later in the descent, to enter trajectory corrections.]112:49:22 Cernan: DSKY blank. (Pause) Average G.
[Cernan - "When you go into something as dynamic as an engine burn, you get major fluctuations in the accelerometers and, to navigate effectively, you have to average the accelerations over a finite period of time."]112:49:30 Schmitt: Got two lights.
[In February 2009, Journal Contributor Paul Fjeld pointed out that Gene was mistaken about average g. See the discussion linked here.]
112:49:31 Cernan: Okay, Engine Arm is Descent. I think the tapemeter drove. I'm not sure. (Pause) Confirm the ullage.
[In other contexts, "ullage" is the empty portion of a cask. Here, the word is used to describe a 7.5 second firing of the Reaction Control System (RCS) in order to settle fuel in the tanks prior to ignition.]112:49:38 Schmitt: Standing by for ullage. (Pause) Ten seconds. (Pause) Fuel ullage. We've got ullage.
[Cernan - "At ignition, the tanks were about three quarters full of fuel and one quarter pressurized helium. The trouble was that, in zero gravity, you didn't know where the fuel was in the tank. Therefore, you had to apply a little acceleration and drive the heavy (that is, denser) fuel downward towards the outlet, towards the engine, so that, when you started the main engine you don't get a fistful of helium. Because we were flying with the landing gear and the main engine forward, to get proper ullage we had to fire the RCS jets briefly against that forward motion. We had the computer programmed to fire the thrusters for a few seconds prior to ignition; but, if Jack hadn't confirmed ullage, I would have used the handcontroller to give us manual ullage."]
112:49:51 Schmitt: Proceed on 99. It took. 2, 1, 0...
[Schmitt - "Having gotten ullage, we pushed the computer's Proceed button which told it to continue with engine ignition."]112:49:56 Schmitt: ...Ignition.
[Journal Contributor David Woods writes, "The software was written such that if the computer needed an input from the crew to allow it to proceed with its next function, it flashed a '99' in the display. The crew pressed the 'Proceed' button and the computer continued. This was usually used in the context of an engine ignition, as in 'Do you really want me to go ahead and light this thing?'."]
[Gene is prepared to do a manual backup of the engine ignition.]
112:49:57 Cernan: Ignition, Houston. Attitude looks good. Engine Override is On, Master Arm is Off. We got a Descent Quantity Light On at ignition, just prior to ignition.
[The Descent Quantity Light is an indication of an inadequate fuel supply. In this case, it is a false warning. Gene discusses his reaction to the warning at 113:11:55, after the landing.]112:50:04 Schmitt: DPC tank's good. RCS is good at 15 seconds.
112:50:10 Fullerton: Roger.
[We have been unable to translate "DPC" or find it in any list of Apollo acronyms. Undoubtedly, "DP" is "Descent Propulsion" and it is entirely possible that Jack got momentarily tongue-tied as he checked the propellant tanks and meant to say DPS for Descent Propulsion System.]112:50:11 Schmitt: RCS is golden. Should be stable throttle up. (Pause)
[Schmitt - "Probably, I was doing a quick check to make sure the tank pressures were okay. Evidently, the Quantity Light was giving a false warning."]
[For the first 26 seconds of the burn, the engine is fired at minimum thrust - about 10% of full thrust - so that the engine gimbal can be adjusted to put the thrust axis directly through the center of gravity. At throttle up, the engine is switched to full thrust, where it will remain until the last couple of minutes of the descent.]112:50:18 Schmitt: Stand by. There's...
112:50:20 Cernan: Throttle-up's on time, Houston.
112:50:20 Schmitt: ...throttle up.
112:50:21 Cernan: And the computer likes it.
112:50:23 Fullerton: Roger.
[Cernan - "Once you get into the computers, it's like riding a bicycle. Maybe you change to a different kind of bicycle, but it's still easy enough to learn. Long before we flew Apollo 17, I had gotten very comfortable with all of the computer systems. I had flown on Apollo 10 as Lunar Module Pilot and, on that mission, was responsible for a lot of things as far as computers were concerned, especially the AGS. Along with Tom Stafford, I also got to know the main computer to the point that I could sleep with it. After that flight I backed up Apollo 14. The morning of the Apollo 14 launch, I was ready to fly; and I knew those computers cold. And then came Apollo 17."]112:50:24 Cernan: (To Houston) Still got the Quantity Light on. (Pause) Okay, attitude looks good, Jack.
["The entry pad for the (PGNS) computer was between the two of us, by my right hand, just above the hatch. However, because of some experiences I had on Apollo 10 and so forth, I told Jack that, with very few exceptions, we weren't both going to be punching buttons on that main computer. On Apollo 10, Tom Stafford and I had had some trouble with the sort of situation where you think the computer's got one command and someone gives it another. Because of that, I told Jack that I was going to enter the commands and he was going to monitor me to make sure I did the right ones. He was going to run the AGS computer (with the DEDA, see below); but we weren't going to both be punching buttons."]
112:50:29 Schmitt: Okay. At 30 seconds (after ignition). Should have about 108 (degrees of pitch). (Pause)
[They are flying with their backs parallel to the lunar surface below them and their feet pointing in the direction of motion. Attitudes are being measured relative to the landing site. At the landing site, pitch is zero when the spacecraft is oriented vertically and would be 90 degrees if they were flying over the site parallel to the surface with their feet forward. At PDI, they are about 18 degrees east of the landing site and the local horizontal plane is tipped down 18 degrees to the east compared with the horizontal reference plane at the landing site. Consequently, the LM pitch measured in the landing site reference system is 108.]112:50:37 Cernan: (Marveling at the experience) Oh, boy!
112:50:39 Schmitt: AGS and PGNS are close.
