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Landing at Descartes

Corrected Transcript and Commentary Copyright © 1996 by Eric M. Jones.
All rights reserved.
Scan credits in the Image Library.
Video credits in the Video Library.
Except where noted, audio clips by Roland Speth.
Last revised 18 December 2011.

[At 74 hours 28 minutes 28 seconds in the mission of Apollo 16, the crew fired the Command and Service Module (CSM)'s Service Propulsion System (SPS) engine to put themselves into a 170 by 58 nautical mile elliptical orbit around the Moon. The low point of this orbit was over the Lunar Farside at the point at which they had entered lunar orbit; the high point was roughly over the Descartes landing site. Four hours later, after completing two orbits of the Moon, the crew fired the SPS engine for a second time to put themselves in a new orbit, one with a high point of 58 miles and low point of just 11 miles. In this "Descent Orbit", the high point was over the lunar Farside, still roughly at the point at which the crew had first entered lunar orbit, and the low point was east of the landing site. From this low point on a later orbit, the LM crew would begin their descent to the lunar surface. Note that the low-point of the Descent Orbit had been planned as 8 miles, but the difference between 8 and 11 was not deemed significant enough to warrant an additional SPS burn.]

[After an eight hour rest period, the crew awakened at about 91 hours 30 minutes and, at about 93 hours, Commander John Young and Lunar Module Pilot Charlie Duke entered the Lunar Module Orion to begin their power-up and checkout procedures. It was at this point that the first of three notable hardware problems were discovered. The first two were LM problems that were resolved with relative ease. The third was a far more serious CSM problem that ultimately resulted in a three-orbit delay of the landing.]

[Duke - "Before PDI (Powered Descent Initiation), I remember two major problems. As we started powering up the LM, our high-gain antenna didn't work in one of the axes - I believe it was yaw. And we never could shake it loose."]

[Because the spacecraft attitude relative to Earth changed constantly as the LM orbited the Moon and then descended to the surface, an inability to maintain high-gain pointing would mean, among other things, that the crew would be unable to receive digital data from Earth at a high enough speed that it could be directly loaded into the LM computer. Although the landing could be flown by using the LM's omni-directional antennas for communications and telemetry, loss of the high-gain dictated a change in procedures.]

[Duke - "So we had to start changing (spacecraft) attitudes and we had to start getting the stuff (meaning the computer updates) up at low bit rate, and that led to a real problem loading the computer with the ephemeris and all of that. So we ended up having to copy a lot of that stuff (by hand). There was pages of it, I remember. And I just copied all of that stuff down and then had to manually put that in the computer."]

[The ephemeris is a table of data concerning spacecraft motions.]

[Duke - "Then, as we powered up the RCS (Reaction Control System, the small steering rockets), we had a double regulator failure in one of the systems."]

[The LM had four sets of four, small rocket engines used to rotate the spacecraft around three axes. There was a set of four RCS thrusters at each corner of the LM Ascent Stage. Because the RCS was so critical to the performance of the mission, it actually consisted of a pair of identical systems of tanks, valves, regulators, and piping. While Duke was manually updating the computer, Young opened valves which fed high-pressure helium into the RCS propellant tanks, thereby pressurizing them. As he did so, Young noted that the pressure in RCS System A climbed above the planned value of 184 psi and, indeed, continued to increase at approximately 10 psi/minute. (See sections 9.6.3 and 14.2.4 of the Apollo 16 Mission Report for details.) This observation indicated that there was a leak in the regulator assembly and, in order to reduce the tank pressure, Young transferred some of the RCS System A propellants to ascent propellant tanks and, by making several such transfers, was able to maintain the System A pressures at about 180 psi. Prior to the Powered Descent, Young had to perform several transfers in order to maintain the RCS pressure at the desired levels but, eventually system A was used for the landing.]

[Once the high-gain and RCS problems were resolved, Young and Duke undocked and moved the LM away from the Command Module Casper at 96 hours 14 minutes. They were near the low point in their orbit and planned to begin the descent on the next pass, two hours later. During this final orbit prior to PDI, Young and Duke would complete their preparations for the landing and Command Module Pilot Ken Mattingly would make a third SPS burn in order to put himself in a circular, 60-mile-high orbit in which he would perform three days of observations and from which, if necessary, he could maneuver to rendezvous with the LM in the event of an emergency lift-off.]

[Duke - "The big (CSM) problem came an hour before we were to land when Mattingly reported a problem in his spacecraft."]

[Like the LM Descent engine, the direction of thrust of the CSM SPS engine could be varied by rotation around a set of gimbals and, during a pre-ignition checkout of the SPS system, at about 97 hours 30 minutes, Ken Mattingly felt his spacecraft begin to shake when he checked the backup servo-mechanical system associated with the yaw axis. Details can be found in sections 9.6.4 and 14.1.10 of the Apollo 16 Mission Report and in Chapter 12 of Andrew Chaikin's A Man on the Moon. About a week before launch, the mission rules had been changed so that, if there were any problems in either the primary or backup SPS gimbal systems at this point in the mission, the circularization burn could not be performed and, therefore, this problem in the yaw backup system meant that the mission was in jeopardy.]

[Mattingly had discovered the problem while the two spacecraft were over the Lunar Farside and it was obvious to the crew that there would be no landing on this orbit. According to the Mission Report, "during pre-flight discussions, the flight controllers and the crew had agreed that, in the event of a 'no-go' for powered descent, a 'brute force' rendezvous would be executed when the LM and CSM were at their closest point of approach, approximately 2000 feet. The LM and CSM crews discussed execution of the join up, but decided not to expend CSM RCS propellant until ground personnel had an opportunity to assess the situation. The LM crew then turned to the section of the checklist which was the wave-off for powered descent and configured the systems for normal lunar orbit."]

[Once the two spacecraft were back in contact with Houston, two complete tests of the gimbal systems were performed so that engineers on the ground could evaluate the situation. Once the tests were complete, Houston requested that the crews perform the "brute force" rendezvous at their next closest approach at about 99 hours.]

["Duke - I thought we were going to abort. John and I were really sad. It looked like we weren't going to get to land; which is a bitter pill to swallow there, because, you could look down and, at perigee, it was (planned to be) eight miles above the landing site."]

[The "brute force" rendezvous was to have taken place at the high point in the orbit, over the lunar Farside. At the time, the Command Module was in the lead by about a half mile. In order to perform the rendezvous, Mattingly would fire the CSM RCS against his orbital motion and let the LM catch up with him. However, as Mattingly began the maneuver, Young became concerned about the effect the maneuver would have on relative position and speeds of the two spacecraft at the low point in their orbits and decided to terminate the rendezvous until further discussions could be held with the experts in Houston. Those discussions took place as soon as the two spacecraft had re-established communications with Earth and it was then decided to perform the rendezvous near the low point in the orbit when the two spacecraft were about 7000 feet apart. The rendezvous was performed at about 100 hours without incident.]

[For two hours, Houston considered the data and the options and, in the end, decided to proceed with the landing. As Ken Mattingly later told Andrew Chaikin, this is not the decision he would have made. Mattingly knew the spacecraft inside and out and, in hindsight, was aware that the margins of safety in this particular situation were slimmer than Houston thought. However, at the time, he was eager to see the mission continue and wasn't about to question this apparent act of boldness on Houston's part. (See Andrew Chaikin's A Man on the Moon for details.) At about 102 hours, Houston gave the crew of Apollo 16 a Go to perform the landing, with the descent now scheduled to begin at 104 hours, 17 minutes 25 seconds, three orbits and six hours late.]

[Duke - "When they gave us a Go, we were really excited! We were really pressed (for time) prior to (the original) undocking (because of the high-gain and RCS problems), but we got everything done. You know, we caught up, overcame our problems, undocked - and then Ken had his problem. And, while they looked at that, you know, we were just floating around, really. Just orbiting, after we got rendezvoused, waiting for them to decide what to do. Then, when we got to go - Jim Irwin had given us the Go - we were really excited, I remember. So we got ready for PDI."]

[One consequence of the landing delay was a postponement of the first EVA. Young and Duke had awakened at about 91:30 and had planned to perform a full, eight-hour EVA after landing. According to the original flight plan, they would have gotten to sleep at about 113 hours, at the end of a 21 1/2 hour day. In order to perform the EVA after the delayed landing, they were looking at a 27 1/2 hour day and, in Houston, Flight Director Gerry Griffin was unwilling to test the crew's endurance to that extent.]

[Duke - "They were beginning to say, 'You're going to be up 35 hours' or something like to the end of the EVA and maybe we ought think about sleeping first. We agreed to that, but it turned out I wish we hadn't. I wish we had gone on out and stuck to our timeline, because it required a lot of changes in the procedures once we landed. You know, we had to change all the checklists, change all the timelines. This was a big mess."]

[During the final minutes before receiving permission to perform the landing, Young and Duke made a final check of their switch and circuit breaker configurations, yawed the spacecraft 20 degrees to improve communications with Earth, activated RCS System A, activated the Digital Event Timer, aligned the Primary Guidance and Navigation System (PGNS) and the Abort Guidance System (AGS), and, five minutes before PDI, closed the landing radar circuit breaker to power it up.]

[Young, from the 1972 Technical Debrief - "As we were coming around the corner for PDI, we didn't have high-gain and our yawing was 20 degrees for the descent. Charlie says we're on the omnis and we couldn't get lockup for the state vector that we needed to do PDI. About 12 minutes prior to PDI, Charlie suggested that we roll (means yaw) right 20 degrees. We rolled (means yawed) right 20 degrees, and it improved the comm margins considerably. I think it's something that everybody who's going to work omnis should think about - putting the omni antenna toward Earth as best they can to get that update - because it was 12 minutes before we got that update. I figured we were almost in another wave-off situation. That was a good suggestion and we did PDI from it - off nominal. We did it from zero yaw all the way down."]

[Journal Contributor Roland Spetch writes, "Rotations about the three axes of a vhecile are known as roll, pitch, and yaw. In an airplane, roll is the rotation about the flight direction, pitch is the rotation about the wing axis, and yaw is the rotation about the vertical axis. Similarly for the LM crew, facing the hatch, roll is the rotation about an axis going from their backs through the hatch, pitch is the rotation about their left/right axis, and yaw is the rotation about the axis that runs up through the docking adapter."]

[Duke, from the 1972 Technical Debrief - "If you consider trimming RCS maneuvers in the LM, there's no question in the real world that the thing's maneuvering. You can tell what jets are firing. You can, in fact, hear the jets when you have your helmet off. At 2 degrees a second in the lunar module, you can feel the rotation rate. Like Ken said yesterday (in the portion of the Technical Debrief related to Command Module operations), I never felt the rotation rate in the Command Module, but in the LM at 2 degrees a second, you can sure feel it. And (there is) no question in your mind which way you're going and which jets came on."]

[Duke, from the 1972 Technical Debrief - "We had a pretty tough time with the high bit rate, due to the loss of (the) steerable antenna."]

