[About 12 minutes prior to PDI, CapCom Ed Mitchell reads up a revised descent Pad that includes a 3.3 nautical mile south-to-north targeting correction. Mitchell tells Scott and Irwin that, as a result of the re-targeting, "You'll probably see some roll during PDI." At five minutes prior to PDI, Scott and Irwin power up the Landing Radar and, once Houston confirms that it is operating properly, the Flight Director takes a final poll of the Flight Controllers and then tells Mitchell to give Scott and Irwin a Go for PDI. Three minutes prior to PDI, Scott and Irwin yaw 50 degrees left for high-gain aim. Three minutes into the burn, they will yaw back to the face-up position for radar acquisition. And at four minutes they should get landing radar data. At about 7.5 minutes they will pass over the Apennine Front at an altitude of about 22,000 feet which is about 10,000 feet above the 12,000 ft ridge line. At about 9:24 they have pitchover at about 7000 feet. Mount Hadley Delta, which Dave will be able to see out his window, is 13,000 ft tall and can be seen on the left in AS15-87-11717 which was taken from the LM during the final pass over the landing site prior to the descent. A labeled version is also available. The highest peaks in Apennine Front to the east are about 15,000 feet high.]MP3 Audio Clip ( 19 min 19 sec )
104:26:11 Mitchell: And, Falcon, you are Go for PDI (Powered Descent Initiation).
104:26:19 Scott: Roger. Go for PDI. (Long Pause)
[Stephen Tellier has provided a pre-mission illustration of the planned LM ground track from PDI to landing ( 2.9 Mb or 640k ).]104:26:38 Irwin: (Garbled)
104:26:43 Scott: Okay. Endeavour, how do you read the Falcon?
104:26:45 Worden: Falcon, Endeavour. Reading you loud and clear there, Dave. (Long Pause)
104:27:08 Scott: Endeavour, Falcon. If you're reading, we're not reading you.
104:27:13 Worden: Falcon, Endeavour. How do you read? (Pause)
104:27:22 Mitchell: Falcon, Endeavour's reading you loud and clear.
104:27:27 Scott: Okay; fine. Thank you. (Long Pause)
104:27:40 Irwin: Stand by for 1 minute.
104:27:41 Scott: Okay. (Pause)
104:27:51 Irwin: (The readings) on our oxidizer...They're low, aren't they?
104:28:00 Scott: Yeah.
[In Houston, the knowledgeable Flight Controller tells the Flight Director that this condition is normal prior to the ullage burn described below. The readings will rise to normal values after the PDI burn starts.]104:28:02 Irwin: (Garbled) cycle the cir(cuit breaker).
[Journal Contributor Frank O'Brien notes, "Jim is probably referring to the Propellant Quantity Measurement Device (PQMD) circuit breaker. His suggestion to 'cycle the breaker' - which means turning power to the system off, and then back on - is intended to reset the PQMD, with the hope that a more 'normal' reading will result."]104:28:04 Scott: No. That's all right. Be accurate later on. (Pause)
104:28:14 Irwin: Houston, we're reading 87 and 85 on the Fuel Quantity (gauge).
104:28:19 Mitchell: Roger. Roger. It'll come up here in a moment. (Pause) It looks good to us, Jim.
104:28:35 Irwin: Okay. (Long Pause)
104:29:09 Mitchell: Mark. One minute. (Pause)
104:29:13 Scott: Okay. Master Arm's On; I have two (pyrotechnic system) lights. (Long Pause)
[With the Master Arm switch On, Dave will be able to fire the small explosive charges that open the valves connecting the helium pressurization system to the tanks holding the descent stage oxidizer and propellant.]104:29:39 Scott: Average G. Armed the Descent (engine). We have guidance.
104:29:47 Irwin: (Standing) by for ullage.
104:29:49 Scott: Standing by for ullage. (Long Pause)
[In normal usage, 'ullage' is the empty portion of a cask. Here, the word is used to denote a brief firing of the LM's steering jets against the LM's orbital motion. This brief firing of the Reaction Control System (RCS) will provide enough acceleration to separate the propellant in the tanks from the helium that provides tank pressure. The ullage burn settles the propellant to the bottom of the tank next to the exit ports so that the heavier propellant - and not the lighter helium - flows through the valve at engine ignition. The LM computer will perform the ullage burn, with Dave providing a manual backup.]104:30:03 LM Crew: Ullage.
104:30:05 Scott: Go for the Pro. Pro.
[Next, they will tell the computer to continue execution of the program that will fire the descent engine and control the descent down to an altitude of about 7000 feet (2.1 km). Other programs were then run to provide guidance from there to the surface.]104:30:08 Irwin: Pro-ing. (Pause)
104:30:12 Scott: Auto ignition. (Pause) Eleven percent (throttle); the (Descent Engine Command) Override is On. (Long Pause)
[O'Brien - "The Descent Engine Command Override, as the name implies, allows the crew to override the computer's commanded thrust level of the descent engine. The Thrust/Translational Handcontroller, which is at Dave's left hand, is used to adjust the engine thrust. For the first 26 seconds, the engine fires at about ten percent of maximum thrust so that the guidance system can gimbal the descent engine to point through the LM's center-of-gravity. This procedure must be completed before the engine is throttled up to maximum thrust."]104:30:37 Scott: Throttle up. (Pause)
104:30:43 Irwin: Okay. Master Arm, Off.
[O'Brien - "I'm still trying to determine why the Master Arm was always turned off after a few seconds into an engine burn. I know it has to do with computer-initiated engine shutdown, but it doesn't completely make sense. Pete Conrad forgot to turn it off during the Apollo 12 ascent, and had to shut down the engine manually, resulting in a ~1.5 second overburn."]104:30:44 Scott: Okay. Master Arm is coming Off. Lights are Off. Looks stable.
104:30:52 Irwin: H-dot's looking a little higher than normal.