[Schmitt - "The two, separate guidance systems had been initialized to the same data at some point prior to ignition. The AGS had some strapped-down gyros and wasn't as accurate as the PGNS; but, if the primary system failed, the AGS was certainly accurate enough to get us back to orbit. Here, I am checking to see that the two systems are in satisfactory agreement. Sometime prior to the mission I had worked out a way to update the AGS's knowledge of altitude by inputting a value from the radar data as soon as that became available. We'll see that later. LMPs were always trying to get the AGS to the point that, if you had to, you could land with it."]112:50:43 Cernan: Okay, coming up on 1 minute.
[Cernan - "We used to play around in the simulator to see if the AGS gave us enough information to land; and, quite honestly, if we were close I think we could have landed. There was a mission rule, as I remember, that we wouldn't land if we had a primary guidance failure. But one thing that people never paid much attention to is that, for most of the flight - and this is one very visible point - the ground has no control over what you're doing. They can send up information; but you're in command, you're flying the machine, and you're making the decisions. So who is to know what decision would have been made if you were down around three or four hundred feet or six hundred feet or a thousand feet and you had a question about your primary navigation system but your abort navigation system looked good. The AGS didn't have the landing radar tied into it, but it was giving you descent information and you could use those pieces separately. And who knows whether you would have landed or not. We didn't want to go that far and not land because of a computer problem."]
112:50:47 Schmitt: One minute. You ought to have 98 degrees of pitch. Okay, H-dot is high right now.
[H-dot is the descent rate, the time derivative of the altitude. They are descending faster than planned; hence, H-dot is high. The reason for this is that they are above the planned trajectory and the computer is bringing them down to it.]112:50:57 Cernan: Mark it, 1 minute.
112:50:58 Schmitt: Altitude's high.
112:50:59 Fullerton: Challenger, Houston. I have a 169...
112:51:02 Cernan: (Garbled under Fullerton) looks good, Houston.
112:51:03 Fullerton: ...plus 03400, plus 3400 feet. Over.
[Fullerton is giving them a target update. According to tracking data, the LM is headed for a point 3400 feet short of the planned landing site. Because this is a substantial error, Gene will enter a correction into the first register of Noun 69 ('169' in Apollo shorthand) in the computer so that it can modify the descent trajectory and put them on target. Jack will verify the entry.]112:51:11 Cernan: (To Fullerton) You're looking at it.
[Journal Contributor Paul Fjeld notes that the ability to update the LM targeting "was added on Apollo 12. DLAND - Noun 69 - was a dangerous vector! It was added to the Position of the landing site (RLS) every 2-second cycle, then zeroed. The crew had to verify that the three registers were all balls (all zero), then only put the Delta-Z value (downrange change in position) in R1, then only press enter when MCC looked at the DSKY downlist to verify that the number was good. Noun 69 was one of the easiest opportunities for the crew to kill themselves."]112:51:17 Schmitt: Okay; 3400. I confirm. (Pause) MP3 Audio Clip ( 13 min 13 sec )
[This clip was prepared by Colin Mackellar from recordings made at Honeysuckle Creek from Net 1 and provided by HSK Receiver Operator Alan Foster. The audio quaility is a bit better than the digitizations done from audio cassettes provided in 1989 by NASA Johnson.]112:51:23 Fullerton: Challenger, you're Go for Enter.
112:51:27 Cernan: Roger. Go for Enter.
[Cernan - "The ground couldn't fly the spacecraft or do anything with it, but they could read a lot of the data out. While I keyed the new data into the computer and Jack verified it on-board, they could also read it and verify it on the ground. Normally, they'd look at it and verify it before we'd go ahead and actually execute whatever command or (enter) whatever data they'd given us."]112:51:29 Cernan: 1:30. We're Go coming through 57K.
[They are one minute and thirty seconds into the burn and are at an altitude of 57 thousand feet, or about 17 kilometers, above the lunar surface.]112:51:31 Schmitt: Okay, the altitude's high and the H-dot is high. At least...That's right. (Pause) Okay, at one...(Correcting himself) At 2 minutes, you ought to have 89 on the ball.
[Cernan - "We had an inertial attitude gyro, like in an airplane, which we called the "eight ball" or simply the "ball". It was essentially fixed in space and we would rotate the spacecraft around it. With the LM sitting on the lunar surface, the ball would have shown a pitch of zero degrees; and, while we were in the initial descent and lying on our backs with our feet forward, looking up at the sky and slowing down, it would show about 90 degrees or maybe even 108, depending on the trajectory. As we drifted in, we slowly pitched upright until, at 60 or 70 degrees pitch and 7000 feet altitude, we'd go through the big pitchover."]112:51:43 Schmitt: We're still 30 feet per second high in H-dot. But we're about 8000 feet high...
112:51:48 Fullerton: Challenger, Houston,...
112:51:49 Schmitt: ...(make that) 7000 (in altitude).
112:51:51 Fullerton: ...we'd like you to cycle the PQGS switch Off and then back On.
[PQGS is the Propellant Quantity Gauging System. Cycling the switch will let them see if the quantity warning light is real.]112:51:52 Cernan: Okay, Houston. Coming up on 2 minutes. (Pause as he listens to Fullerton) Okay. It (meaning the switch)'s Off. And it's back On. Quantity Light is out.
112:52:06 Fullerton: Roger. That should be good now.
112:52:09 Cernan: And, Houston, we...(Hearing Fullerton) Okay. We have Engine Thrust and Commanded Thrust, full-scale high.
112:52:18 Fullerton: Roger.
112:52:19 Schmitt: Man, that looks good.
112:52:20 Cernan: Okay, babe, let's check them at 02:30.