[Young, from the 1972 Technical Debrief - "They weren't getting lockup coming around (to) the PDI. Man, I was really sweating that when you said 'roll, let's take the yaw out.' And we did it and they got lockup. That was a cool move. That put the omni antenna right at the Earth. That may have been just the margin we needed, 12 minutes prior to PDI. I thought we were in trouble then."]

[Duke, from the 1972 Technical Debrief - "Me, too. I thought it was really gone. The up-link was always clear, and we didn't have any garbled transmissions. So I had no trouble with the PADs."]

[A "PAD" (Preliminary Advisory Data in NASA-ese) is a set of data read up by the ground and entered by the crew on a pre-printed form. This data was used to update the computer and could be used in the event that communications with Houston was lost.]

[Duke, from the 1972 Technical Debrief - "The ground kept saying that we were really noisy - really horrible. So I used a louder voice. I know on Apollo 10 (when Charlie was CapCom and John was Command Module Pilot), we had a couple of revs of that and it's really miserable (as CapCom) trying to get things passed back and forth."]

[Young, from the 1972 Technical Debrief - "We sure did, didn't we, come to think of it."]

[Transmissions from the LM could be noisy because the LM antenna was small and there was not much broadcast power available. Transmissions from Earth to the LM were rarely noisy because there was virtually unlimited power available. Only poor pointing of the spacecraft antenna degraded transmissions from Earth.]

[During the 1972 Technical Debrief, John and Charlie then turned to the question of their original plan to perform PDI on the orbit immediately following undocking and then do an EVA immediately after landing.]

[Young, from the 1972 Technical Debrief - "If Ken had done the circ(ularization) burn, we wouldn't have had any trouble doing the PDI on that rev, so I think that the (pre-flight) decision to cut a rev out of the timeline was perfectly safe. It didn't work out (because of the CSM gimbal problem) and there may be other reasons why it wouldn't work out in the future; but, if you think positively, there's no reason the timeline itself doesn't constrain it to doing the PDI after the first rev."]

[Duke, from the 1972 Technical Debrief - "Even with all our communications problems, in doing the manual updates to P27, we got a little behind there. But, by the time we got to circ, we were caught up. And I agree with John. I think that the timeline was adequate and I recommend it for 17, if they plan to get out first."]

[The Apollo 17 crew followed this recommendation and began their powered descent 2 hours 22 minutes after separation from the Command Module. In comparison, on Apollo 15 the interval was 3 hours 51 minutes. The difference represents a considerable savings in LM consumables that could then be used for a longer stay on the surface.]

[Young, from the 1972 Technical Debrief - "One thing in favor of getting out first is you've already got your pressure suit on, and you don't have to go through all that Mickey Mouse again. Boy, I tell you, that taking that rascal on and off, you got what I consider the worst part of your prep already done. And I think that ought to be considered as a factor in this business."]

[One reason that John and Charlie were able to get ready to do PDI on the first rev after undocking is that they omitted a calibration of the Landing Point Designator (LPD). After pitchover, with LPD activated, John was able to click his handcontroller left, right, forward, or back to make a small, discrete change in the targeted landing point. Prior to PDI, he had planned to perform a test of the LPD calibration using the Crewman Optical Alignment Sight (COAS), - which was mounted in his window for use during rendezvous. During the test, John would have maneuvered the spacecraft so that the LPD was properly aligned with the CSM or some other object and then would have made sure that computer readouts were consistent.]

[Duke, from the 1972 Technical Debrief - "We didn't do the COAS calibration or the LPD calibration due to being behind, thanks to the comm problems on that first rev. As it turned out, everything was perfect."]

[Young, from the 1972 Technical Debrief - "Yes; and, as a matter of fact, for any reasonable rendezvous or any reasonable landing, the COAS calibration and the LPD calibration are just something to take up time in the timeline. Those things are done on the ground, and they're done perfectly adequately, based on our experience. And it costs you gas, too, because they're 2 degree-per-second maneuvers to get to them and they perturb the orbit."]


Detailed LM flight procedures can be found in the Apollo 16 LM Timeline Book they are about two-thirds of the way down the lefthand column on Page 6.


The mission review done with Charlie Duke does not start until 104:13:09.

The CapCom is Apollo 15 LMP Jim Irwin.


MP3 Audio Clip (11 min 54 sec)

104:01:42 Duke: Jim, could we yaw right a little bit and point that omni right at you? Would that help?

104:01:48 Irwin: Stand by.

[Comm Break]
104:03:07 Duke: Okay. Any words on that uplink, Jim?

104:03:10 Irwin: Why don't you put in that yaw maneuver; yaw right 20 degrees, that might help.

104:03:19 Duke: Roger. (Long Pause)

104:03:32 Young: Here's yaw right 20.

104:03:34 Irwin: Roger.

104:03:35 Duke: Okay. And how about reading that up to me, and I'll copy it down.

104:03:38 Irwin: Looks like we're getting good data now, Charlie. Stand by. We're uplinking now. (Long Pause)

104:04:25 Duke: Okay, Jim. I think we'll start the...John says we'll start the PDI from zero yaw since the omni is pointing right at you.

104:04:32 Young: (Would) that be better for you?

104:04:35 Irwin: Stand by. (Pause) Okay, Orion. We're finished with your computer. (Pause)

104:04:47 Young: Okay. (Long Pause)

104:05:19 Irwin: Okay, Orion. This is Houston. That zero yaw looks okay.

104:05:25 Duke: All right, fine. Thank you. (Very Long Pause)

[Comm Break]

[They have been transmitting in push-to-talk mode. They switch to voice-activated (VOX) and we hear Charlie midway thru a sentence.]

104:06:48 Duke: ... and call P63, John. How do you read us VOX, Jim?

104:06:52 Irwin: Loud and clear.

104:06:55 Young: Read loud and clear on VOX. Okay?

104:06:58 Irwin: Yes, sir, John. You're loud and clear. (Pause)

104:07:04 Young: Ten minutes.

104:07:07 Duke: Okay. Let's check the DPS configuration card. (Reading settings John will check) CB(11): Deca Gimbal AC, Closed.

104:07:13 Young: It's closed, and Deca Power's closed.

104:07:16 Duke: CB(16): Display/Engine Override Logic, Closed.

104:07:19 Young: It's in. Yeah, go.

104:07:20 Duke: Stab/Control, all closed except the AEA.

104:07:22 Young: All closed except the AEA.

104:07:24 Duke: Okay, 25 degrees a second.

104:07:26 Young: 25 degrees a second.

104:07:27 Duke: Throttle Control, Auto/Commander.

104:07:29 Young: Auto/Commander.

104:07:30 Duke: ATT/Translation of 4 Jets.

104:07:31 Young: 4 Jets. (John now reads settings Charlie will check) Balance Couple, On. Engine Gimbal, Enable. Descent Engine Command Override, Off.

104:07:35 Duke: Off. Go.

104:07:37 Young: Abort/Abort Stage, Reset. Dead Band, Min. Attitude Control. Three to Mode Control. PGNS/AGS, Auto.

[The Abort and Abort Stage buttons would have been used in the event of aborts using the descent engine or the ascent engine, respectively.]

[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 column), The Commander would check the position of the Guidance Switch and then push the appropriate button.

104:07:43 Duke: Go.

104:07:44 Young: Okay.

104:07:45 Duke: Pro.

104:07:46 Young: On Hi Mult, Landing Radar/Computer; Monitor the PGNS. PGNS, Guidance; AGS, Mode Select. Altitude/Altitude Rate. Supercrit Pressure, 1220; Ambient Pressure, 390.

104:08:00 Duke: Okay. (Pause)

104:08:12 Irwin: Orion, you can configure for normal RCS configuration now.

104:08:21 Young: Okay. System A is on.

104:08:23 Irwin: Roger.

104:08:32 Duke: Hey, Jim. We got an RCS A Reg light when that went on. The pressures are good, though.

104:08:36 Irwin: Roger. (Pause)

104:08 47 Duke: Okay, John. The DET is set. (Pause) Okay. FDAI. Verify the FDAI. 011... (Pause) (Garbled) it up a little bit. (Pause) Okay, Verb 40 Noun 20, please.

104:09:22 Young: Got it, Charlie.

104:09:23 Duke: Okay.

104:09:25 Young: (Garbled) (Pause)

104:09:34 Duke: AGS and PGNS are aligned. 410 is ... (Pause) ... Back to zero. 400 plus 1 going in. (Pause) And the needles deflect. (Pause) 433.

104:10:04 Duke: Amazing. How do you read, Jim?

104:10:06 Irwin: Loud and clear.

104:10:12 Duke: Okay.

104:10:13 Young: What happened?

104:10:23 Duke: Okay. We are clear down to 5 minutes. At 5, we close the Landing Radar breaker.

104:10:30 Young: Right. (Long Pause) Starting a little high (garbled). Based on the (garbled), it will probably be double at first (garbled). (Long Pause)

104:11:11 Duke: The old Earth is sure pretty.

104:11:17 Irwin: Orion, bring battery 3 on (line) at minus 5.

104:11:24 Duke: Roger; copy. (Pause) (Garbled) pull me right up under my - little (garbled).

104:11:50 Duke: Okay. 05:36, John. Everything looks great. (Pause) Hey, Casper. How do you read? Over. (Garbled).

104:12:10 Young: Okay. Five minutes, Landing Radar breaker is going closed.

104:12:16 Duke: Batt 3 is On.

104:12:17 Young: Altitude Transmitter is 3.4, almost; Velocity Transmitter is 3.82.

104:12:29 Irwin: Say again the reading on the velocity, John.

104:12:31 Young: (Not yet having heard Jim) Okay; Altitude Transmitter. (Answering Jim) 3.8.

104:12:39 Irwin: Roger. Copy 3.4 and 3.8.

104:12:44 Young: Correct. (Long Pause) MP3 Audio Clip (8 min 24 sec) 104:13:09 Irwin: Orion, you're Go for PDI.

104:13:14 Young: Roger, Go for PDI. (Pause) Okay. Pro for the final trim.

104:13:23 Duke: Pro. (Pause) Looks better than it did. Go ahead. Enter.

104:13:31 Young: Enter.

[Duke - "I'm probably talking about the attitude and all of the PGNS information."]

[Journal Contributor Frank O'Brien notes, "Right before the Powered Descent begins, the computer displays the desired attitude for the burn. By pressing the 'Pro' key on the DSKY, the crew is accepting the attitude and is allowing the computer to perform any necessary adjustments. Usually, the crew had already maneuvered the LM to exactly the desired attitude, so there was little need for the computer to trim the attitude."]

104:13:35 Duke: Go. My watch is set and wound. (Long Pause)

104:14:05 Young: It checks.

104:14:07 Duke: About a second off here.

[Jones - "I assume that you were using the watches as backups to the Digital Event Timer (DET) and that you were making sure that the DET and the watches were running at the same speed. Is that right?"]