104:30:56 Scott: Okay. We're a little higher than normal. (Pause)
[They have begun the burn at a slightly higher than planned altitude and, to compensate, the computer is giving them a descent rate slightly greater than planned. H is altitude and H-dot is the rate-of-change of altitude (descent rate), that is, the time derivative. Jim is consulting a table in the LM Timeline Book which shows the planned altitude and descent rate at various times during the burn and is comparing those figures with the computer displays of the Primary Guidance and Navigation System (PGNS) computer and the Abort Guidance System (AGS) computer. Dave operates the PGNS (pronounced "pings") and Jim the AGS (pronounced "ags").]104:31:11 Irwin: One minute (into the burn). H-dot's about 20 (feet per second) high.
104:31:16 Scott: Okay.
104:31:18 Irwin: Fuel is a little low; oxidizer is a little high. (Pause)
104:31:25 Mitchell: Falcon, Houston. A (Noun) 169: minus 02800.
[This is a guidance update - based on Earth based tracking - to correct for about a 2800 foot undershoot of the planned landing site.]104:31:37 Scott: Roger, minus 02800. Standing by for the Enter.
[Journal Contributor Paul Fjeld notes that the ability to update the LM targeting "was added on Apollo 12. DLAND - Noun 69 - was a dangerous vector! It was added to the Position of the landing site (RLS) every 2-second cycle, then zeroed. The crew had to verify that the three registers were all balls (all zero), then only put the Delta-Z value (downrange change in position) in R1, then only press enter when MCC looked at the DSKY downlist to verify that the number was good. Noun 69 was one of the easiest opportunities for the crew to kill themselves."]104:31:43 Mitchell: You're Go for Enter.
104:31:46 Scott: Go for Enter. (Long Pause)
[Houston can watch them do the keyboard entry of the update and is confirming that they have entered the correct data. By punching the Enter button, Dave and Jim are telling the PGNS to incorporate the keyboard entry into memory. While Dave types the entry, Jim watches him do it and, in effect, they have a triple check of all entries into the computer.]104:32:07 Mitchell: Falcon, Houston. You're Go at 2 minutes.
[In Houston, the Flight Director polls the Flight Controllers and confirms that LM performance is as expected.]
104:32:13 Scott: Roger, Go at 2. PGNS and AGS compare.
[The PGNS and AGS use independent sensing systems to determine the trajectory and the fact that they agree is reassuring to all concerned.]104:32:18 Irwin: H-dot's a little high. We're about 2 percent low on fuel.
104:32:23 Scott: Okay.
104:32:24 Irwin: At one (minute). (Long Pause)
[In Houston, Ed Mitchell requests permission to tell the crew that the Flight Controllers believe that the fuel quantities are actually normal.]104:32:41 Mitchell: Fal...
104:32:42 Irwin: 3 (garbled) good...
104:32:43 Mitchell: Falcon, Houston. We're...
104:32:44 Irwin: H-dot's 4 (feet per second) high.
104:32:47 Mitchell: Falcon, Houston. We're happy with your fuel.
104:32:53 Scott: (Light-heartedly) Okay; that's nice to hear. (Long Pause)
104:33:09 Scott: Okay; 3 minutes, it's yawing to zero.
[The computer is rotating the spacecraft around the thrust axis into a windows-up orientation. Dave and Jim are now flying with their backs to the Moon and their feet pointed along the orbit.]104:33:13 Irwin: Altitude is good. H-dot's right on, Dave.
104:33:16 Scott: Good.
104:33:17 Irwin: Still reading two percent low. Glad Houston's happy with it.
104:33:21 Mitchell: Falcon, Houston. You're Go at 3.
104:33:25 Scott: Roger, Go at 3. Altitude light is out. We have a 3400 Delta-H. (Pause) Velocity light is out. Delta-H looks good up here, Houston. What do you think?
[The fact that the altitude and velocity lights have gone out indicates that the computer is now getting what it considers to be acceptable data from the landing radar. Delta-H is the difference between the altitude given by the radar, and the altitude above the terrain computed by the PGNS.]104:33:45 Mitchell: Falcon, Houston. We agree with Delta-H. Accept.
[O'Brien - "Because the computer uses only a simplistic, five segment model of the mountainous terrain below, Delta-H is the difference between the altitude above the mountains as determined by the landing radar, and the calculated elevation of the surface in the model. If the terrain model were perfectly accurate, and if Falcon were flying a perfectly accurate approach path (rather than being somewhat south of the desired track), Delta-H would be zero. A model of the approach-path terrain was first incorporated in the guidance routines for Apollo 14."]
104:33:52 Scott: Roger. Accept. It's going in.
[They are telling the computer to start using the radar data.]104:33:58 Irwin: And, Houston, ED batteries check.
104:34:01 Mitchell: Copy. (Pause)
[Jim has just checked the voltage on the batteries which would fire the small pyrotechnic charges - called Explosive Devices (EDs) - that would separate the LM stages in the event of an abort using the ascent engine for a return to lunar orbit.]104:34:12 Irwin: 4 minutes. Altitude is 2000 high.
[David Woods has provided scans of pages 15 ( 1.0Mb ) and 16 ( 1.0Mb ) from the Apollo 15 Lunar Module Cue Cards, which cover various abort scenarios. On page 16, for a return to orbit using either the descent engine (lefthand column) or the ascent engine (righthand collumn), Dave would check the position of the Guiance Switch and then push either the Abort button or Abort Stage button, respectively.]
104:34:15 Scott: Okay.
104:34:16 Irwin: About 3 low. Fuel and Oxidizer looking good (within) 1 percent (of the planned values).
104:34:21 Scott: Okay. PGNS and AGS look good. (Long Pause)
[Figure 7-3 in the Apollo 15 Mission Report shows the altitude readouts of the PGNS and AGS. Note that the horizontal axis is mislabeled. The label 104:30:00 is correct but the next one to the right should read 104:34:00 instead of 104:30:34, and so on. After the crew told the PGNS to accept landing radar updates, the computed altitude leveled off at about 42,000 feet for approximately one minute and then stayed above the AGS altitude for another three minutes. According to the Apollo 15 Mission Report, the difference was due, primarily, to an improper value used by the computer for the slope of the mare surface near the landing site. As the LM approached the landing site, the effect of the slope on the altitude calculation became less and less important. The AGS does not use the radar data and, so, was unaffected.]104:34:42 Irwin: 4:30. Altitude's 4000 high, H-dot's right on. Fuel and Oxidizer good.