112:52:22 Schmitt: RCS looks good.
112:52:27 Cernan: 02:30, I'm about 89 degrees...
112:52:28 Schmitt: Cabin looks great...
112:52:30 Cernan: ...coming through 51.5 thousand feet.
112:52:31 Schmitt: 89 is great. 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. And we're north; (AGS) has us north of track.
[That is, the AGS is showing them north of the planned ground track. Jack will ask the question again in about 2 minutes.]112:52:52 Fullerton: Challenger, Houston...
112:52:53 Cernan: Okay, Gordo; coming up on 3 minutes, we're Go and...
112:52:54 Fullerton: ...you're Go at 3.
112:52:55 Cernan: ...we're out of 49K. (Hearing Fullerton) Roger. Understand we're Go.
112:53:03 Schmitt: Okay. At 3 minutes. 82's your ball number. We're still looking for (that is, coming down to) the right altitude. So H-dot is high.
112:53:13 Cernan: Okay. (Pause) The day of reckoning comes at 4 minutes, Jack. (Pause) Got the weight building up, looking good. Attitudes are good.
112:53:30 Schmitt: Okay, at 03:30, you ought to have 79...
112:53:33 Cernan: Okay, it's right on.
112:53:35 Schmitt: We're still a little high, about 2500 feet (high). H-dot is still high. (Long Pause)
[In the last two minutes, the altitude error has decreased from 7000 feet to 2500 feet and has closed, therefore, at a rate of 40 feet per second. At PDI, they were about 30 degrees of longitude east of what would have been the closest approach to the surface (perilune) of their pre-PDI orbit. Being east of the perilune, they were already descending toward the surface at a rate of about 67 fps - a rate which would have slowed in the absence of the burn - and they had planned to maintain that rate of 67 fps for the first seven minutes of the burn. Having started out above the planned trajectory, their total rate of descent has been a bit above 100 fps.]112:53:50 Cernan: Okay. The tapemeter moves in spurts and jerks, both on altitude and altitude rate (in response to the first radar returns from the surface).
112:53:56 Schmitt: Yeah.
[Schmitt - "There was a tapemeter display for showing the radar data - altitude and altitude rate (H-dot) - when that became available. Physically, it was a pair of tapes with numbers on them which moved up and down behind a needle."]112:53:58 Fullerton: Challenger, Houston. You're Go at 4 minutes.
[Cernan - "We had so many rate needles that it's a little hard to remember; but we could change them to show a lot of things like altitude and altitude rates. I think we could change this particular tapemeter (which was next to the "8-ball" attitude indicator on Gene's side of the spacecraft) showed either the radar data or the computer's best guess about the altitude and altitude rate."]
112:53:59 Schmitt: ED Batts are 37.2 (volts).
[These are batteries that supply electricity to the explosive devices which would separate the Ascent Stage from the Descent Stage in the event of an aborted landing attempt using the ascent stage to return to orbit. Jack will check the batteries periodically.]112:54:02 Fullerton: Roger. ED Batts.
112:54:04 Schmitt: ED Batts are 3...(Listening) Okay.
112:54:07 Cernan: Okay, Gordo, yaw's coming at 340.
112:54:11 Fullerton: Roger.
[See Gene's comment at 112:56:33. This yaw maneuver - a rotation around the thrust axis - is designed to put the landing radar in optimum position. Prior to ignition, they had the spacecraft yawed left by 70 degrees for optimum communications with Earth and are now reducing that to 20 degrees left. Once they get down to an altitude of 30,000 feet, they will go to a zero-yaw, windows-up attitude for the landing.]112:54:15 Cernan: And the radar lights are out! Beautiful.
[The radar has acquired the lunar surface.]112:54:19 Fullerton: Okay, sounds great. Both Nav systems are Go...
112:54:21 Cernan: You're looking at Delta-H.
112:54:22 Fullerton: ...right on the line.
112:54:26 Cernan: Okay. You're looking at Delta-H.
[Schmitt - "This was the difference between the radar altitude and the PGNS calculated altitude"]112:54:28 Fullerton: And you're Go for a Verb 57.
112:54:34 Cernan: Okay, Verb 57 is in.
[Schmitt - "Verb 57 allowed the radar data to be incorporated into the computer."]112:54:38 Schmitt: Hey, Houston, is the AGS (indication that they are) out-of-plane correct?
112:54:42 Fullerton: Stand by. (Pause)
[Cernan - "We had gone into lunar orbit in the CSM on a path that went from northeast to southwest across the front face of the Moon. That track took the Command Module over the landing site but wasn't exactly the right path for the final approach. So we flew the LM a little south out of the CSM orbital plane so that we could line up with our runway, so to speak, down the axis of the valley."]112:54:47 Cernan: Okay, coming up on 5 minutes, Jack. Let's take a check at it. About 74 degrees (of pitch).
112:54:51 Schmitt: That's good. 70 feet per second (descent rate); we're coming down. 36...You're still (garbled, either "two" or "three") thousand feet high;
112:54:56 Fullerton: Challenger, you're Go at 5 minutes...
112:54:57 Cernan: Okay, Houston; we're now out of thirty...(Stops to listen)
112:54:58 Fullerton: ...the AGS out-of-plane looks okay to us. (Pause)
[Fullerton will give them a fuller explanation of the out-of-plane indication at 187:40:10, just prior to launch.]112:55:04 Cernan: Okay. Go at 5. We're out of 36.5 (thousand feet) now. We've got the Earth right out the front window. (Pause)
[Cernan - "We landed so far east and north that the Earth was in the southwestern sky above the mountains. Every other flight landed where the Earth was essentially overhead; so ours was unique in that, during our descent, we were looking right at the Earth as we were coming down in the valley. As those mountains rose above us, we were looking at the Earth - I mean - right smack in front of us! We didn't have to look up at it; it was right there. Can you imagine coming down, thirty-six thousand feet above the lunar surface and all of a sudden, almost nonchalantly, saying that you've got the Earth right out the front window? And all the other things going on at the same time?"]112:55:13 Fullerton: Challenger, Houston. Battery 3, On, at your convenience.