[Duke - "Yeah. It was that Omega Speedmaster that we wore. It had a stopwatch on it; and, every time we had a major burn event like that, I would use the stopwatch as a backup to our event timer. During training, you'd forget to wind your watch; and you'd look down about halfway through the burn and the thing had stopped. They were just wind-up watches in those days; they weren't quartz or anything like that, so we had to make sure we wound them. So I made it a practice that, (chuckling) every time we got to a major event like that, I was going to make sure my watch was wound up."]

104:14:11 Duke: Okay. Stand by for 2 minutes, John.

104:14:15 Young: Roger. (Long Pause)

104:15:12 Young: Okay; good. (Pause)

104:15:16 Duke: Starting at about 10 (nautical) miles, it looks like. (Garbled)

[This is probably a reference to their altitude at PDI as projected by the Primary Guidance and Navigation System (PGNS). A nautical mile is about 6080 feet or 1853 meters. They had planned to start PDI at 50,000 feet or a bit over 8 nautical miles; but, as noted above, are actually going to start the descent at 66500 feet or 10.9 nautical miles. Note that Charlie is not being precise in his conversion of feet to nautical miles. Because they are starting high, during the initial phases of the burn, the computer will bring them down at a higher than normal rate until they are on the planned path.]

[Duke, from the 1972 Technical Debrief - "We started high and to the south, (at) about 16,000 feet high, as a matter of fact."]

[Young, from the 1972 Technical Debrief - "16,000 feet high?"]

[Duke, from the 1972 Technical Debrief - "Yes, we started (at) About 66,000 feet."]

[Young, from the 1972 Technical Debrief - "And we were about 16,000 feet to the south (of the planned descent track), also."]

[Duke, from the 1972 Technical Debrief - "Right after throttle down, we were back on standard (descent) profile."]

[Young, from the 1972 Technical Debrief - "Yes, it was really beautiful."]

104:15:24 Young: Okay, 2 minutes. Master Arm, On. (Pause)

104:15:29 Young: Two minutes; Master Arm's On. Two lights, Houston.

104:15:31 Irwin: Roger. Copy, two lights.

[The Master Arm switch provides power that will open the engine fuel valves. The two lights that have just come on - one for altitude and one for velocity - indicate that the radar is not yet receiving usable returns from the lunar surface.]
104:15:33 Duke: PGNS in Mode Select. 367 is in. Next thing is at 30 seconds, John. (To himself) Turn the (checklist) page. (Long Pause)
[O'Brien - "367 is an AGS memory address what shows the LM altitude rate."]
104:16:08 Duke: Hey, Jim. You want us to turn the ranging back on?

104:16:13 Irwin: Negative.

[Charlie is asking Houston if they want him to do Doppler ranging on the Command Module with the LM VHF system.]
104:16:16 Duke: Okay. We're in Voice Backup.

104:16:21 Irwin: Roger. (Long Pause)

104:16:38 Duke: 50 seconds. (Pause)

104:16:48 Duke: Okay. (Reading) At 30, we hit Engine Arm. 30 seconds, Engine Arm goes to Descent, then we ullage.

[Because they are in zero gravity, the helium and propellants in the tanks are mixed and, just prior to PDI, the computer will fire the RCS thrusters against the direction of motion. This acceleration will move the fuel to the engine-ward part of the tank and the helium in the other direction, thereby ensuring that, when the valves open, it will be propellant and not the inert helium that flows into the combustion chamber.]
104:16:56 Young: DSKY's blank.

104:16:58 Duke: Pro. Five (Pause)

104:17:00 Young: Okay.

104:17:01 Duke: Engine Arm, Descent.

104:17:02 Young: Arm is Descent. Altitude light and Velocity light.

104:17:05 Duke: Okay. If no ullage, plus-X.

104:17:07 Young: Okay. (Pause)

[John will perform a manual ullage burn in the event that the computer doesn't. The X-axis is the thrust axis and plus-X is the up direction.]
104:17:14 Duke: If no ignition, just Start Pushbutton if we get ullage.

104:17:19 Duke: Ullage...

104:17:20 Young: Auto ullage.

104:17:23 LM Crew: Pro. (Pause)

104:17:28 Duke: Okay. Engine Start.

104:17:29 Young: Engine Start. Descent Engine Command Override is on.

104:17:32 Duke: Stick your throttle in min.

104:17:35 Irwin: Roger. We copy.

104:17:36 Young: All right.

[O'Brien - "Descent Engine Command Override allowed the crew to use the Thrust/Translational Hand Controllers (TTHC) to directly override the computer-commanded throttle setting of the Descent Engine. This would be necessary if full manual control were desired over the Descent Engine thrust."]

[For the first 26 seconds of the burn, the engine will run at 10 percent thrust.]

[O'Brien - "The LM descent engine was gimbaled much like the SPS engine. One of the reasons for the 10% thrust at the beginning of powered descent was to allow the gimbal actuators to point the engine through the LM center of gravity. Once the initial gimbaling was done, the engine throttled up to 93%. The actuators were intentionally very slow (something like 0.2 degrees per second) and transients like fuel sloshing could happen too fast for them to compensate. The RCS system compensated for all this after throttle up. The LM ascent engine was not gimbaled."]

104:17:39 Duke: Descent Engine Command Override; Master Arm, Off.

104:17:42 Young: Master Arm is coming Off.

104:17:45 Duke: Stand by for throttle up; thrust-to-weight is okay.

104:17:49 Young: 22, 23, 24, 25, 26...

[Here, John is counting up to throttle up to 93 percent thrust at 26 seconds into the burn.]
104:17:53 LM Crew: Throttle up!

104:17:54 Young: On time!

104:17:55 Duke: Feel that beauty come on!

104:17:56 Irwin: Roger; we copy.

104:17:57 Duke: Okay, thrust-to-weight is good. (Pause) 66,000 feet. They (meaning the flight dynamics analysts in Houston) were right on. (Long Pause)

[They is a reference to Houston's pre-PDI predictions of the PDI altitude based on tracking data.]
104:18:18 Duke: We're looking at a minute. Hey, Jim; at pitchover, do you want me to go Aft omni or stay Forward?.

104:18:26 Irwin: Stay Forward and you've got a Go at 1 (minute into the burn).

104:18:31 Young: Roger.

104:18:32 Duke: Okay, we're way high, John; we got to get down. Way high on the H-dot.

[H-dot is the time derivative of height (H) or, in other words, their rate of descent.]
104:18:36 Young: All right. Just a minute, Charlie. Down to 45 already. (Long Pause)
[Their typical descent rate will be 116 feet per second and John may be saying that their descent rate has built up to 45 feet per second. John occasionally has trouble with his word choices and I am inclined to believe that he meant to say "down at 45, already".]
104:18:55 Duke: Systems look good. Passing 1:30 (minutes).

104:18:58 Irwin: Okay, Orion. I have a 169 for you...

104:19:00 Duke: Double H-dot, almost.

104:19:01 Young: Yep.

[That is, the descent rate is about twice the planned rate at this point in the descent as the computer moves them down to the planned trajectory.]
104:19:03 LM Crew: (To Irwin) Go ahead.

104:19:05 Irwin: Plus 00800.

[Jim's call of "169" refers to a change in the first register of Noun 69, which is the east/west component of any landing site correction. Charlie will enter 'plus 00800 into the computer to move their target point 800 feet downrange (west).]
104:19:12 Duke: Plus 00800. (Garbled) hundred feet. (Garbled)
[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 downlink to verify that the number was good. Noun 69 was one of the easiest opportunities for the crew to kill themselves."]
104:19:17 Irwin: And you've a Go for enter...

104:19:18 Duke: (Garbled)

104:19:20 Duke: Excuse me, John.

104:19:21 Young: Okay, that's entered. It's entered. (Pause)

104:19:27 Irwin: And you're Go at 2.

104:19:28 Duke: Passing two minutes.

104:19:30 Young: Really looking good.

104:19:31 Duke: Okay. We're going to have to yaw out here at 3. (Pause) Might take that out when we get (garbled).

[Charlie is probably saying that they will have to change the spacecraft yaw at 3 minutes.]
104:19:47 Duke: AGS and PGNS are tracking right on, Jim!

104:19:49 Irwin: Roger.

104:19:50 Duke: Within a tenth of a foot a second.

104:19:52 Irwin: Roger. (Long Pause)

[Charlie is comparing the two computers and they are giving nearly identical readings of the three velocity components.]
104:20:05 Duke: At 3 minutes, (I'll check) propellants. (Pause) Pressures are holding good in the DPS (Descent Propulsion System, pronounced "dips").

104:20:20 Young: (Garbled) oxidizer pressure looks good. (Pause)

104:20:24 Irwin: Orion, you're Go at 3.

104:20:26 Duke: 3.

104:20:27 Young: Roger; Go at 3.

104:20:31 Duke: I'll check the ED (Explosive Device) batteries one more time. (Pause)

[These are the batteries that would provide power to the small explosive charges that would separate the two LM stages in the event of an abort.]
104:20:41 Duke: And they're still 37 volts, Jim.

104:20:43 Irwin: Roger; we copy.

104:20:45 Young: Velocity light's out, Charlie.

104:20:46 Duke: Okay. Wrong transmitter, probably.

[They are beginning to get radar returns from the surface, much earlier than they had expected. They are now about 3:20 into the burn and, according to figure 7-2 in the Apollo 16 Mission Report, their altitude is about 57,000 feet.]
104:20:52 Duke: We got a (garbled). (Pause) Watch it now.

104:20:57 Duke: Locked on at (garbled) thousand (garbled) way.

104:20:59 Young: (You're) cutting out, Charlie.

104:21:02 Duke: I say, there's no way to get the Altitude light at this height. (Pause) (Four) minutes... (Pause)

MP3 Audio Clip (10 min 03 sec)

104:21:26 Irwin: Orion, you're Go at 4.

104:21:28 Duke: We're 50,000 (feet).

104:21:30 Young: Look at that! Altitude and Velocity lights are out at 50k!

[The landing radar is now getting good returns from the lunar surface.]
104:21:34 Duke: Isn't that amazing? Copy that, Houston?

104:21:38 Irwin: We copy.

[O'Brien - "Charlie's reaction to the unexpectedly good performance of the landing radar at 50,000 feet is well founded. The landing radar was designed to provide good altitude data below 25,000 feet, and velocity data below 18,000 feet. In previous missions, it locked on at about 40,000 feet."]
104:21:40 Young: Look at that data, Houston. When do you want to accept it?

104:21:48 Irwin: Okay, you have a Go to accept. (Pause)

104:21:56 Duke: Okay. It's in.

104:21:59 Irwin: Roger. (Long Pause)

[Jones - "When the lights are on, the radar is not getting returns from the surface. Is that right?"]

[Duke - "That's right. And as soon as those go out, you can incorporate that information into the computer."]

[Jones - "Is a light generally an indication of something that is not working?"]

[Duke - "Yeah."]

[Jones - "And when the light goes out, it's normal operation and you don't have to worry about it."]