104:34:48 Scott: Okay. Delta-H is 2000. (Long Pause)
[In Houston, there is an on-going discussion about the validity of the Fuel Quantity gauge Number 1 reading.]104:35:11 Irwin: 5 minutes. Altitude, 4000 high. H-dot, about 9 (feet per second) high.
104:35:18 Scott: Okay.
104:35:19 Mitchell: Falcon, Houston. You're Go at 5, and your fuel quantity looks good here. (Pause)
104:35:25 Scott: Okay; understand. Go at 5. (Long Pause)
104:35:42 Irwin: Altitude is 3000 high. H-dot, 10 high. Fuel and oxidizer, good.
104:35:50 Scott: Okay. (Long Pause)
104:36:13 Irwin: Altitude, 2000 high. H-dot, 6 high.
104:36:16 Scott: Okay. It's coming in.
[That is, the altitude error is steadily decreasing as they descend to the planned trajectory.]104:36:17 Irwin: Oxidizer, good.
104:36:19 Scott: And the Delta-H is looking pretty good.
104:36:26 Mitchell: Falcon, Houston. You're GO at 6 (minutes).
104:36:31 Scott: Roger. Go at 6. 30 K (30,000 feet altitude).
104:36:43 Irwin: Altitude, a thousand high. H-dot, about 4 high.
104:36:47 Scott: Okay, x-axis override's out.
104:36:50 Mitchell: Falcon, Houston. Throttle down 7 plus 23.
104:37:03 Scott: Roger. 7 plus 23. (Pause)
104:37:12 Irwin: Seven minutes. (Garbled) thousand high. H-dot just about on. Oxidizer's running just about 1 percent low. (Long Pause)
104:37:33 Irwin: Throttle down (to 57 percent of full thrust).
104:37:34 Scott: Throttle down. 7 plus 22. (Pause)
104:37:43 Irwin: (Garbled) 30. (Garbled).
104:37:46 Scott: Okay.
104:37:47 Irwin: Oxidizer, good.
104:37:48 Scott: Okay. (I'll) check the manual. (Pause)
[Scott, from the 1971 Technical Debrief - "I evaluated manual control with the PGNS Mode Control switch in Attitude Hold. All I did was check roll, pitch, and yaw to see if we had any red flags and (then) went back to Auto. Everything seemed to be in order."]104:37:55 Scott: No flags. Looks good. (Pause)
104:38:08 Mitchell: Falcon, Houston. Descent 1 (fuel gauge).
[They have two fuel gauges and Houston believes that the number 1 gauge gives the more conservative reading.]104:38:14 Scott: Roger. Descent 1, and looks like P64 at 9:23.
104:38:19 Mitchell: Roger. (Long Pause)
[P64 is the program which will control the descent through pitchover, when the spacecraft tilts forward to a more upright orientation and they get their first view of the landing site.]104:38:38 Irwin: Good at eight (minutes) Mark. Good. (Long Pause)
[Scott, from the 1971 Technical Debrief - "I called up a Noun 68 to check the time at which P64 would occur, and it was 9:23, which was nominal"]
[In Houston, the Flight Director is told that tracking data indicates that the LM is headed for a point about 3000 feet south of the planned target. At first, the Flight Director decides not to tell the crew, knowing that Dave will see the difference at pitchover. However, Ed Mitchell immediately suggests that Dave be told. Mitchell flew as LMP on Apollo 14 and knows the value of having as much pertinent information as possible. The Flight Director approves Mitchell's request without hesitation.]104:39:17 Mitchell: Falcon, Houston. We expect you may be a little south of the site, maybe...
104:39:18 Irwin: Okay. Coming up on 8000 (feet altitude).
104:39:19 Mitchell:...3000 feet.
104:39:24 Scott: (Responding to Mitchell) Okay.
[Scott, from the 1971 Technical Debrief - "Just prior to P64, two events occurred which biased my estimation of where we were going to land. The ground called us and told us we were going to be 3000 feet south. Right?"]Mpeg Clip (time lapse; 3.0 Mb)
[Worden, from the 1971 Technical Debrief - "Yes, I recall (hearing) that from the Command Module".]
[Scott, from the 1971 Technical Debrief - "(The second event was that) I looked out the window, and I could see (Mt.) Hadley Delta. We seemed to be floating across Hadley Delta and my impression at the time was that we were way long because I could see the mountain out the window and we were still probably 10,000 to 11,000 feet high. I couldn't see the rille out the forward corner of the window, which you could on the simulator, out the left forward corner. So, I had the feeling from the two calls that we were going to land long and south."]
[Scott, from the Apollo 15 Mission Report - "At an altitude of approximately 9000 feet, the upper fourth of Hadley Delta Mountain was visible out of the left window."]
[The summit of Hadley Delta is about 11,000 feet above the valley floor. The mountain is on the left side of AS15-87-11717 with St. George Crater prominent on its northwestern Flank where Hadley Rille winds around the base. The picture was taken from the LM on the final pass over the landing site prior to the descent.]
[Scott - "The feeling of slow, forward, floating motion was experienced and, because of the relative position and motion with respect to the mountain, an impression of a downrange overshoot was experienced."]
[The following is taken from the partial Apollo 15 mission review I conducted with Jim in 1989 at his office in Colorado Springs.]
[Irwin - "(Chuckling) We're not looking down as we come over the mountains. We're looking (more or less) straight up until we get down to around 6000 feet and we pitch forward about 30 degrees and, at that point, we could look forward and see where we were. We could see the mountains. I was startled because, out the (left) window, I could see Mt. Hadley Delta which towered about six or seven thousand feet above us. And we never had that type of presentation in the simulator. We just had the front view, not the side view. When we pitched over, I could see the mountain that towered above us out Dave's window. I'm sure it startled Dave, too, because we wanted to know, you know, were we coming in to the right place? Fortunately, the rille was there and it was such a beautiful landmark that we knew we were coming in to the right area. But we'd never had that side view in any of our simulations. It was just the front view. A level plain with the canyon. And it would have been very impressive to be able to look out as we were skimming over the mountains with about 6000-foot terrain clearance. At that speed it would have been really spectacular, like a low-level pass as we came over the mountains down into the valley."]