112:55:22 Schmitt: Battery 3 is On.
[They are about fifty miles from the landing site.]112:55:25 Cernan: 05:30, Gordo. We're Go. We're out of 34K.
112:55:28 Schmitt: 73 (degrees), 34 (thousand feet). We're right on altitude. The H-dot ought to start dropping off. Except that we want to keep it high.
[Their average descent rate during these 5.5 minutes has been 100 fps, with about 30 fps of the total due to the descent to the planned trajectory. Now, they are on the nominal flight path and Jack's "we want to keep it high" may be a reference either to the fact that the rate will start to increase again once they get down to about 32,000 feet or to the altitude/altitude rate chart he has been consulting. If this is a reference to the chart, he may be saying that they want to stay in the constant rate portion of the graph for a while longer.]112:55:38 Cernan: (With a slight tone of authority, to Jack) You're allowed two quick looks out the window, one now and one when we pitchover.
112:55:41 Schmitt: I can't see a thing except the Earth.
112:55:43 Cernan: That's what I'm telling you to look at.
112:55:45 Schmitt: (Laughs) Oh! There's the old Earth!
[Cernan - "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 gauges, looking at battery currents, updating the AGS computer, 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. Actually, I had to look both places - inside and outside - but my primary focus was out the window and on all of the attitude and rate indicators that surrounded the window. My peripheral scan was forward, out the window, and to the instruments that surrounded it, and occasionally down to the computer when I had to execute a command with it. But poor Jack had to keep his head buried in the cockpit."]112:55:48 Cernan: Okay, Houston, coming up on 6 minutes.
112:55:51 Schmitt: (At) six minutes, you ought to have 72 on your ball.
112:55:56 Fullerton: Challenger, you're Go at 6 (minutes).
112:55:57 Cernan: 72 is Go.
[They are 40 miles east of the landing site.]112:55:59 Schmitt: 31 (thousand feet). Altitude's great. H-dot's great. AGS and PGNS are very close, couple feet per second (descent rate) difference.
112:56:07 Cernan: Okay. (Pause) Okay, Houston. As we went over the hump, Delta-H just jumped.
112:56:16 Fullerton: Roger.
[Cernan - "The PGNS was keeping track of our altitude relative to the landing site while the radar, of course, was getting raw data from the terrain below us. Knowing ahead of time that we were going to cross the mountains east of the landing site, we were looking for the altitude difference to change, and it was a comfortable feeling to see it happen."]112:56:18 Cernan: And looks like it's back down.
112:56:21 Fullerton: Roger. Sounds good.
112:56:25 Schmitt: 6:30, Geno.
112:56:26 Cernan: It looks good, babe.
112:56:29 Schmitt: 72 (degrees). Altitude is right on. H-dot is very close.
[Jack is consulting a graph of the expect altitude, descent rate, etc versus time during the burn. The graph is mounted on the yellow AOT guard in training photo KSC-72PC-539.]112:56:33 Cernan: Okay, 30K, Yaw to zero (that is, "windows-up" for the landing).
[Cernan - "The pitch, roll, and yaw axes were different on the LM than they were on the Command Module; and we had re-defined them for pilot convenience. Pitch was rotation around the left/right axis; roll was rotation around the axis out the front window or the front hatch; and yaw was rotation around the thrust axis. When you were coming down in the final approach and were pitched straight up, if you looked out the window at a particular point and yawed left, that point would move right in your window."]112:56:36 Fullerton: Throttle down time (will be) 7 plus 26.
112:56:43 Schmitt: 7 plus 26.
[They have killed all but 1000 fps of their initial 5500 fps orbital velocity and will now descend at reduced thrust, initially 57 percent of full thrust.]112:56:46 Cernan: Okay, we got everything? We're Yaw at zero. (Pause)
RealAudio Clip (6 min 50 sec)
112:56:59 Schmitt: Okay. At 7 minutes, 67's your angle. 26...(Correcting himself) 27; that's great (garbled)...
112:56:59 Fullerton: Challenger, you're Go at 7.
112:57:00 Schmitt: ...H-dot's slightly high, but okay.
112:57:03 Cernan: Okay, Gordo. We're Go at 7, we're now out of 25,000 feet.
112:57:08 Schmitt: We're quite a bit out of the Command Module plane, but I guess we're on target.
112:57:14 Cernan: Okay, watch the throttle, now. Here it comes. (Pause)
112:57:21 LM Crew: Throttle down
112:57:22 Cernan: (It came at) at (7:)27; computer likes it.
112:57:25 Schmitt: Beautiful.
112:57:26 Fullerton: Roger.
112:57:29 Schmitt: Okay, 07:30, 63 (degrees).
112:57:31 Cernan: Okay, 1:45 to pitchover, Jack.
[That is, one minute forty-five seconds.]112:57:33 Schmitt: Okay, 63's your angle
112:57:35 Cernan: About 56 now.
112:57:40 Schmitt: Okay, that's getting closer. (Pause)
112:57:42 Schmitt: H-dot and H agree. Standing by for the camera.
[Jack has been comparing computer readouts for H and H-dot with expected values shown on a chart. Both quanities now agree with the expected values. The raw transcript prepared at the time of the mission for the press has the first part of Jack's transmission as "H-dot and H are great". In December 2011, Colin Mackellar noted - and I concur - that, in recordings made at Honeysuckle Creek, Jack seems to be saying "H-dot and H agree". ]112:57:50 Cernan: 19K, Houston. We're Go coming up on 8 (minutes).