[Duke - "Yeah. That's typical airplane...(Pause) When the lights go out, it means that the radar signal strength is reliable and then, at that point, we accepted it."]

[Jones - "So the computer didn't actually use the data until you told it it was okay."]

[Duke - "Yeah. And I've forgotten what you did to accept it, but then the computer started using it to update its trajectory."]

[O'Brien - "A Verb 57 was entered on the DSKY to tell the computer to begin accepting radar data."]

104:22:19 Duke: AGS and PGNS will be getting off a little bit in altitude now. Update.
[The PGNS uses data from both the LM inertial platform and the radar to update its knowledge of the spacecraft location and velocities while the AGS uses only data from a set of "strap-on" gyros. Now that the PGNS has radar data, it will revise its altitude estimates. Figure 7-3 in the Apollo 15 Mission Report shows the effect that acceptance of the radar data had on the PGNS altitude estimates during the descent that Dave Scott and Jim Irwin flew.]

[Jones - "What was your attitude towards the AGS. It was primarily designed as an abort..."]

[Duke - "We had a lot of confidence in it. It worked real good. We had some good rendezvous in training with the AGS. I was positive it could get us back to orbit if we lost the PGNS on descent."]

[Jones - "Gene and Jack said that, if the PGNS had failed during the final stages of descent, they had confidence in the AGS to actually go in with it and land."]

[Duke - "Yeah. I think you could land with it; it was good enough on the attitude control. As far as holding attitudes and stuff like that, you could fly it. Of course, to me, you would have to descend a little bit slower without your radar ranging and stuff like that. Without landing radar information, I think it would have been a little bit difficult to tell exactly how high you were above the Moon. The dust and the shadow was probably the two primary indicators of getting close. But I was glad we had landing radar, because it looked like to me, a couple of times, we were higher than we were; but the landing radar was giving us good information. And the dust...On previous missions, they picked up dust a little bit earlier than we did, apparently. So I had that mindset: that the dust was going to come in (at) 80-90 feet when it really didn't. As I look back at the videos and listen to the audio that was supposed to be synched to that - on the 16mm camera - the dust started a lot later than I had expected."]

104:22:28 Duke: At 5 minutes. Coming in like gangbusters.

104:22:32 Irwin: Orion, you're Go at 5.

104:22:39 Young: Roger. (Pause)

104:22:51 Duke: 39,000. Hey, look at that. 136 feet difference now. (Garbled) radar.

[This may be the difference in estimated altitude between the PGNS and AGS. I originally thought this might be a difference between the actual descent rate and the planned rate, but now do not believe that because of the following argument. The altitude difference at 104:15:16 was 16,000 feet and, as Charlie indicates in a moment, that difference has been closed in about 5 minutes. On average, then, they have descended about 50 feet per second more than they would have had they done PDI at 50,000 feet; and, consequently, the "136 feet difference" cannot be a descent rate difference.]
RealAudio Clip ( 22 minutes 16 seconds )

104:23:06 Irwin: AGS is tracking about 1000 (feet) high.

104:23:10 Young: Rog. We'll get there.

104:23:14 Duke: Six minutes, we should be at 32,000 (garbled).

[Charlie is consulting a table on page 7 ( 442k in the Apollo 16 LM Timeline book.]
104:23:16 Young: 35 (thousand feet altitude).

104:23:16 Duke: Not quite back on profile, but almost.

104:23:17 Young: (Garbled)

104:23:24 Irwin: Orion, you're Go at 6.

104:23:26 Duke: 45 percent (fuel remaining). Right on.

104:23:27 Young: Roger.

[Journal Contributor Paul Fjeld - "Up on the CDR's main panel beside the timers were two small digital EL (Electro-Luminescent) displays that showed fuel and oxidizer percent remaining. The crew could monitor either set of tanks by pushing the PRPLNT QTY MON switch to DES 1 or DES 2 depending on which was more conservative (Houston would make the call). The LMP would just look over and call out the lowest number." Here, Charlie is also comparing the readout with a chart of expected values.]
104:23:28 Duke: Right on. (Long Pause) Okay. At 6:30, should be at 30,000.

104:23:58 Duke: Mark it, 32,000. Looking pretty. Okay. Looking good, John. (Pause) Sun angle's getting down there.

[Jones - "What do you mean by 'sun angle's getting down there'?"]

[Duke - "We're gaining shadow. We're going into sunset. Toward the terminator. As you approach the terminator, the shadows get longer and longer and longer."]

[This statement suggests that Charlie was able to see some of the lunar surface north of their ground track. Note that, when he says 'sunset', he means that, from their perspective in the LM, traveling west, the Sun is about to set. At the landing site, it is actually early morning and, from a ground-based perspective, the LM is approaching the sunrise terminator.]

104:24:15 Irwin: Throttle down (will be at) 7 plus 23.
[At 7:23, the computer will cut the throttle setting to 55 percent.]
104:24:16 Duke: AGS and PGNS H-Dot are right on.
[H-dot is the time derivative of height and, therefore, is the descent rate.]
104:24:20 Duke: (Garbled)

104:24:22 Young: (To Irwin) Understand, 7:23.

104:24:23 Irwin: Roger. (Pause) And you're Go at 7.

104:24:27 Duke: Seven minutes. Mark it. Seven minutes. (Responding to Irwin) Rog, go. 104 (feet per second) down, 28,000 (feet) altitude. (The AGS is) still about 1000 (feet) high, looks like.

104:24:37 Young: Well, it's starting to look pretty good.

104:24:39 Duke: Yeah. 223. Setting up ready...(Getting his tongue untied) (Getting) the AGS ready (for an update) at 14k. Then I do a 360 and then turn the (16mm movie) camera on. (Circuit) breaker is in.

[In common American usage, "doing a 360" means turning a complete circle. That meaning doesn't make sense in this context (unless he's joking), if for no other reason than the fact that Charlie would have gotten wrapped up in his hoses!]

[Duke - "(Looking at page 7 in the LM timeline book) We're setting up the AGS. That 223 is an entry into the AGS. You got it ready to go, but you Entered it at 14,000 feet."]

[O'Brien - "The '223' entry is simply a manual altitude update to the AGS. In this case, Charlie recognizes that a significant update is necessary. He has keyed in an update telling the AGS that it is at 14,000 feet, but has not yet pressed the 'Enter' key, which is necessary to send the command to the computer. He will press Enter at 104:26:16, as Orion passes thru 14,000 feet."]

[Duke - "And the 360 is another AGS entry."]

[O'Brien - "(AGS entry) 360 displays the LM X-axis velocity (parallel with the descent engine). From this display, Charlie sees the descent rate is 172 feet per second down. 367 is a related entry, which is the altitude rate (H-dot) of the LM."]

[Jones - "After you do the 360, then you start the sequence camera."]

[Duke - "You do a Noun 69, Enter, you do a 223, Enter at 14k, then a 360, Enter, then a sequence camera, on."]

[O'Brien - "Noun 69 displays LM velocities relative to the landing site in all three axis."]

104:24:54 Young: Throttle down. Right on time.

104:25:00 Irwin: Roger.

104:25:01 Duke: It was right on time, wasn't it?

104:25:03 Young: Yep.

104:25:05 Duke: How are you reading, Jim?

104:25:07 Irwin: Loud and clear.

104:25:11 Duke: Okay. You were clipping a little bit, John.

104:25:13 Young: Okay. (Pause)

104:25:22 Duke: 21,000 (feet) Coming up on 8 minutes.

104:25:25 Irwin: Orion, you're Go at 8.

104:25:27 Young: I can see the landing site from here, Charlie.

104:25:28 Duke: Amazing. Okay. Go at 8. John's got a visual.

104:25:33 Irwin: We copy.

[Figure 10-1 from the Apollo 16 Mission Report shows John's heart rate during the landing. During the initial phases of the descent, his heart-rate was only in the low 70s but, now that he can see the landing site, we can see his level of excitement increase. His peak rate of about 105 comes at pitchover. At touchdown, his heart rate will be about 90 beats per minute. For comparison, Neil Armstrong's peak rate was 150 and occurred at touchdown. Alan Shepard's peak was 100 at touchdown; Dave Scott's was about 98 at touchdown; and Gene Cernan's was 95 at touchdown. Because Pete Conrad experienced bothersome skin irritation under the sensors during the first few days of Apollo 12, he removed the sensor and tried to re-apply it, but later removed it entirely. We have no data on his heart-rate during the descent.]
104:25:34 Duke: 130 (feet per second descent rate). We're right on, John. Right back on profile. (Long Pause) How does it (meaning the targeting) look, to you?

104:25:50 Young: We're right in there.

[The following is taken from the Apollo 16 Mission Report. "At 20,000 feet, based on a pre-mission study which indicated the possibility of viewing the landing site prior to pitchover, the Commander put his eye near the COAS position and he was able to see nearly parallel to the minus-X axis (that is, out the bottom of the window past the descent engine). The western edge of Stone Mountain and South Ray Crater were clearly visible. It was apparent from the early view that the Lunar Module was targeted nearly perfectly into the landing site ellipse."]
104:25:52 Duke: Okay, standing by to update the AGS. Had a little roll steering here.

104:25:59 Irwin: Monitor Descent 1.

104:26:03 Young: Roger. Descent 1. (Pause)

[There are two propellant monitoring systems.]

[Jones - "When they say 'monitor descent 1', is that the conservative choice or is it the one they think is more accurate?"]

[Duke - "It's the one that's the lowest. It would be the conservative choice."]

Landing Movie by Gary Neff (4 min 55 sec; 8.6 Mb)

104:26:09 Duke: Okay, Jim. We got about a 3-degree roll command in.

104:26:12 Irwin: Roger.

104:26:16 Duke: Okay. Enter, 360, minus 0172, 0 Enter, 367 is coming up, and I'm starting the clock...(correcting himself) I mean the (16-mm movie) camera.

104:26:29 Irwin: Go at 9.

[As the descent continues, the spacecraft is slowly tilting toward the upright position. At pitchover, there will be a large change in the spacecraft orientation and John will get his first clear view of the landing site. However, as he mentioned in the Mission Report, "At approximately 14,000 feet, the entire landing site - Flag, Spook, and Double Spot Craters - became visible to the Commander."]
104:26:30 Duke: Okay. We're out of 12,000, John. Go at 9. Coming down at 182 (feet per second), a little steep. (Pause) Okay, we're going to be right on. It's just about right on, maybe 10 feet (feet per second off). 10,000 feet. Stand by. Okay, P64, at 8200. Pro.

104:26:55 Young: Pitchover.

104:26:56 Duke: Pitchover. Hey, there it is. Gator, Lone Star. Right on!

[According to the Mission Report, pitchover occurred at 7200 feet. Charlie is looking to the right (north) of the flight path. In the 16-mm film, Gator is the large crater at the bottom of the window and Lone Star is the small, sharp-rimmed crater on the eastern, outer flank of Gator. The next large crater beyond Gator is Palmetto. The large crater beyond Palmetto at the righthand edge of the window is Kiva.]