[Jones - "What was the nature of the simulation that you looked at in training? It would have been early for a computer sim."]
[Irwin - "Well, the simulation was actually a model of the surface that the (U.S.) Geologic Survey had done. And then we had a television camera that would move over the surface as we came in and that was then portrayed to us in the Lunar Module."]
[Jones - "How big was the model that the camera flew to?"]
[Scott - "About 15 feet by 15 feet. And we very seldom looked at the whole thing. We look at the landing site part."]
[Jones - "And you rarely went into the place were it really was. It was ceiling mounted, was it not?"]
[Scott - "I think so. I remember having looked at it, but I didn't spend much time. I looked at it a lot out the (LM simulator) window. And when you look at it out the window, you don't see the edges (laughing)."]
[Journal Contributor Frank O'Brien has provided a view of the LM Mission Simulator (right) and the Landing and Ascent Facility (left) and, also, a view of the CSM Mission Simulator.]
RealVideo Clip by Ken Glover from the NASA film Apollo 15: In the Mountains of the Moon (not realtime)
104:39:32 Irwin: 7000 feet. P64!
104:39:36 Scott: Okay.
104:39:37 Irwin: We have LPD.
[LPD is the Landing Point Designator. In this mode, Dave can use his handcontroller to tell the computer to alter its target left or right, forward of back. From the computer readout, Jim will give Dave an angle which tells him where to look through scribe marks on the window to find the place where the computer thinks they will land. There are matching scribe marks both on the inner and outer panes of Dave's window and, if he positions himself so that those two sets line up, he will be looking at the proper point on the surface.]104:39:40 Scott: LPD. (Pause) Coming right.
[O'Brien - "Now that the landing area is in sight, Dave is making the first of 18 redesignations of the landing site, correcting the approach path to the right moved the targeted landing site to the north."]104:39:45 Irwin: Four-zero (LPD angle)
104:39:47 Irwin: 5000 feet. (LPD angles) 39. 39. 38. 39.
104:39:56 Irwin: 4000 feet. 40. 41. 45. 47. 52.
Mpeg Clip with Audio (2 min 37 sec; 20.3 Mb)
QuickTime version compressed by Peter Dayton from the Teague digitization (2 min 37 sec; 1.8 Mb)
104:40:06 Irwin: 3000 feet. 52. 52. 51. 50. 47. 47.
104:40:21 Irwin: 2000 feet. 42.
104:40:26 Scott: Okay. I got a good spot.
104:40:28 Irwin: Good. 42. 43.
[Scott, from the 1971 Technical Debrief - "When we pitched over, we got P64 right on time. As we pitched over and I looked out, there were very few shadows as far as craters go. I think the (USGS site) model gave us the impression that we could see many craters on the surface because of the shadow lines (that is, that they would see shadows in many craters). I believe the overall problem was the enhancement of the photography that was a little too high-fidelity. In other words, I think they over-enhanced the photography and made themselves think the terrain had more topographic relief than it really did."]104:40:31 Irwin: 1800 feet.
[The model was derived from relatively low-resolution Lunar Orbiter photographs - showing objects only larger than 20 meters. In their interpretation of those photographs, the USGS analysts over-estimated the depth-to-diameter ratios of the craters, particularly the smaller ones, and, therefore, overestimated the number of shadowed craters the crew would see under lighting conditions they would have during the descent. Compare a pre-mission map showing many, well-defined craters with a photo taken from the LM on the final pass over the landing site prior to the descent. When the latter photo was taken, the shadows were more prominent than they were during the descent.]
[In a 1995 letter, Dave pointed out that most of the craters around the Hadley target are shallow - with small depth-to-diameter ratios - and, if the L&A model was based on photographs taken at a lower Sun angle than the one he and Jim had during the actual landing, the photos - and, hence, the model - would have shown more craters than they actually saw.]
[Scott, from the 1971 Technical Debrief - "When we pitched over, I couldn't convince myself that I saw Index Crater anywhere. I saw, as I remember, a couple of shadowed craters, but not nearly as many as we were accustomed to seeing (in the LM simulator). I measured my east-west (uprange-downrange) displacement by my relative position to the rille, and I could see we were in fairly good shape, relative to the rille, but we were south. I could see the secondaries (probably the craters of the South Complex). I could see some shadowing in the areas in which the secondaries occurred. Knowing that we were 3000 feet south, which I am sure will be discussed in the debriefing...Because that's not what they meant. I don't know whether you know that or not. They didn't mean 3000 feet south, apparently. They meant azimuth. They meant that we were not coming in on 91 degrees (that is, from a direction one degree south of east). We were coming in at some other azimuth. But my interpretation was that our landing point had been moved. I'm sure that we'll get that in the debriefing, but that was a confusing call. We were south, and I redesignated immediately (with the LPD) four clicks to the right (north) and then, very shortly thereafter, after you called me again on the LPD numbers, I redesignated two more right and three uprange."]
["I saw what I thought was Salyut Crater and the smaller crater to the north of Salyut, both of which are quite subdued on the (Landing and Ascent or L&A) model. I think, in fact, what I was seeing was Last Crater. The Last Crater on the model is rather a sharp-rim crater with shadows, and Salyut and the one north of Salyut are rather subdued. I think what I selected was a landing site relative to Last Crater rather than Salyut Crater, but it looked like Salyut and the one north of Salyut to me, and that's where I redesignated to. I'm not sure how many other redesignations I put in heading for the target as Jim called the numbers. I may have put in a couple more."]