[Shortly, Jack will start the sequence camera, a sixteen-millimeter movie camera mounted in Jack's window as shown in training photo KSC-72PC-539. As of mid-1993, the film from this final descent was being shown over and over again as part of a LM cabin display at the National Air and Space Museum in Washington, D.C.]
[Ten miles out.]112:57:55 Schmitt: Okay. The old camera's on, Gordy. Believe it or not.
112:57:58 Fullerton: How about that. You're Go at 8. Monitor fuel, 2.
[Schmitt - "There were at least two fuel gauges and, after watching their telemetry, the ground recommended which one we should use as a better indicator of fuel quantity."]112:58:03 Schmitt: Fuel 2: (is reading) 27. That's good.
[Cernan - "We used a lot of numbers and commands that didn't mean anything to most people. But, when you'd done the training and were using the numbers in context, you didn't need to put dimensions with them. All you said was 'Hey; Fuel 2, 27.' And, at the time, that meant something to us. You knew the systems and you knew what that 27 was supposed to mean and that it wasn't supposed to be 92 or 22. And you knew whether it was supposed to be gallons or pounds or whatever. You just talked in an abbreviated language because you were almost in a world of your own during that time, talking to each other with things happening in rapid sequence. Not a lot of people knew what you were talking about, except for the two of you and the people on the ground."]112:58:09 Cernan: Come on, baby.
112:58:13 Schmitt: Okay, at 08:30, Geno.
112:58:17 Cernan: Okay, I got the South Massif.
[Gene's altitude is about 16,000 feet and the pitch angle is about 60 degrees. He is seeing the summit of the South Massif out the bottom of his window.]112:58:19 Schmitt: Okay, update the AGS, Houston? Yes.
112:58:26 Fullerton: That's affirmative; update the AGS. (Pause)
112:58:35 Cernan: Okay, Gordo, I've got Nansen; I've got Lara; and I've got the Scarp. (Five miles out.) Oh, man, we're level with the top of the Massifs, now.
Apollo 17 Landing Movie by Gary Neff (3 minutes 32 seconds); (4.8 MB)
112:58:45 Fullerton: Roger.
[They are five miles east of the landing site. Nansen is a large depression at the foot of the South Massif; the Scarp is a fault scarp that runs from Nansen northward across the entrance of the valley and up on to the North Massif; and Lara is a crater at the base of the Scarp about midway between the North and South Massifs. At this point, they are at about 12,500 feet altitude, about 5000 feet above the summit of the South Massif.]112:58:47 Schmitt: Okay; (possibly reading the DSKY) 151, (possibly putting the numbers into the DEDA) 1510 entered.
[Cernan - "We landed in a valley that had mountains higher than the Grand Canyon is deep. Prior to pitching over, down in the bottom of the windows, the first thing I could pick out was the top of the mountains. And as we pitched up some more, I could begin to identify things in our valley. I had to lean as far forward as I could to look up over the top (of the window sill), but I could see them. And it seemed like we were down below the tops of those mountains, down into the valley. It really did. Maybe we were still above the tops; but, as far as I was concerned, we were in that valley."]
[Schmitt - "This was a number going into the AGS to give it a new altitude reference; and it was taken off the computer which now had the radar update. When the ground agreed that the data was good, then I put it into the AGS for abort purposes. This was something I worked out with the AGS people; I was always trying to find a way to make the AGS better, and this was one of the things."]112:58:52 Cernan: Okay, Jack...
112:58:53 Fullerton: Challenger. You're Go at 9 (minutes).
112:58:55 Cernan: ...pitchover is at (nine minutes and) 24 (seconds into the burn); 24 on pitchover. Okay, Gordo, we're out of 11,000 at 9.
112:59:01 Schmitt: Okay, stand by for pitchover.
112:59:04 Cernan: Oh, are we coming in. Oh, baby.
112:59:11 Schmitt: Okay; through 9000.
112:59:12 Cernan: Stand by for pitchover, Jack.
112:59:14 Schmitt: 8000.
112:59:15 Cernan: I'll need the Pro(ceed).
112:59:16 Schmitt: I'll give it to you.
[Schmitt - "By hitting the Proceed button, the computer would start the next program in its repertoire. There was a whole series of programs called P64 and the like, this one being the program for events after pitchover."]112:59:18 Cernan: Pitchover.
[Cernan - "Pitchover was very critical. I needed to look out the window to make sure the LM didn't pitch over too far; so this was one of the few instances in which we had planned for Jack to enter a command into the computer so that I didn't have to look down. Learning how to work together during the landing sequence was a critical part of our training. You get procedures, you get checklists, but two guys still have to learn how to work together and coordinate their resources effectively. This is a good example of that, and one that was much more critical than the lunar surface work."]
112:59:19 Schmitt: There it is! Proceeded.
[Cernan - "We still wanted to slow ourselves down by firing forward but now we also had to keep ourselves from falling in too fast toward the surface. I don't know how much we pitched over, maybe from about sixty degrees to about twenty or thirty degrees (actually from 60 degrees to 20); but, when we did, all of a sudden, bam, the lunar surface filled up almost the entire window."]112:59:21 Cernan: And there it is, Houston. There's Camelot (Crater)! Wow! Right on target.
112:59:24 Schmitt: Wow! I see it.
112:59:25 Cernan: We got them all.