[Young, from the Mission Report - "At pitchover, you could see - just like pre-flight (simulations) Gator, Palmetto, and Spook, and the inverted, deep shadow pattern through Stubby, Wreck, Trap, Eden Valley, and Cove, right into Spook - although, at 15-degrees Sun angle, it wasn't as apparent (as in the simulations)."]

[Had they landed on time, six hours earlier, the Sun would have been 12 degrees above the local horizon, rather than 15. John's view is to the left (south) of the flight path although, evidently, he could see far enough north to have Gator and Palmetto in view at pitchover.]

[Young, from the Mission Report - "Of course, we had already seen the landing site on two other occasions when we were flying over it - because of the three rev slip. There's just no doubt in your mind when you're at pitchover, and the first thing you see was South Ray. There was some question about whether we'd see the ray patterns (out of South Ray) at the low Sun angle, but there's no doubt that we were seeing the ray patterns from South Ray at pitchover; and there's no doubt, at least in my mind, as to where the machine was flying to. And it was a simple matter to redesignate and back up a hair."]

104:27:00 Young: Call me the things, Charlie.
[The window in front of John is scribed with two sets of vertical and horizontal scales, one on the inside and one on the outside. If he stands so that the two sets of scales are lined up, once Charlie gives him a number from the computer, he can then find the point where the computer thinks they are going to land. This number - called the Landing Point Designator (LPD) angle - marks the position of the computer's target on the vertical scale. If John wants to move the target, he clicks the handcontroller left or right, forward or aft.] [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.]

104:27:01 Duke: Okay. 40...38 degrees.

104:27:02 Young: Okay.

[Young, from the Apollo 16 Mission Report - "After pitchover, a comparison of the Landing Point Designator with the computer and the movement of the vehicle showed that, if no further trajectory corrections were made, the Lunar Module would land approximately 600 meters north and 400 meters west of the center of the landing ellipse. Therefore, between altitudes of 3000 and 4000 feet, an estimated total of five redesignations to the south were made. The vehicle responded properly."]

[Young, from the 1972 Technical Debrief - "I think the LPD was perfect. I don't have any gripes there whatsoever. When we pitched over, we were north and long and you could see that. I was just letting the LM float in there until I could see where it was going. I took out the north because, according to our pre-flight maps, the north country was a little rougher. There were more (map) contour lines up north and down south; so we took those out and, when we got in close, we backed up a little and put in some rear updates. I don't remember how many there were."]

[When John said "so we took those out", he meant that he corrected the targeting so that he wouldn't be either north of the target or long. See John's commentary after 104:27:20.]

104:27:03 Duke: (Looking out his window to the north) Palmetto and Dot; North Ray.

104:27:06 Young: Okay.

104:27:08 Duke: Looks like we're going to be able to make it, John. There's not too many blocks up there.

[Charlie was the only LMP who made detailed comments on the landing site at pitchover. Others glanced out, but made no comments. The LMP's main job was to watch the computer and provide the Commander with LPD readings and values of altitude, descent rate, and forward velocity. Frank O'Brien plausibly suggests that, when Ed Mitchell glanced out his window to check the LM's position relative to Cone Crater, he may have also been checking out traverses to the crater rim. In both cases, the LMP could see important areas to the north that were hidden from the Commander's view by LM structure.]

[Duke, from the 1972 Technical Debrief - "We'd agreed (pre-flight) that I was going to look out since I had two good craters on my side (Palmetto and Dot); and it looked just like the L&A."]

[Readers should note that Dot Crater is named for Charlie's wife Dotty. It is a small, bright, sharp-rimmed crater, not unlike the charming Mrs. Duke.]

[The L&A was a model of the landing site which provided a view of the landing site which was shown in the windows of the LM simulator. The L&A was ceiling mounted and, on the floor, a television camera was moved in response to the simulated LM motions. The accompanying photo was provided by Frank O'Brien and shows the L&A to the left of the LM simulator.]

[Jones - "Did you get the L&A fairly early in the training cycle?"]

[Duke - "We had it about six months, total. You know we delayed a month. They delayed us to April. We were originally supposed to go in March; and then they had a problem with the RCS on the Command Module. I forget what that was but, anyway, it gave us another month for training, so if I remember right, we had about 6 months with the L&A. And it was real accurate."]

[Jones - "Did you guys ever get in the simulator and use the L&A to fly around the landing site at low altitude."]

[Duke - "Yeah, we did. And that was real helpful. We'd just fill up the gas and just fly around. The problem with the L&A was the maps. You know, the maps were only 15 meter resolution and, so, there was nothing on the L&A that was below the 15-meter resolution. So, when you got down close, you started seeing these, you know, these little ridges and contours that weren't visible on the maps. But just the general overview of the area was good. And that's why we recognized everything when we made pitchover."]

[Jones - "And you were fairly equatorial, so there would have been good, high-resolution Lunar Orbiter coverage of this site."]

[Duke - "I don't think we had Lunar Orbiter (photos)...I'm not sure where they got it from. I was always under the impression that they got the maps from Apollo 14. (True.) (Stu) Roosa (the Apollo 14 CMP) came over our landing sight and he took a lot of pictures of our landing site. So most of our stuff, I believe, came from that (Apollo 14 coverage)."]

[Charlie's quick look out to the north served a dual purpose. First, it gave him a chance to check their position so that, if they were off target, he could tell John. Second, it gave him a chance to see if they would be able to drive to North Ray Crater on EVA-3.]

[Duke - "There was a lot of speculation among the geological community, based on our (pre-flight) photographs, that we were going to have a rough road to go once we got up near North Ray Crater - that we might not be able to get up to the rim. But at pitchover, you know, I just looked out to the right to see what it looked like, 'cause John couldn't see it from his side. And it looked real good. Plus, I'd had a dream about some tracks being up that way and, out of curiosity, (laughing) I was checking to see if I could see the tracks."]

[Jones - "You talk about that in your book, Moonwalker, (on pages 199-200): that you came across some Rover tracks on the drive to North Ray, followed them, and found a Rover with two dead astronauts on it. They looked like you and John, but they'd been there for thousands of years."]

[Duke - "Yeah. But we didn't see any tracks, of course. But it was real real in the dream - this set of tracks."]

["It was up there on that valley floor after you pass Palmetto going up towards North Ray. There was a big low area, real smooth, and then, from there on, it climbed back up to North Ray. And we were expecting that it would be blocky up there, but it wasn't. We could see it all; and there were no tracks and no blocks; so we were going to be able to make it."]

[Jones - "Was there also some descent-specific reason for you to be looking out the window? In most cases, the LMPs were glued to the computer during the final phase."]

[Duke - "Well, I was, after this initial look. I wanted to help John...John and I trained that way. That I was going to help him verify where we were. The thought was, you know, if we were off, maybe two eyes looking out to figure out exactly where we were. But at pitchover there, of course, we recognized the craters. Palmetto, Dot, North Ray I recognized. And then I just started looking up there because we'd had such a big problem with our discussions with our geologists about making it to North Ray. They were concerned about it because the photographs showed a lot of blocks up there on that mountain up to the north of North Ray. So I just wanted to make sure we could do it."]

["John got on me a little bit, and said 'give me the numbers', you see. 'Call me the things, Charlie'. So, I was out of the cockpit (meaning, looking outside) there, then I got back in the cockpit (that is, focusing attention on the computer) (and) gave him the numbers, then I looked out again and that's where I told him we could make it. From then on, I was mostly in the cockpit."]

[Jones - "So you had about a five-second scan up to the north..."]

[Duke - "Yeah."]

104:27:12 Irwin: Orion, you're Go for landing.

104:27:16 Duke: Okay, 4000 feet,...

104:27:17 Young: (Acknowledging Irwin) Okay. Go for landing.

104:27:19 Duke: ...42 LPD. Okay, 3900 feet.

104:27:20 Young: Okay. Two (LPD clicks) to the south, Charlie.

[John has just moved the landing target two clicks to the south. As mentioned previously, he made approximately five redesignations between 3000 and 4000 feet. A bit later, an estimated five additional redesignations were made as the Lunar Module was approaching Double Spot Crater. According to the Mission Report, the net result of these redesignations was to move the landing site uprange (east) 620 feet (189 m) and south 635 feet (194m). Because the effect of a redesignation made at a higher altitude is greater than one made at a lower altitude, the five corrections made between 3000 and 4000 feet had the greatest effect.]

[Young, from the Apollo 16 Mission Report - "It was clear that the vehicle was going to be north and west of the pre-mission designated landing spot - 75 meters north of Double Spot Craters. However, there was no major attempt to land at the pre-mission designated spot, nor had there been any intent to do so prior to the flight because the surface traverse capabilities of the Lunar Rover negated the requirement to land precisely at the designated landing spot."]

104:27:26 Duke: Okay. It's in. Okay, 42...41 LPD. 3000 feet (and we're) on profile.

104:27:31 Young: Okay. There's...We're coming right down. It's going to be a little past (garbled).

104:27:39 Duke: 41 LPD.

104:27:42 Young: Okay. A little more to the left (south).

104:27:43 Duke: 2000 feet; 60 (feet per second [fps] descent rate). On profile.

104:27:44 Young: Okay. (Pause)

104:27:51 Duke: Okay, 42 LPD. Couple of more in. (Pause)

[Charlie can see the computer accepting John's target redesignations. As Frank O'Brien notes, "In a moment, we see the LPD go from 42 to 44 to 54 - meaning a shorter, steeper descent - so we know John redesignated the landing uprange (east)."]
104:27:56 Duke: 1400 feet, 44 (fps) down. Looking good. Okay, out of a 1000 feet. Right on profile. 54 LPD; dropping out the bottom now. 800 feet, 30 down.

104:28:13 Young: Okay, Houston. We're going to be just a little long...

104:28:15 Irwin: Roger.

104:28:16 Young: ...but we're just now abeam of Double Spot.

104:28:22 Irwin: Copy.

104:28:24 Duke: Okay, 23 (fps down). 22 down at 500 feet.

104:28:25 Young: Okay.

104:28:29 Duke: Some big blocks over here to the left, John. (Pause) Okay, 300 feet, 15 down.

104:28:33 Young: Okay. Okay. (I'm going to) take over, Charlie.

[Here, John is switching to manual control and no longer needs the LPD angles from Charlie. Now he needs altitude, vertical velocity and horizontal velocity.]

[Young, from the 1972 Technical Debrief - "It was working so well I was tempted to let it (the PGNS) do the thing all by itself; but the trouble is, we got down low and I could see that we were going to land in that pothole down there."]

[The 'pothole' in question is a shallow, 15-meter crater. John will overfly it and land with his rear foot pad about 3 meters beyond the west rim of the crater.]

[Young, from the 1972 Technical Debrief - "We took over, I guess at about 300 feet, and pitched forward a little, and we could see the surface all the way to the ground. Right close in there, out my window, I could see that crater down there, so I went forward a little bit and landed."]