["I got busy, at that time, attempting to select a point for the actual landing. I guess our pre-flight philosophy had been that, if we were on target, we would try to land exactly on target. If we had a dispersion, we would select some point within the 1-kilometer circle which looked like a good place to land and (then) would land as soon as possible so as not to get behind in the propellant curve. Once I realized that we were not heading for the exact landing site, and that I didn't have a good location relative to Index Crater, I picked what I thought was a reasonably smooth area and headed directly for that."]
[According to the Apollo 15 Mission Report, Dave made a total of 18 redesignations which, collectively, moved the target 338 meters (1110 feet) uprange and 409 meters (1341 feet) north.]
[Scott - "One of the problems we had on the descent - and we talked about it briefly yesterday - once we pitched over and looked out, we had four craters that we lined up on the model and the maps for our landing chute: Matthew, Mark, Luke, and Index. Now, we couldn't use 'John' because of Madalyn (Murray) O'Hair. That's the truth. And, boy, those were great craters and they were lined up and we spent hours training on those craters. We called the last one Index, because Index was where we were supposed to land. And I'm sure that - because the available Lunar Orbiter photos had such poor resolution - they enhanced our maps and photos with features that probably either were different or were not there. And the problem was, when we pitched over and looked out the window, there was nothing there! I mean, Matthew, Mark, Luke and Index were there, but very subtle."]
[Madalyn Murray O'Hair was a well-publicized, militant atheist of the time who, among other things, sued NASA after the Apollo 8 crew read from Genesis during a Christmas Eve broadcast from lunar orbit in 1968. That suit was eventually dismissed by the U.S. Supreme Court.]
[Relevant maps are Pan camera frame 9430 (scan by John Pfannerstill), the post-mission map showing the traverses, and a site map showing feature names.]
[Readers interested in a deeper insight into the remainder of the landing sequence and the ways in which Dave and Jim worked together as a superbly-coordinated team may wish to read Dave Scott's post-landing commentary before continuing.]
104:40:32 Mitchell: Falcon, Houston. You're Go for landing.
104:40:33 Irwin: 44. 45.
104:40:36 Scott: Rog. Go for landing.
104:40:39 Irwin: 44. 45.
104:40:43 Irwin: 1000 feet. 45.
104:40:47 Irwin: 900. 45.
104:40:49 Irwin: 800. 45.
104:40:53 Irwin: 700. 46.
104:40:58 Irwin: 600. 48.
104:41:02 Irwin: 500. 49. Minus 17 (feet per second descent rate). Minus 15.
104:41:08 Irwin: 400 at minus 14. You've got P66.
104:41:13 Scott: Okay.
[Jim is confirming that Dave now has manual control of the spacecraft.]104:41:15 Irwin: 300 feet. Minus 11. (Pause) Minus 11.
[O'Brien - "Using the ROD (Rate-of-Descent) switch at any time during the approach phase would switch the computer from the currently running program, P64, to P66, the landing phase program. This switch, located near the attitude controller, was Dave's primary means of controlling vertical velocity. Changing the thrust of the descent engine using the Thrust/Translational Handcontroller was not practical, since small adjustments to the rate of descent was not easily done."]
["Because Dave disengaged the Landing Point Designator function when he assumed manual control, he no longer wants angles but, rather, his rate of descent. Below an altitude of 500 feet, they are flying in what Dave described in a 1995 letter as the 'zone of unforgiveness'."]
[Scott, from the 1971 Technical Debrief - "We got down to 400 feet, and we had planned to switch to P66. I gave one ROD click at that time. Jim called me on the P66, which verified the ROD was working, and I went down to 200 feet and started rounding out (that is, slowing the descent), at 150 feet."]
104:41:22 Irwin: 250. Minus 11; 9 percent fuel (remaining).
104:41:28 Irwin: You're 200. Minus 11.
104:41:31 Irwin: 150. Minus 7. Minus 6.
104:41:36 Irwin: 120 feet. Minus 6.
104:41:39 Scott: Okay. I've got some dust.
[Scott, from the 1971 Technical Debrief - "I could see dust - just a slight bit of dust. At about 50 to 60 feet, the total view outside was obscured by dust. It was completely IFR (Instrument Flight Rules). I came into the cockpit (that is, switched his attention from the view out the window to the instrument readings that Jim was giving him) and flew with the instruments from there on down."]104:41:40 Irwin: Minus 5; 100 feet at 5; nine percent fuel; minus 5.
104:41:46 Irwin: 80 at 5. Minus 3.
104:41:51 Irwin: 60 at 3.
104:41:54 Irwin: 50 at 3. Cross-pointers look good.
[Scott - "I got the altitude rate and altitude from Jim, and rounded out to 15 feet (altitude) and 1 foot per second (descent rate) for the last portion."]104:41:58 Irwin: 40 at 3.
[Jones - "Could you explain cross-pointers?"]
[Scott - "They are your horizontal velocity and lateral velocity on the attitude gyro (or Cross-pointer Indicator). Two needles like an ILS (Instrument Landing System, a precision aircraft landing aid). It gives your rate laterally (left and right) and forward and aft in feet per second, and you want them to be zero when you land so you don't have any forward or lateral velocity. It was a system I liked, even though I wasn't actually looking at the cross-pointers. I was still outside. We had trained enough that Jim would call anything to me that didn't look exactly right. And he would call the things that I wanted that looked right. So what he was telling me is something I would have normally looked at, at the last moment, to check myself. In the dust, I can't see whether we're going this way or that way. I could have looked at them. But I didn't have to look at them because he did it for me, 'cause he knew I wanted to look at them, and I knew he knew what he was looking at."]
[Journal Contributor David Harland notes a discrepancy between Dave's statement to me that he was 'outside' and his statement in the Technical Debrief, reproduced at 104:41:39, that he 'came inside'. In response to the question, Dave provided the following in a 15 March 1998 message.]