[Cernan - "Although there is nothing quite like the real thing, flying the Lunar Landing Training Vehicle (LLTV) had been a step toward realism from "flying" the stationary simulators. In the LLTV you had your butt strapped to a machine that you had to land safely or you didn't make it. It still wasn't landing on the lunar surface, but it gave you a feel for what the actual landing would be like. Similarly, in simulator training we'd had a TV picture of a (large) model of the landing site that was good enough that, when we pitched over during the actual landing, I felt like I'd seen the landing site before. I won't say that I totally felt like I'd been there before, but I felt like I'd seen that valley before, three dimensionally. So it was a very comfortable feeling to know we were right where we expected to be."]112:59:26 Schmitt: 42 degrees, 37 degrees through 5500. 38 degrees...
[Camelot Crater has a diameter of about 600 meters and the planned landing point is about 600 meters east of its eastern rim. Camelot is also the westernmost of a group of large craters that are scattered around the center of the valley and is a very easily recognized landmark.]
[Cernan - "In addition to all the fancy gear, all the rate needles and everything, when it came right down to landing, we had etchings on the window in both pitch and yaw (part of the Landing Point Designator or LPD). And here, after pitchover, Jack is telling me where on the window the computer thinks we're going to land. The digital autopilot and the computer programs were designed to accept attitude impulses with my handcontroller. I could go "blip" once and that would tell the computer that I wanted to change the target maybe a half degree or a degree in pitch. In effect, I was saying, 'Computer, I am now smarter than you. You think you know where the target is, but I'm looking at it out the window. I know where it is, and I'm going to tell you.' It was the same sort of thing in yaw, but you have to remember that yaw didn't directly change the flight direction because yaw is a rotation around the thrust axis. If I rolled to the left, I was going to put the engine to the right and drive myself to the left. If I pitch up, I'm going to put the engine more forward and I'm going to slow myself down and start to come down faster. But I could have yawed through 360 degrees and never effected my trajectory. So if I blipped the handcontroller in yaw, what it really said to the computer was that I wanted to land a little left and that it had to do a little roll to get over there."] [Randy Attwood has provide a photo of the LPD scale in LM-9, the H-mission-capable vehicle scheduled for Apollo 15 before that flight became a J-mission.]112:59:32 Fullerton: Challenger, you're Go for landing.
112:59:34 Schmitt: ...5000 feet; 42 degrees (LPD angle) through 4000; 47 now; 47 degrees through 3500; 49 degrees. (Pause) 3000 feet; 53 degrees.
[Cernan - "The fact that the target numbers are increasing doesn't necessarily mean that we were pitching up very much, only that we were getting closer to the target and, therefore, that it was getting higher in the window. I didn't respond to these because I was looking out the window and, if I needed to move, I just moved the handcontroller."]112:59:54 Cernan: Okay, I've got Barjea; I've got Poppie; I've got the Triangle.
[The Triangle is trio of small, well-separated craters - Frosty, Rudolph, and Punk - west and north of the landing site. The Triangle is distinct from a merged-crater triad called Trident, south of the target point.]112:59:59 Schmitt: At 2500 feet, 52 degrees. H-dot 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 and PGNS altitudes agree. You're through 800 feet. H-dot's a little high.
[Cernan - "Poppie was my daughter Tracy's name for my father (Andrew 'Andy' Cernan). He never lived to see me land on the Moon and I named the crater for him. And Punk is what I used to call Tracy. I still do, even though she's twenty-six years old (January 1990)."]
[Readers will note that "Poppie" is mis-spelled as "Poppy" throughout the Apollo literature, including the maps that are reproduced in this Journal.]
[In 1997, Journal Contributor Brian Lawrence suggested that Barjea was named for Gene's wife, Barbara Jean, with the name disguised both by spelling and by Gene's Spanish-like pronounciation, 'Bar-HEE-a'. In a brief correspondence, Gene confirmed Brian's suspicion.]
113:00:28 Cernan: Okay; I don't need the (LPD angle) numbers any more.
[Cernan - "The angles were useful from pitchover until we got down to a thousand or two thousand feet, and then you were flying by the seat of your pants to some degree. Besides, now I was looking at where we wanted to land, and was just putting it there. So I didn't need the degree numbers, just the altitude and descent rate."]113:00:32 Schmitt: Okay, you're 31 feet per second, going down through 500. 25 feet per second through 400. That's a little high, Geno.
[Schmitt - "A lot high!"]113:00:40 Cernan: Okay.
[The nominal descent rate at 500 feet is 17 fps.]
[Cernan - "I had it under control; I knew what the response was and how quickly we could slow down. It was comfortable and it saved fuel. In the Navy, we land aboard carriers at 15 feet per second and I knew what that was; and I'd flown the LM Simulator so many times that I knew what 15 feet per second at 100 feet was like and knew that I could slow it down to 5 feet per second awfully quickly."]
113:00:42 Schmitt: 300 feet, 15 feet per second. A little high. H-dot's a little high.
[The nominal descent rate at 300 feet is 9 fps.]113:00:51 Cernan: Okay. I've got P66.
[Up to this point, Gene has been using the handcontroller to tell the computer to move the designated landing point forward or back, left or right. In P66 he takes manual control of the spacecraft and uses the handcontroller to change its attitude in pitch and roll. In short, he is now flying the LM with virtually no assistance from the computer.]113:00:55 Schmitt: Okay; 9 feet per second down at 200. Going down at 5. Going down at 5. Going down at 10 (fps); cut the H-dot. The fuel's good. 110 feet. Stand by for some dust. Little forward, Gene.
[Here, Jack is confirming that Gene has a little forward velocity so that he'll land on ground he's just seen.]113:01:14 Cernan: (Garbled under Jack)
[Cernan - "The tendency for most people flying the LM was to get a false impression of thinking that you were coming down straight. But, because of where the window was located, you would actually be drifting backwards. So I forced myself to land with about a foot or a foot-and-a-half forward velocity. And then, if I fell into the trap of feeling that I was going forward when I was really going vertical, it would be okay."]