104:28:39 Duke: Okay. (Pause) Okay, fuel is good: 10 percent. There comes the (LM) shadow.
[Journal Contributor Paul Fjeld - "Up on the CDR's main panel beside the timers were two small digital EL (Electro-Luminescent) displays that showed fuel and oxidizer percent remaining. The crew could monitor either set of tanks by pushing the PRPLNT QTY MON switch to DES 1 or DES 2 depending on which was more conservative (Houston would make the call). The LMP would just look over and call out the lowest number."]

[According to the Mission Report, "At about 450 feet altitude, the Lunar Module Pilot observed the Lunar Module's shadow from his window. At an altitude below 200 feet, as the Commander yawed the vehicle toward the right (that is, rotated right around the now-vertical thrust axis), he also noticed the shadow."]

[Young, from the 1972 Technical Debrief - "When we redesignated to the south, we must have had 30 degrees of (left) yaw and took it back out. At that Sun angle, we could see the rocks (through the dust) all the way to the ground and I think that was a great help. From 200 feet down, I never looked in the cockpit. It was just like flying the LLTV (Lunar Landing Training Vehicle); your reference is to the ground outside. You had another thing that nobody has ever remarked about before, and that was the shadow. I really didn't have any doubt in my mind how far above the ground we were with that shadow coming down (that is, getting closer to them as they approach the surface). I had no scale of reference to the holes; but, with the shadow out there in front of you and coming down, it really takes all of the guesswork out of it. For that kind of Sun angle, if the radar had crumped, I don't think you'd have had a bit of trouble in just going right in and landing just like a helicopter. First, we could see the thing (rocks and other surface features) all the way to the ground; second, the shadow was right there to help you with the rate of descent. When Charlie says 'you stopped and you're hovering', there wasn't any doubt in my mind that I was hovering. I could look out the window and see that we're hovering just like a helicopter. We were well into the dust - maybe 40 or 50 feet off the ground - when we were doing that."]

104:28:45 Duke: Okay, 200 feet, 11 (fps) down. Give me a couple of clicks up.
[Here, Charlie wants John to slow the descent.]

[Duke - "He's going down too fast. Okay? And our profile calls for 5 foot per second, H-dot; and he's 11. And 12 was our maximum. And, so, I wanted him to slow down a little bit. We were sinking too fast. I wanted to get him closer back to profile."]

104:28:52 Duke: Okay, 5 down at 130 feet, 2 forward.

104:28:54 Young: Okay. (Pause)

104:28:59 Duke: (Garbled). Drifting. Okay, looking good. Perfect place over here, John, a couple of big boulders. Not too bad.

104:29:08 Duke: Okay, 80 feet, down at 3. Looking super. There's dust. (Pause) Okay, down at 3. 50 feet, down at 4. Give me one click up. You're backing up slightly. (Pause)

104:29:22 Duke: Okay, 2 down. Stand by for contact. Come on, let her down. You leveled off. (Pause) Let her on down. Okay, 7...(correcting himself) 6 percent (fuel remaining). Plenty fat.

[Duke - "You can watch the 16-mm; and we just stopped. And then he gave me a couple of clicks down and we were in good shape."]

[Young, from the 1972 Technical Debrief - "We did hover for a short period of time, there, at about 40 feet off the ground, and the rates (meaning the three velocity components) were practically zero and there was blowing dust."]

[Duke, from the 1972 Technical Debrief - "It started at about 80 feet, John."]

[Young, from the 1972 Technical Debrief - "Yes, 80 feet. Certainly it started there and it got a lot worse, but you could still see the rocks all the way to the ground. The surface features - even the craters - which really surprised me. I was expecting two things: either the dust would be so bad (as on Apollo 12) we couldn't see anything, or there probably wouldn't be as much dust as there was. Possibly, it's the 15-degree sun angle that did all that. Because there's certainly plenty of dust down there to blow, and there's nothing thin about that regolith around the LM."]

[Because of the six-hour landing delay, the Sun was about 3 degrees higher than it was at the planned landing time and John is speculating that the change in lighting made it easier to see through the dust.]

[Jones - "Had you ever done any carrier operations?"]

[Duke - "No. Well, as a passenger I've landed on a carrier a few times, but never as a pilot."]

[Jones - "I ask everybody this question. Was it luck of the draw or something to do with carrier training that five of the six Commanders were Navy trained."]

[Duke - "I think it was the luck of the draw - just the fact that the guys in the second and the third group of astronauts that were still around were Navy. Most of them. Of course, Dave Scott wasn't. It just turned out that way, I think. For instance, if you look at those groups, Borman had left and Ed White had been killed and Gus Grissom had been killed...And they were Air Force, you see. Stafford had flown on Apollo 10 but, about that time, they were announcing the Russian mission (Apollo Soyuz) and he decided he wanted to go work on that. Jim McDivitt was in management at that point. McDivitt was actually Apollo Program Manager at the time we flew. So, it was just the way people's careers were going and their desires; and it just turned out the Navy guys stayed around."]

[Duke, from the 1972 Technical Debrief - "When the computer said (we'd) leveled off...there was no question in your mind that you'd stopped coming down."]

104:29:36 Duke: Contact! Stop. (Pause while they drop to the surface) Boom. (Static)
[Young, from the 1972 Technical Debrief - "When we got the Contact light, I counted the 'one-potato' and shut the engine down. The thing fell out of the sky the last 3 feet. I know it did. I don't know how much we were coming down, maybe a foot a second."]

[Duke, from the 1972 Technical Debrief - "I don't remember exactly, but about 1.8 (fps) - I think I saw - right before touchdown."]

[Young, from the 1972 Technical Debrief - "I wouldn't (want to) stroke that gear (by shutting down the engine earlier), man. I'll tell you, that would really jar your teeth."]

[According the the Apollo 16 Mission Report, Table 3-I, the landing (Contact) ocurred at 104:29:35, which was 02:23:35 GMT/UTC on 21 April 1972.]

104:29:40 Duke: Pro. Engine Arm. (Pause) Wow!!! (Garbled) man! Look at that!

104:29:43 Young: Pro. Engine Arm. Descent Engine Command Override.

104:29:46 Duke: Okay, 413. It's in. Check the APS (Ascent Propulsion System).

[Now that they are down, they will prepare to leave immediately, just in case there was damage to the spacecraft at contact.]
104:29:52 Young: Well, we don't have to walk far to pick up rocks, Houston. We're among them!

104:29:57 Duke: Open, close, open, close.

[Charlie is recycling a set of RCS propellant isolation or shut-off valves called Parker valves. They were made by a U.S. unit of Parker-Hannifin PLC.]

[Frank O'Brien - "The valve controls are on the main LMP switch panel. Each quad (that is, each of the four sets of RCS jets) is connected to two RCS systems. There are eight switches, two for each RCS quad, and have open and close settings."]

104:30:00 Duke: Old Orion is finally here, Houston. Fantastic!

104:30:12 Irwin: Sounds great.

104:30:13 Young: I can look right out to the left and see...

104:30:15 Irwin: Let's go Aft omni, Orion.

104:30:19 Young: ...Double Spot. And we're about...

104:30:21 Duke: (Responding to Irwin; the comm improves dramatically) Okay, you got it.

104:30:22 Irwin: That's better.

104:30:23 Young: Okay. We're forward and to the north of Double Spot. I would guess about 200 meters to the north and maybe 150 meters to the west. (Pause)

[This would put them about 250 meters north west of the planned landing site. Post-mission analysis indicates they are 210 meters north and 60 meters west of the planned landing spot. On the "Descartes EVA-I, III Part 2 of 2" map ( 0.6 Mb or 2.5 Mb ), the planned landing site is at CA.0/81.0 and they are actually near CB.1/80.6 or 8.9913 south latitude and 15.5144 degrees east longitude. A discussion of landing site coordinates is linked here.]
104:30:40 Young: It's not flatlands, though, Houston.

104:30:42 Irwin: Roger. I copy 200 meters north...

104:30:43 Duke: (Garbled) attitude is super, though.

104:30:44 Irwin: ...of Double Spot and about 150 meters west.

[Young, from the 1972 Technical Debrief - "I counted 'one-potato' after we got the Contact light and shut the engine down. Even so, I think we fell about three feet. I think we were very fortunate that the landing was so flat, because I really couldn't judge the slopes. We just lucked into almost zero roll (that is, north/south tilt), a couple of degrees - or 3 degrees - pitchup (that is, backward tilt); and, of course, we'd taken the yaw out."]

[Young, from the 1972 Technical Debrief - "I couldn't judge slope out the window worth a hoot, and that's the truth. Even down low. The ground looks flat, but I'm sure it would look flat if it had been a 6- to 8-degree slope, too. I don't see any way around that. I've done a lot of helicopter flying - looking at slopes - and you can't judge slopes in a helicopter from 100 feet on down very well, either. But I don't think you'd be in any trouble if you touched down within 10 or 15 degrees of being straight up and down. It's going to bother you some in deploying gear off the Lunar Module, but it isn't going to bother your performance."]

[According to the Mission Report, "Inspection of the region during extravehicular activity (EVA) indicated that, had the LM landed 25 meters in any direction from the actual site, it could have been on a local slope of 6 to 10 degrees."]

[Young, from the 1972 Technical Debrief - "The landing site orientation was about as flat as you can get. Like I said, 'It's more luck than skill' (Laughter) I hate to admit it, but it's true. Twenty-five meters either way and we would have been on a 10-degree slope."]

[Duke, from the 1972 Technical Debrief - "It's like landing on a carrier."]

[Young, from the 1972 Technical Debrief - "Add 15 meters to that (25 meters in any direction), and we would have been in a hole."]

104:30:46 Young: Man, I could see the...all the way to the ground. Just like flying the LLTV. Piece of cake.
[The LLTV is an open-framework test vehicle used by the Commanders to train for the LM landing. The LLTV was equipped with a downward-pointing jet engine that had the effect of removing 5/6ths of Earth gravity so that it would fly more or less like the LM. All the Commanders spoke highly of the LLTV and readers may wish to see the following detailed descriptions and comments: Neil Armstrong at 102:46:23 in the Apollo 11 landing chapter; Pete Conrad at 110:33:56 in Apollo 12; Dave Scott at 104:42:48 in Apollo 15; and Gene Cernan at 112:59:25 and 113:43:49 in Apollo 17. See, also, the LLTV Flight Rules.]
104:30:58 Duke: (To himself, checking a gauge) That's good. Ascent pressures look good. Okay, Ascent Helium Monitor, cycle; I did. O2 Ascent...

104:31:05 Young: (Garbled)

104:31:06 Duke: (Garbled) Fantastic!! Percy Precision (meaning John) has planted one on the plains of Descartes! (Pause) Camera Stop.

[Jones - "I think you may have been the most excited person, at least on tape, of the twelve who set down on the surface."]

[Duke - "I don't know about that (comparison); but I'll tell you, John and I - both - were so excited and exuberant. And the way we had trained and the way we were friends, we just talked about it. We just expressed our emotions, both of us. And we were really excited."]