[Scott - "Each of the two comments was directed to a different 'audience' -- and they are therefore relative in weighting. That is, it was actually a function of my cross check. For the most part, I stayed outside with my eyes because Jim was providing almost all of the information I needed. However, the one parameter he did not provide was attitude, i.e., the LM roll, pitch and yaw relative to the local vertical. The LM does this automatically in the attitude-hold mode. However, just to make sure, I would occasionally take a quick glance (about 0.1 sec) at the 8-ball to verify that we were in a level attitude -- this is the cross-check part. I could have used, or scanned, the remainder of the instruments, but those were the ones from which Jim was passing the information verbally. Therefore, from 60 feet on down, I was essentially 'on the gauges', but unlike a fighter where they are all visual, the 'gauges' were the 8-ball and Jim's voice -- which enabled me to spend most of my time out of the window searching in the dust for the surface. Therefore, perhaps we could say that in the Tech Debrief I was in the cockpit with eyes AND ears; which allowed me to keep my eyes mostly outside and thus I essentially did not bring my eyes back in -- but spent probably 95% of the time outside. And the time from 60 ft to touchdown was only seconds anyway."]
[We now return to the Mission Review.]
[Jones - "In the Tech Debrief, you said you lost the surface at about 60 feet. John (Young, Apollo 16) and Pete (Conrad, Apollo 12) talk about being able to see a few rocks through the dust to give them a little judgment on left/right, forward/back. There weren't very many rocks around your site."]
[Scott - "There weren't many rocks around, and I don't remember seeing anything. It was just a white-out. I remember totally listening to Jim. I didn't bring my eyes back in, I stayed out there 'cause I was looking for something. I didn't have to bring my eyes back in, because my second pair of eyes were doing the job."]
104:42:02 Irwin: 30; 3.
104:42:05 Irwin: 25; 2; seven percent fuel.
104:42:12 Irwin: 20 at 1.
104:42:14 Irwin: 15 at 1. Minus 1, minus 1; six percent fuel.
104:42:22 Irwin: 10 feet. Minus 1.
104:42:27 Irwin: 8 feet. Minus 1.
104:42:29 Irwin: Contact. (Pause) Bam!
[Irwin - "We did hit harder than any of the other flights! And I was startled, obviously, when I said, 'Bam!' (Laughing) And I think Dave didn't particularly appreciate my comment, that he made a hard landing on the Moon!"]104:42:36 Scott: Okay, Houston. The Falcon is on the Plain at Hadley.
[I have been able to find estimates of the vertical speed at touchdown on five of the six landings. Neil Armstrong's was the lowest at 1.7 feet/second because he didn't get the engine shutdown until after the footpads were on the surface. On Apollo 12, 14, and 17, the landing speeds were all between 3.0 and 3.5 feet/second. Dave's was by far the highest at 6.8 fps, most likely because he was the fastest to hit the engine stop button and, therefore, fell the farthest. See the extended discussion below.]
['The Plain' is a reference to Dave's alma mater, West Point. See his comment after 104:49:52.]104:42:40 Mitchell: (With background applause in Houston) Roger, Roger, Falcon.
104:42:48 Irwin: No denying that. We had contact (that is, it was a hard bump). (Long Pause)
[Scott, from the 1971 Technical Debrief - "There was a rumble when we landed. I think all the equipment on board rattled. It seemed as if I could hear it all (despite the helmet he was wearing) when we landed, like you would shake the vehicle. Couldn't you hear that?"]104:43:08 Irwin: Okay. ECS (Environmental Control System, which keeps the cabin pressurized, etc.) looks good. (Pause)
[Irwin, from the 1971 Technical Debrief - "Yes, I agree."]
[Jones - "When Jim said 'You've got P66', is it fair to assume that you were looking out the window?"]
[Scott - "As I recall, I went out the window as soon as we got down there (that is, at pitchover). Everything inside is for Jim. For me to come in and go back out, really takes too much time. You know, I might comment on this part of it. Another objective we had, based on the previous flights, was to stay on a constant flight path - a constant rate of descent - and get it down. The previous flights, as I recall, had all leveled out high and then had come back down. And we looked at their trajectories, and it seemed to be a trend, that the guys would start stopping too soon and use up a lot of propellant, doing a stairstep thing. So one of the things that we trained on and thought about, was to keep it going and keep it coming down a constant flight path so that we could save gas for the hover, if we needed it. The stairstep appeared to be a trend that people got into because there's no definition on the ground. There's no runway. With the LLTV (Lunar Landing Training Vehicle), you have the runway and it's very easy to determine how high you are when you know how wide the runway is and how long it is. When you get to the Moon, there's no runway. There's nothing there to tell you how high you are; and I think the trend had been for people to start slowing up their rate of descent too soon - because, of course, you don't want to get too close, too fast, 'cause then you can't stop."]
[The LLTV - sometimes called The Flying Bedstead - was an open framework vehicle which, according to Journal contributor Ed Hengeveld, was equipped with a "General Electric CF-700-2V turbofan engine which provided 18,850 Newtons of thrust and could be throttled to support five-sixths of the 1815 kg weight of the vehicle. Lift for the remaining one-sixth of the LLTV's weight was provided by two 2250 Newton hydrogen peroxide lift rockets. These engines were operated by the pilot to simulate the engine that the Lunar Module would use during its descent to the Moon." The LLTV was also equipped with a set of maneuvering thrusters similar to those on the LM so that the pilot could get a seat-of-the-pants feel for flying the LM. Only the Commanders and backup Commanders flew the LLTV. In training for Apollo 15, Dave made 32 LLTV flights between February 16, 1970 and July 1, 1971. He had, of course, previously flown the LLTV as the Apollo 12 backup Commander and also spent time in a LLTV simulator. See, also, Gene Cernan's discussion of the LLTV at 113:43:49 in the Apollo 17 Journal.]
[Scott, from the 1971 Technical Debrief - "The LPD was real good. I felt we were heading toward the point for which the numbers were being read. Manual control on the vehicle was excellent. I think it was more positive than the LLTV. I'll make one general comment. I felt very comfortable flying the vehicle manually, because of the LLTV training, and there was no question in my mind that I could put it down where I wanted to. We landed exactly where I was headed. In spite of the fact that the rear pad was in a crater, that's just where I wanted to land. I think our horizontal velocities were zero lateral and I had about 1 foot per second forward to keep from backing into anything. That's exactly what I wanted. There was no tendency to overshoot in attitude or overshoot in the selection of the landing site. I think all of this was because of the time that I had to work with the LLTV."]