113:01:15 Schmitt: Moving forward a little. 90 feet. Little forward velocity. 80 feet; going down at 3. Getting a little dust. We're at 60 feet; going down about 2. Very little dust. Very little dust, 40 feet, going down at 3.
[Gene wants about 5 feet per second down for the final phase; 2 feet per second would burn too much fuel and oxidizer. They will land with about 1225 pounds of fuel remaining, enough for about 117 seconds of hovering. For comparison, Neil Armstrong landed with only 50 seconds of fuel/oxidizer remaining, primarily because at pitchover he discovered he was coming down into West Crater and had to take over manual control quite early and fly beyond to a good landing spot. Apollo 11 was the only flight on which less than 100 seconds of fuel/oxidizer remained at touchdown.]113:01:42 Cernan: Stand by for touchdown.
[In the landing film, dust becomes easily visible at about 113:01:38; but, by this time, Gene knows exactly where he is going to land. Even in the film, rocks and small craters are visible until the last few seconds. The 16-mm camera is mounted in Jack's window.]
113:01:43 Schmitt: Stand by. 25 feet, down at 2. Fuel's good. 20 feet. Going down at 2. 10 feet. 10 feet.
113:01:58 Schmitt: Contact. (Pause)
[The Apollo 17 Mission Report indicates that Contact occurred at 19:54:58 UTC 11 December 1972. Note that, because of the 2 hour 40 minute launch delay, NASA altered the spacecraft trajectory so that the crew would enter lunar orbit and make the landing at the planned times. During the trip out to the Moon, Houston put the mission clocks forward by that amount so that the clocks would agree with times shown in the checklists, which are relative to the planned time of launch.]113:02:03 Schmitt: (Reading a checklist) Stop, push. Engine stop; Engine Arm; Proceed; Command Override, Off; Mode Control, Att(itude) Hold; PGNS, Auto.
[Journal Contributor Jim Scotti writes, "I once asked Gene Cernan what sort of sounds he had heard as he landed on the Moon, hoping to get answers to these kinds of questions - how loud the thrusters were, could he hear the descent engine, what about pumps and switches and anything else. What he said was rather different than what I was expecting. He said that what he heard in the moments after landing was... silence! You see, before landing, he was so engrossed in the activity that he heard Jack calling out numbers and the occasional call from Houston and everything else blended into the background because he was so focused on the task of landing. At touchdown, however, the spacecraft fell silent and mission control was staying quiet to try not to interfere with what they expected was the final moments of touchdown. And Gene added: 'And the guy standing next to me was struck silent staring out the window looking at the surface and he sure wasn't saying anything!' So Gene noticed the silence. Cool perspective! It fit exactly the kind of answer that I would have hoped for, even though it wasn't the kind of details I had hoped for, but it did a really great job of putting me in his boots at the CDR station in the LM just after landing at Taurus-Littrow."]
113:02:11 Cernan: Okay, Houston. The Challenger has landed!
113:02:15 Fullerton: Roger, Challenger. That's super.
113:02:17 Schmitt: Okay, Parker valves...
[Schmitt - "Parker valves (also known as the isolation valves or shut-off valves) controlled the RCS thrusters - the fuel and oxidizer - and there was always some concern that they might close at landing, just because of the little bit of shock. So the procedure was to go through and cycle (close and open) every one of them. There were, I don't know, sixteen of them on the wall in front of me and, while Gene was getting all excited, I was cycling switches."]113:02:23 Cernan: (Responding to Fullerton) Boy, you bet it is, Gordo. (To Jack) Boy, when you said shut down, I shut down and we dropped, didn't we?
113:02:28 Schmitt: Yes, sir! But we is here.
113:02:30 Cernan: Man, is we here.
[Cernan - "In thinking about why we worked so well together, the most important point was that we had confidence in each other. Jack is a very astute and dedicated individual, very talented, and I felt very comfortable with him. He was not an aviator and he'll be the first to tell you that. But he took his responsibilities very seriously, learned quickly, and, in terms of technical understanding, was as good as anybody. He wasn't a passenger; he had learned how to be a good co-pilot. In much the same way, I wasn't a geologist, I wasn't a scientist; but I had learned to be a good observer. As soon as we hit the lunar surface, although I was still commander of the crew, Jack was the expert and I was his assistant. We had very different backgrounds. I was the professional aviator and Jack was the scientist; but we both knew enough about all aspects of the missions that we could be confident about working together."]113:02:31 Cernan: How does that look? That looks good.
[In the next paragraph, the terms 'left seat' and 'right seat' are carryovers from aircraft useage where the commander sat on the left and the co-pilot on the right. Although the LM has no seats, Gene is referring to the Commander as the 'guy in the left seat' and the LMP as 'the guy in the right seat'.]
[Cernan - "For the landing and lift-off phases, we were both dedicated to knowing all the intricacies of the spacecraft, all the details of the hardware and the software. Our responsibilities were different; but the fact that I knew all the systems on his side and he knew all the systems on my side was important. I'm the kind of guy who, although I knew I could depend on Jack, wanted to understand everything about the spacecraft. I was fortunate because I'd sat in the right (LMP) seat on Apollo 10, so I knew the AGS (Abort Guidance System). I knew what it could do and, when Jack would talk to me about the AGS or how we were going to use it, I understood because I had been there. And Jack took it upon himself to be very familiar with the operation of the primary guidance computer (PGNS) and the other systems on my side of the spacecraft. But I know there were crews - and I won't name them - where one or the other of the guys was extremely weak in one or more of the systems. Crews where, if the guy in the right seat told the guy in the left seat something was right or wrong, the guy in the left seat just accepted it because he didn't know any different. And he didn't know enough to ask any questions. If the guy in the left seat is just going to depend on someone to throw him a number and not know what the number means or where it came from, and can't challenge it, can't know whether it's right or wrong, then he's not doing his job. With me, if it was ten degrees off, I would know it. And I'd say 'Jack, check your AGS; that's not right.' But if the guy in the left seat had no idea what the AGS was supposed to do, he might just blankly accept that number and go about his business and might or might not get in trouble as a result of it. Even a computer isn't right all the time, and certainly people are prone to mistakes; but if two guys both know a system you're least likely to make a mistake. Mutual respect and teamwork evolves from that."]