[Jones - "It comes across. It comes across through the whole thing."]

MP3 Audio Clip (10 min 21 sec)

104:31:16 Young: I better go easy on this Landing Radar circuit breaker, huh?

104:31:19 Duke: Yeah, don't...Okay, that's the right one. Okay; (movie) camera's off. Ha, ha! Hey, it sure ain't flat, John. Wow! There's that ridge to the north.

104:31:33 Young: Yep. Sure is.

104:31:35 Duke: All we got to do is jump out the hatch and we got plenty of rocks.

104:31:38 Young: Houston, boy, it sure looks like you could make - I see Crown Crater (near the summit of Stone Mountain) from here; I can see (South) Ray Crater from here. Not a...Boy!

104:31:49 Duke: I almost had apoplexy, that Program alarm, and that's your radar breaker.

[Jones - "Was there a program alarm on the way down?"]

[Duke - "Oh; no. That was when he pulled the radar breaker (at 104:31:16). It gives you a program alarm."]

104:31:54 Young: Charlie's about had...(Laughs and changes the subject) Charlie's got nothing but a ridge to look at.
[John's comment suggests that Charlie was startled by the Program alarm.]
104:31:59 Irwin: Sounds beautiful, John. Wish I were there.

104:32:02 Duke: There's a ridge out in front (stops to listen to Irwin) There's a ridge out in front of us, too, John.

104:32:07 Young: Yeah. There's a ridge in front of us, one to the side of us, and my guess is that we're in a subdued old crater that's got a lot more craters (in it).

104:32:16 Irwin: Roger. We copy.

104:32:18 Young: What a neat place.

104:32:21 Duke: Okay, Jim, this ridge in front of us does look like a subdued crater and it may be the raised rim about 50 meters in front of us, about, oh, 4 or 5 meters tall. About 30 or 40 percent of the surface is covered with boulders that are maybe half a meter in size. On out in front of us and to the right, where we landed, there were...

[Duke - "If you look at the pictures we took, I was way off on my estimate. We were high. We were way high on those estimates about boulder size and about the percentage of covering over the surface. You know, we were so excited, it just looked like rocks everywhere. And there were a lot of rocks; but they weren't that big. And it's very difficult judging the size of objects that you've never seen before. 'Cause you really had nothing to compare 'em to, Eric. And, so, I just made a real bad error of judgment on the percentage of coverage of the rocks and, also, on the size of 'em."]

[We then looked at photos AS16-113- 18296 to 18310, which show the view out the LM window.]

[Frame 18296 shows Stone Mountain, which they will climb during EVA-2.]

[Frame 18297 shows the white ejecta blanket surrounding South Ray Crater.]

[Frames 18307 and 18308 are representative of the view out Charlie's window.]

[Duke - "See, it doesn't...Hardly any rocks to speak of, now that I look at it. But I was referring to these, like the one right there."]

[Jones - "On John's side, in 18300."]

[Duke - "On John's side. And here's one here. And there's one on out here. And these out here next to that crater, which was a little secondary, I think."]

[Jones - "Out your side, just above and to the left of the thruster in 18307."]

[Duke - "And I estimated it....See, this ridge is actually close in. And I estimated that ridge in here (forming the local horizon in AS16-113-18307 and 18308 as four to five meters high but I don't think it was. And you can see my estimates of the rock sizes are way off."]

[We then looked at a pan Charlie took early in EVA-1 from a spot about 20 meters northeast of the LM. These are frames AS16-113- 18313 to 18330.]

[Frames 18323, 18324, and 18325 show the 15-m crater that John overflew during the landing.]

[Frame 18328 shows John on the Rover, behind the LM, about to make his first test drive. John and the Rover are not easy to spot.]

[Duke - "This ( 18325 ) is looking off to the south."]

[Jones - "And there is a smidge of rocks but not a large number."]

[Duke - "This crater, we didn't really realize it had been there."]

[Jones - "You're just on the west edge of it."]

[Duke - "And I had to get the ALSEP (out of the SEQ Bay on the southeast face of the Descent Stage). The experiments were back here in the back and, if we had been a little bit closer (to the crater), I wouldn't have been able to do that. I'd have rolled down the hill there, into that crater. So, you can see, it looks like it's steep on this (east) side ( in AS16-113- 18323 ), but it actually comes up in here (on the west side in 18325), too."]

[In the following, John tells Charlie to hold off on the description of the landing site until they have word from Houston that the LM is in good shape.]

104:32:45 Young: Wait a minute, Charlie. (To Mission Control) We gonna stay, Houston?

104:32:48 Irwin: Stand by. (Long Pause) Everything's looking okay up to this point, John. We'll give you a final word here shortly.

104:33:14 Young: Okay. We were coming down pretty good until I hit the Stop button, and then it fell out. You know, the engine stopped.

104:33:22 Irwin: I know exactly what you mean. (Pause)

[Jim Irwin was the LMP on Apollo 15 and, on that flight, Dave Scott hit the engine-stop button quicker than any of the Commanders. Consequently, the Apollo 15 LM, Falcon, hit the ground at about 6.8 feet per second, about twice the speed that any of the other LMs touched down. It was a very hard bump. The relatively hard Apollo 15 landing was the reason John counted 'one-potato' between the time Charlie called the contact light and John hit the stop button.]
104:33:29 Young: It's really nice to have your shadow out there; that's a good help. It's a good altitude gouge (sic).
[Duke - "'Gouge' is a term synonymous really with 'gauge'."]

[Jones - "Hmm. I've never heard that usage before."]

[Duke - "At the Naval Academy, if you had the 'gouge', that means you had the answers to the test, that type of thing. 'Gouge' is synonymous to 'reference'. 'It's a good reference.' That's what it means."]

[Jones - "You started at the Naval Academy and then transferred?"]

[Duke - "Yeah; I started at the Naval Academy and then transferred to the Air Force."]

104:33:37 Duke: John, that was super. (Pause) AGS is updated. That's in. Batteries (are) all looking good, EPS (Electrical Power System) is looking good. Ascent quantities are looking...

104:33:58 Young: The way these blocks are laid in here, out my window, I'd guess they come from South Ray. There's some biggies out there. We've got, right out in front of us about 100 meters, at my 10:30 position (that is, southeast of the LM), I've got one that must be 3 meters across.

104:34:17 Irwin: Orion, you're stay for T-1.

104:34:22 Young: Understand.

104:34:23 Duke: Okay, stay for T-1. P68, John, and I'll get the AGS going. 414 plus 2 is in, 400 to 4.

104:34:40 Duke: Hey, Jim, hats off and a case of beer to FIDO (Flight Dynamics Officer). I'll tell you, that targeting was just beautiful.

104:34:46 Young: Boy! You guys just started us right in there. (Pause) That was superb!

104:35:53 Irwin: Very good. (Pause)

104:35:02 Young: (To Charlie) (Garbled) where it says we are. I believe it.

[Duke - "He's referring to the G&N (Guidance and Navigation) system."]
104:35:05 Duke: Okay, Jim, our Noun 43s are minus 896...

104:35:08 Irwin: We have them, Charlie.

104:35:10 Duke: ...plus 1552. (To John) Okay; (Reading) Engine Stop, Reset.

104:35:14 Young: Okay; Engine Stop, Reset.

104:35:16 Duke: Okay. Pro.

104:35:17 Young: Pro.

104:35:18 Duke: Call P12. (Pause)

104:35:24 Young: Go on in there, Charlie.

104:35:27 Duke: Okay. (Reading) Tig (time-of-ignition) time for T-2 is 104 (pause) plus 42 plus 16.64. Pro. (Long Pause)

104:35:52 Duke: Those numbers are good.

104:35:53 Young: Those numbers are good?

104:35:54 Duke: Yep.

104:35:55 Young: Outstanding. (Pause) Pro. It's Auto.

104:36:01 Duke: Auto.

104:36:03 Young: Pro. (Pause)

104:36:09 Duke: Okay; (Reading) "PGNS Mode Control, Noun 33", you got. 6 minutes, we're counting down.

104:36:16 Young: (To Houston) Boy, this is really a nice place! Feel that one-sixth g, Charlie.

104:36:20 Duke: My restraint harness has got me anchored.

104:36:24 Young: Oh, that's what the trouble is. (Pause)

[They are both wearing harness cables which are attached at the suit waist and to anchors on the floor. The harness cables keep them from moving around during the descent and launch. They will remove the harness cables once Houston gives them a stay for T-2.]
104:36:29 Duke: Okay, the AGS is set, 410. Standing by. (Pause) John, that was a sup(erb landing)! (Long Pause) It's just about level (that is, the LM is nearly vertical), we're not going to have a bit of trouble getting out...

104:36:57 Young: Yeah, it's going to be neat. But it sure is not...It's not a smooth...It's not that FS smooth, Houston.

104:37:08 Irwin: Say again, John.

104:37:12 Young: It's not that FS smooth; we're in the middle of a block field.

104:37:16 Irwin: Roger; we copy.

[As is discussed after 125:08:49 during the return to the LM at the end of the EVA-1 traverse, "FS smooth" is a joking reference to a smooth geologic unit on a map John and Charlie used during a field trip during training. Not having participated in the Apollo 16 geology training, Irwin doesn't understand the reference.]
104:37:17 Duke: (Looking out John's window to the south) There's Crown Crater up there (near the summit of Stone Mountain).

104:37:22 Young: (Garbled) little blocks. We may have squashed a few.

104:37:29 Duke: And, Jim, we got Crown Crater out John's left window (at) about 9 o'clock.

104:37:34 Irwin: Roger.

104:37:37 Young: And just looking at it from here, I don't think the Rover's going to have any trouble going up that hill.

104:37:41 Irwin: Glad to hear that.

104:37:45 Young: I could be wrong. Slopes tend to fool you. (Pause)

104:37:48 Duke: It looked good going (to) North Ray, too. There were some big blocks on the rim but not...The track just looked good.

104:37:54 Young: It looked good, huh?

104:37:55 Duke: Yeah. Uh-huh. (Long Pause)

104:38:24 Duke: (Garbled)

104:38:25 Young: Turn on the water for a second, Charlie.

104:38:27 Duke: Okay, that's a good idea. (Long Pause)

[There are two possible reasons for turning on the water. One is to get a drink from the water gun through a small port at the side of the helmet; and the other is to cool themselves down by running LM water through their Liquid-Cooled Garments (LCGs). The Apollo 15 crew did not wear their LCGs during the landing, but the Apollo 16 and 17 crews wore theirs because they planned to do EVAs immediately after landing.]

[Jones - "The squirt gun at the cheek? Did John want to get a drink of water?"]

[Duke - "Yeah, we're still helmeted at this time. Oh, no! It's not to drink. It's the cooling water for the LCG, 'cause we were getting warm."]

[Jones - "The suits are not pressurized at this time, I would presume. It would be impossible to fly the spacecraft, with the suits pressurized, wouldn't it?"]