[In a 1995 letter, Dave commented that he may not have been aware of the crater in which he put the rear pad because "it was shallow and probably had no shadow".]
[Scott, from the 1971 Technical Debrief - "I guess I can't say enough about that (LLTV) training. That puts you in a situation in which you appreciate propellant margins and controllability (because the vehicle could fail and crash). I think the LLTV is an excellent simulation of the vehicle. I think if you had to move from one point to another, you could do it quite well. I would recommend an altitude of at least 150 feet so you don't get into the dust problem. I think dust is going to be variable with landing sites."]
[Jones - "It seems to me that Jim's giving you a lot more LPD angles than I remember other LMP's giving the Commanders. And he doesn't give you a first H-dot (descent rate) until 500 feet, which is just before you go into P66. You two had obviously worked this final part many, many times."]
[Scott - "Oh, yes. And I wanted as much from Jim as I could get. I mean, I was outside the window. Everything from inside the cockpit was from Jim. So I had a lot of sources of information. We did that on the launch, too. We had everybody with a role talking to me. And sometimes simultaneously with the ground. And I remember having learned this from Jim McDivitt. Because he did this back on Apollo 9. To sort out the voices and take the one you wanted, and to get as much data as you could possibly have without an overload. You can block out what you don't want to hear. So when Jim and I worked on this, I remember we worked on him giving as much as he could, because I wasn't going to do any talking. I was going to do the flying. I was going to do outside the window, and he was going to tell me what was going on inside. We were comfortable doing it that way."]
[Jones - "You had rate meters and the like around the window, but you were entirely out the window."]
[Scott - "Entirely out the window. Because, from the LLTV training, keep it steady and you'll land it. I knew I could land the machine if it would stay upright and the engine kept burning. And all the other things I had was icing on the cake. So if Jim could feed me all this information, that was even better."]
[Jones - "So, basically, down to 400 or 500 feet, the computer's controlling the descent rate and you're basically just telling it where you want to put it down. And, below 500 feet, you take over and control the descent rate."]
[Scott - "Which probably gets you into the discussion of why people didn't use an automatic landing, like Jim Lovell would have. Lovell would have, he said, let the automatic system go. I don't know if you've had any other discussions on this point, but there were a lot. Because the automatic system would probably have done very well."]
[Scott - "I worked the rationale out with Jim (Irwin). The guy on the right's got to have some input 'cause, if the guy on the left screws up, it's bad news for the guy on the right. You know, if you're riding in the back of an airplane or in the right seat of an airplane, it's a lot more uncomfortable than if you have hold of the stick. And there are a lot of stories about that that are kind of interesting. But we sort of worked it as a team, because I could get all that data. My feeling was, if I'm in the loop mentally I can respond more quickly than if I have to watch an automatic system and take over and then get my mind in the loop. So I was more comfortable in flying a manual descent than an automatic descent. Not that I thought that the automatic descent wouldn't work. It would probably work. But, if something goes wrong, I'm in the loop already. And my mental computer is already running at full speed so, if there's a hiccup somewhere, I'm already on top of it. Whereas, if you have an automatic hiccup, you got to decide what it is you do to get into the system. That's why, in my opinion, I would always make the lunar landing manually. Mainly, because it's a challenge; but also because you (the pilot) are already on top of it and you're reaction to a failure or a problem is going to be much quicker. We were asked, 'Why don't you land automatically? Don't you think the system will work?' Of course, I think the system would work. But on the other hand, I think we - as a group flying the machine, the PGNS, AGS, Irwin, and me, we're all flying that thing - I think we as a collective entity are safer and more efficient if there's a focal point. And I was the focal point. Jim fed things into my ears. The Moon fed things into my eyes, and I could feel the machine operating. I had never heard a comparison with other flights, because we all left when we got through, right? I was very comfortable with Jim giving me as much as he could give me."]
[Journal Contributor Mike Poliszuk notes "Scott talks extensively about the time he spent looking inside vs. outside the cockpit. Had the technology been available at the time, a heads-up display (HUD) - window projected or projected onto a helmet-mounted display - would have been useful. At the minimum the LPD could have been displayed directly for the Commander, so the LMP would not have had to read the numbers aloud. Other data, such as h, h-dot, lateral rates could also have been projected; and with proper software, this data could have been portrayed in some graphical format that integrated all needed data into a form easily interpreted by the Commander."]
[Scott, in a 15 August 2009 e-mail - "I would much prefer to have Jim read the numbers rather than have anything else (other than the LPD) in the window to scan and interpret -- my job was to find a landing point, total focus on the surface, with no distractions in focus or observation. Heads Up displays are great for some things, but not for landing on the Moon....!! As a crew we had trained this way in many situations -- Al and Jim would fee me data and I would focus on the 'flying' at hand; this way I could use all of my inputs - including hearing - and they could use all of their outputs - seeing and speaking. As another example, the S-V launch required all three of us at max output/input, and, at least for us, it worked great, especially in sims when sim-supe was trying to wipe us out...!!.]
[Jones - "One of the things that Jack and Gene talked to me about was working hard on the AGS, not only as an abort system, but as...I don't want to misquote them, but to have confidence that they could have landed with it if they had to. They say that mission rules were, if the PGNS went out, you abort back to orbit. But they said they slogged the AGS pretty hard - with the updates and the like - that they felt fairly confident that they would have had good enough information out of it to land."]