["Landing on the Moon was a unique opportunity for us both; we didn't want to let it slip through our hands. We spent the time that it took: not just a few extra hours in the simulator, but all the time it took to really understand our spacecraft. Jack spent a lot of time with the people on the ground - more than I did. He got to know them and understand them. He'd go to them with questions like, 'How can you guys help me get my AGS smarter than it normally would be.' And, because he'd spent time working with them, they said 'Hey, we can work something. We'll put it into the checklist that we'll send you an update here and you do that there.' And those kind of things paid off in the form of a level of coordination and teamwork between us and the people on the ground that was as good as on any mission."]
["By the same token, I had a lot of personal pride that, if we had lost three quarters of our automatic systems, I still could have landed the vehicle safely. Same thing for leaving the lunar surface. True, you have to believe that you can do it; you would have no other choice. But I knew that if we lost all of our guidance computers, I could have flown that LM into lunar orbit for a rendezvous with Ron Evans. Manually. And by 'manually', I mean (visually guiding) with the stars (and) with the horizon of the Moon. I'd done it enough in the simulators that I knew what my remaining systems were going to tell me; and I had confidence that Jack was going to give me whatever information I need from him. You never know (if you're right about something like that), but I'm confident that we could have done it. And I felt the same way about the Saturn V launch from Earth. Ours was the first nighttime launch, and there were a lot of things we had to consider in terms of guidance control failures. The launches - both from the Earth and from the Moon - were the only truly automatic phases of the mission, but we could take over and fly it manually to orbit. Aborting during Earth launch was the last thing I wanted to do, so I trained and planned. It was a lot more difficult at night than in the daytime because you didn't have horizons and things to look at; you had to look at the stars. We had several modes of failure that could have degraded systems. The worst would have been for all the guidance to fail so that you literally had to fly it by the stars. Now, I can never prove that I could have done it. But I did it a lot of times in simulators and really did - and still do - believe that I could have flown that Saturn V to orbit. It's one of those things where you say 'I hope it never happens; but I dare you. I'll show you. If you do fail, you just watch.' You had to have that attitude; and I think that attitude is reflected across the cockpit. You develop confidence in each other, and, from that, the teamwork evolves."]
[For the next several minutes, Gene and Jack will monitor the health of their spacecraft and prepare it for an immediate launch, should one prove necessary.]
113:02:35 Schmitt: Pressures look great. Tank 2 is down just a little from before.
113:02:39 Cernan: Okay, Engine Override is Off (garbled)...
113:02:40 Schmitt: Manifold (pressure) is great. Manifold is right on. Go to Jets.
113:02:44 Cernan: Okay. I am Jets.
113:02:46 Schmitt: Okay. That side's complete.
[They have probably completed one side of a cue card.]113:02:48 Cernan: Houston, you can tell America (that is, Ron Evans) that Challenger is at Taurus-Littrow.
113:02:53 Fullerton: We'll do it.
113:02:56 Evans: Hey, Challenger; this is America. I heard you all the way down. That's great! Beautiful.
113:03:00 Cernan: (To Evans) Ron, I had the meatball all the way.
113:03:02 Evans: Beautiful!
[Cernan - "When you land on a carrier, you've got a mirror and you've got an orange light that reflects in the mirror. On the carrier you've got a row of green lights that also reflect in that mirror and if the meatball - the orange light - is below the green lights, then you are low, below the glide slope; and if the meatball's above the green lights, you are high. So what you do is fly your carrier approach so that the meatball is right in line with the green lights. So I was telling Ron that I had it 'locked' all the way in."]113:03:02 Cernan: Jack, are we going to have some nice boulders in this area.
113:03:08 Schmitt: Okay. The old (16-mm sequence) camera's off.
113:03:10 Cernan: Okay.
113:03:13 Schmitt: Landing Radar (circuit) breaker, Open. Checking the water (tank). And, Gordy, ascent tank 1...We started out a little low (but) it's still...same place. That's water.
113:03:27 Fullerton: Roger, Jack
113:03:28 Schmitt: Batteries look good. (Pause) (Very excited) Oh, man!! Look at that rock out there! (Pause)
[Jack is probably looking at a 3-meter-high basalt boulder about 200 meters west of the spacecraft. It is now known as Geophone Rock and is just to the left of the LM shadow.]113:03:40 Cernan: Absolutely incredible. Absolutely incredible.
113:03:45 Schmitt: I think I can see the rim of Camelot.
113:03:47 Fullerton: Roger.
113:03:48 Cernan: Epic moment of my life.
[During the descent, Gene's heart rate reached a peak of 97 beats per minute. The details are shown in the upper portion of Figure 11-1 in the Apollo 17 Mission Report. For comparison, Neil Armstrong's peak rate was 150 - due mostly to the stress of having to avoid West Crater - while the rates for the other three Commanders for whom we have data were 110 for Alan Shepard (Apollo 14), 105 for John Young (Apollo 16), and 97 for Dave Scott (Apollo 15).]
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