[Duke - "Oh, no; you can fly it. Yeah, pressurized. Yeah, you could do that. We did that a couple of times, with no problem."]

[Jones - "It was more difficult?"]

[Duke - "Oh, yeah. Well, I mean, the gloves were bigger and all. Especially if you had manual control. But you could punch the switches and all. It was a little bit harder to hit circuit breakers and stuff with the gloves out and pressurized but, it was do-able."]

[Jones - "Let's see. You've got the IV (Intravehicular) gloves on, the ones without the thermal covering."]

[Duke - "That's right."]

[Jones - "So you would have had less bulk and a little more dexterity than with the EVA gloves?"]

[Duke - "Yeah. The IV gloves were sort of in between the (bare) hand and the EVA gloves. The EVA gloves were bulky and sometimes, to get a switch, your glove would barely fit in the switch guard. We just practiced and we didn't have any problem with it. You just had to be a little bit more careful."]

[Jones - "And you practiced to fly pressurized in case..."]

[Duke - "In case you land and a window pops out or you rupture the pressure vessel and you have to go back up (with suits) pressurized. So we had to practice that."]

104:38:50 Duke: That shadow is not as long as I thought it was going to be. It looks like we're right on top of the ground.

104:39:00 Young: Yeah, we didn't drop very far. (Long Pause)

[Jones - "Are you mis-judging the shadow length? Or is it really shorter because the ground's sloping up toward the west?"]

[Duke - "It is sloping up; plus we're late landing 3 revs, so the Sun angle's higher. My perception was that it would be a longer shadow and a farther horizon; but, with a sloping up terrain, it made it look like we were confined, in sort of a bowl. And that's what I meant by this."]

[The following discussion is taken from the Apollo Technical Debrief and begins with a discussion of visual effects in the down-Sun direction, also called "Zero-Phase". At zero phase, there is a considerable amount of sunlight reflected back to the observer due to a process called Coherent Backscatter and, consequently, the zero-phase direction tends to be very bright and washed out.]

[One interesting part of the following discussion is the fact that there was a shadow in the simulation.]

[Duke, from the 1972 Technical Debrief - "(To John) How about that Zero Phase? I never noticed it."]

[Young, from the 1972 Technical Debrief - "First, the thing (zero phase) starts out as a Sun (meaning a very bright patch of reflected light) coming and that turns to a (LM) shadow. That was zero phase getting better all the time."]

[Duke, from the 1972 Technical Debrief - "I was excited at that time."]

[Young, from the 1972 Technical Debrief - "Yes. When you said, 'here comes the shadow, that was before I had seen it (because the spacecraft was yawed left). In fact, you were watching it out your window and I looked up there and I saw it, and I said, 'Yeah, man; there's no doubt.' And that baby got bigger and bigger and dropped right down in front of us; and, man, that's a good gauge (of LM altitude)."]

[Duke, from the 1972 Technical Debrief - "Was it?"]

[Young, from the 1972 Technical Debrief - "Yes, we saw it in the (16-mm) film."]

[Duke, from the 1972 Technical Debrief - "It looked just like that one in the LMS (Lunar Module Simulator)."]

[In the following, John addresses himself to Deke Slayton, the former Mercury astronaut who was Director of Flight Crew Operations.]

[Young, from the 1972 Technical Debrief - "I don't know if you know this, Deke; they had a shadow for us (in the simulator window view), and I guess we've been using it. In fact, we'd been practicing (landing) without radar a couple of times just to see what you could do. The thrust-to-weight ratio in our lunar module is such that, if you're at 100 feet and you have 20 feet a second down, if you go full throttle, you'll have that (descent rate) all killed before you hit the ground. So (in training) we're looking at high sink rate descents off nominal with the shadow. Man, it really makes a difference when you're looking for it. A crater from 50,000 feet looks like a crater at 5 feet (meaning that is impossible to judge the absolute size of craters) - that's the bad part of it. But, with a shadow, as it gets bigger, you know you're getting close."]

104:39:15 Young: Man, we got a lot of rocks, that's for sure. (Pause)

104:39:22 Duke: (To Houston) How's it (meaning the LM) looking, Jim?

104:39:24 Irwin: It's still looking good. We're just standing by here...

104:39:27 Young: I wish I could tell you what kind of rocks those are Houston. But some of them are very white; and, doggone, if I could see...I'm not close enough to them, but...And I see one white one with some black...Can't tell whether that's dirt or not on it. But it could be a white breccia, if you believe such a thing.

104:39:51 Irwin: We copy.

[Jones - "There were certainly a number of people in the geologic community who were expecting that you would find basalts and other kinds of volcanic rocks, and not breccias."]

[Duke - "We had mostly trained volcanics. We did very little on the breccias and stuff like that. But we had seen the rocks from the earlier missions in the Lunar Receiving Lab. I guess we had expected it (breccias) somewhat. But most of our training and most of the pre-flight photo-geology had basically been two classes of volcanic rock. The Cayley Plain was one type of volcanic and the other would have been the highlands, the more viscous that created domes or hills. And I got the impression that the geologists were really surprised when we started describing all these breccias and crystalline rocks. And they were really...Either they thought we were dumb and, you know, really screwing up; or it was something they didn't really expect. In my mind, at first, I thought that when I started describing these things, these guys are going to think they wasted six years of geology on these two klutzes up there on the Moon. But then, I began to sense a general understanding (in Houston) that 'hey, things are different than we expected'. And then, they were beginning to get excited, too."]

[Jones - "The general impression that I have all through here - starting now, but particularly when you get outside - is that you guys were well prepared."]

[Duke - "Yeah, we were. We'd had - I guess it was - the equivalent of a master's degree in geology over the six years. John probably didn't get as much classroom-type geology as we (the fifth astronaut group) did. He was in the training cycle and he was going through late Gemini and early Apollo, so he didn't get the overall classroom geology training that our group got. But we made it a plan, right after we got picked for the (Apollo 16) crew...actually, for Apollo 13 when we were backup. We made it a practice to have one geology trip every month."]

[John and Charlie had eighteen geology field trips in the nineteen months from July 1970 to February 1972.]

[Jones - "Toward the end, I gather you'd go out and the geologists would be in a trailer somewhere."]

[Duke - "Yeah, and we'd have all the radios and we'd start describing. And towards the end, of course, we had the Rover mock-up that would work down here (the one-g trainer). And that was real good, to make it more realistic. And the geology trips we took were like to Hawaii; we went to Jackass Flats out there in Nevada where the nuclear test sites are; and we went to various other volcanically significant areas."]

[Dr. Fred Hörz, NASA geologist, from a 2003 e-mail - "The geology-training of astronauts started with general lectures and field trips (in large groups) shortly after their astronaut selections. Depending on these selection dates, astronauts may have had some 3-5 years of 'general' training, typically a 2-hour lecture per month, a 2-hour lab class (macroscopic rock descriptions) per month and some 2-3 field trips per year. This training was initially under the guidance of Gene Shoemaker and Dale Jackson of the USGS, but was taken over more and more by an ever growing staff of MSC (Manned Spacecraft Center) geoscientists."]

["In about 1969, a new geo-science management appeared at MSC under P. Gast's leadership, in anticipation of the returned samples; this new leadership team initiated a more rigorous approach, starting with Apollo 14: each crew (including back-up crew) selected for a mission was assigned a full time 'Mission Science Trainer' (A14: (Mike) McEwen; A15: (Gary) Lofgren, A16: yours truly, A17: D.Morrison) and we got two 2-hour sessions per week and a field trip of 2-3 days per month. The weekly sessions were typically one invited talk/lecture per week and one lab-class.]

["Ultimately all of the above 'trainers' participated in the training of all crews, but the above individuals were responsible for the overall training program of a specific mission and called the shots. Most field exercises were run in collaboration with the USGS, the official field geology team, yet the NASA-Science Trainers determined the content and substance of the overall crew-training and education, consistent with the specific mission objectives."]

["The field trips increasingly incoporated the entire surface operations, i.e. crew was in field with vehicle, lunar sampling tools,cameras, sample bags etc and some simulated backroom was somewhere out-of sight in a tent; communication of what the crew saw and collected/documented was exclusively via radio; the 'science trainer' was with the crew as a silent observer. A substantial debriefing followed each simulated EVA, the latter typically 4-6 hours long; most of the debriefing/critique occurred while everybody walked over the entire EVA together. Most of the lab-classes served to critique additional EVA matters, such as photodocumentation, samples bagged etc., after the crew trainer spent days of pouring over the materials collected and a few hundred 'surface photos' taken, etc."]

["Thus, the training was fairly rigorous and intensive. Note that the backroom in these exercises was composed of the same folks that also manned the science support room during the actual mission; we were familiar with each individual's nuances, lingo, observational skills etc. Granted, there were differences among individual crew members but all in all: they were excellent to thoroughly impressive - that is, very smart individuals and quick learners."]

["Unfortunately, none of this is documented in great detail; a number of attempts were made, but all were aborted for one reason or another."]

104:39:52 Duke: Every one of them are (sic) angular, too, John.

104:39:54 Young: Yeah, they're all angular. They're out of South Ray, I believe.

104:39:58 Duke: There's a pretty one over there, without any dust on it at all. Out about 50 meters, by those three little craters? (Pause)

104:40:07 Young: Right (Pause) In fact, Houston, when I told you that I thought this terrain might be very spectacular; boy, I was just kidding. It really is something looking at that mountain. That is a big mountain, Charlie!

[The summit of Stone Mountain is about 540 meters high and is about 5 kilometers south of the LM. In comparison, the tallest peak at the Apollo 15 site is 4500-m Mt. Hadley and, at the Apollo 17 site, the tallest peak is the 2500-m South Massif.]
104:40:30 Duke: Yeah, we're within 2 minutes (of T-2), John. Let's...(Pause) I agree with you. It is really (spectacular) (Pause) Is that South Ray? That big bright (garbled)?... (Long Pause)
[Charlie and I looked at AS16-113- 18300, a frame from a pan taken out John's window. There is a very bright patch just below the horizon on the right side of the picture.]

[Duke - "That's what we're probably referring to."]

[Jones - "Just above and to the right of the thrusters."]

[Duke - "That bright spot out there that we were thinking, maybe, was South Ray."]

[Jones - "That's some of the South Ray ejecta. You see it from lots of places."]

104:41:03 Irwin: Orion, you're stay for T-2.

104:41:08 Duke: Rog; ...

104:41:09 Young: Okay....

104:41:09 Duke: ...Super.

104:41:10 Young: ...Thank you.

104:41:14 Duke: Stay for T-2. Okay; let's go to P00, and then ICS PTT (Push-to-Talk). (Pause)

[They have initiated Program Zero-Zero - pronounced "Pooh" - so that Houston can update the on-board computer; and they have switched the comm system to Push-to-Talk and, now, will only be heard in Houston when they activate the microphones with either a switch on the handcontroller or a cable-mounted switch attached to the suit.]

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