[Scott - "I'll give you two comments. I was around when McDivitt and Schweickart spent a good portion of their lives on the AGS on Apollo 9. And it was not as capable as the PGNS. It was exactly what it was supposed to be - an abort guidance system. It was not as capable as the primary guidance system. But, from a technical, physical point of view, it would probably give you, in retrospect, enough information to make a manual landing from on the order of 400 or 500 feet. Just like an LLTV landing. If you can land the LLTV, then you could probably land on the AGS, because it would keep the system running. But, on the other hand, on a lunar mission, A, management would not let you do that. If I were a manager, I would not let you do that, because it's just not built to do that. And, B, when Jim and I were in our mission, we didn't ever consider that; we didn't spend any time on it. We were involved in other things and...Not that it wasn't a good idea because, when Gene and Jack got to their turn, things were much more mature, and they could spend time looking at that. And it's a good idea they did. And I believe they're right. The AGS probably could get you down. Nobody'd ever let you do it, though."]
[Jones - "You guys had been through your landing, John and Charlie had been through theirs..."]
[Scott - "And, as long as something will keep that vehicle stable...The LLTV landings were manual landings, and the LLTV was a great trainer. I mean, boy, am I glad we had that, because it gave me confidence that I knew what I was doing on the Moon, and I didn't have to think about things. I didn't have to consciously program myself to do things. I was automatic. So, my feeling was, if you can land the LLTV, you can land a LM. And if the AGS will just keep the sucker straight, you can get it down, manually. But you're not going to do that, mainly because, if you lose the PGNS, you're not going to land. That's the way it is. So you go into it that way. One of the things we did do was to cut the rendezvous in half, Jim and I. And they used it on 14, because our experience on Apollo 12 enabled us, when we got to 15, we were already up on the curve."]
["When you're in the simulator, and I'm sure Gene and Jack did the same thing, after a while you need some variety. I mean, there are all the normal emergencies and you can do all that stuff. So let's see what else we can do. Jim and I worked on cutting the rendezvous by one rev and helped them develop a quick rendezvous. And we got that done early on in 15, so they used it on 14. But I'm sure Gene and Jack, when they got in there, went through all their stuff. They were up on the curve, so 'Let's see if we can land on the AGS.' Great idea. Sure, you probably can. But we didn't do that."]
[Jones - "The LLTV. It was a solo vehicle. You didn't have an LMP standing there next to you feeding you information of any kind. What kind of instruments did you have?"]
[Scott - "Essentially the same as on the LM. Same kind of descent rate and altitude."]
[Jones - "Instruments surrounding a window?"]
[Scott - "Let me see. Yes, it was as high a fidelity as you can build on the Earth. You know, we started out with four LLTVs and ended up with one (because three were lost in crashes). And, every time one crashed, the hue and cry from management was, 'Get rid of those damn things, what good are they?' But we (astronauts), as a group supported the idea a hundred percent because, again, you've got to do things as real as possible before you get into the lunar situation."]
[In all, NASA built five LM trainers of this type. Two were an early version called the Lunar Landing Research Vehicle or LLRV. Neil Armstrong was flying LLRV-1 on May 6, 1968 when it went out of control. He ejected safely and the vehicle crashed. A later version was called the Lunar Landing Training Vehicle or LLTV and three were built. Two of these were lost in crashes on December 8, 1968 (piloted by Joe Algranti) and January 29, 1971 (piloted by Stuart Present). The LLTV was a more accurate LM simulator and Dave is correct in saying that only one was available in the months leading up to Apollo 15.]
[Scott - "I remember when Pete came back and I had a couple of conversations where I asked him, 'What do you think about the LLTV?' And he said 'Boy, that's the thing to have.' So, when my turn came, I was absolutely insistent. 'You've got to fly this thing.' I could probably have gone to the Moon and landed without doing it, but I certainly wouldn't have had the comfort or the confidence."]
[Jones - "Was the LLTV more or less stable than the LM itself?"]
[Scott - "Well, in what way? You couldn't abort. You run out of gas and you crash. And it also put you on the line. And it also enabled you to stretch yourself. In other words, when I flew the LLTV, I never landed it where I was supposed to land. When I got down to where I was comfortable I could go where I was supposed to go, I pushed myself on to a secondary landing point, so could learn how to do that. I never had to use it, but it was a great opportunity to push things out to the edge under a controlled situation, with supervision, with people watching you, on a normal day where you didn't have all these other things going on. So you could push yourself out there without taking a big risk. (See the LLTV Flight Rules.) And that's why I thought it was a marvelous machine. Hell of a challenge. A tough thing to fly. Landing on the Moon: I don't care what anybody says, that's damn hard. I mean, that takes real aviation. That's flying! And I think all the things we got prepared us to do that. And I was very comfortable."]
[Jones - "If you look at the list of Commanders, six of the seven (Jim Lovell included) assigned to make landings had Navy training. Everyone but Dave Scott."]
[Scott - "You're one of the first people I've ever heard observe that."]
[Jones - "And they had carrier experience. And Gene told me that he thought landing on the Moon was easier than a night carrier landing"]
[Scott - "And I think he's probably right. But go ahead."]
[Jones - "Had you ever done anything like that and is the fact that there were six Navy-trained guys due to the luck of the draw or did the carrier experience have anything to do with it?"]
[Scott - "Luck of the draw. Absolute luck of the draw. On the other hand, I think that they benefited from their carrier experience, because I do think it's hard. I've never done it but, golly, I know those guys real well and Dick Gordon (who was a Navy flyer) and I rotated backup and prime, backup and prime and we live across the street from each other and I flew with Dick a lot. Dick and I have lots and lots of yarns, together, let me tell you. And I know that the carrier landings at night are hairy mothers. They're tough. And I think that was valuable experience for those guys and I'd wish I had it. And I think it might have been tougher for me to learn how to land the LLTV without having had the experience of carrier landings. And I agree with Gene. Not that I can make a comparison from personal experience. But I can tell you that landing the LLTV was lot harder than landing any airplane I ever landed. But, as for who got to go, that was luck of the draw. As you well know...People say, 'Why did they pick Armstrong first? Oh, he was a civilian.' No, it was luck of the draw."]
[Jones - "He was in the rotation."]
[Scott - "One time, early on, Slayton put thirty guys in a room (members of the three groups of astronauts chosen in 1959, 1962, and 1963) and said 'You are the guys that are going to go to the Moon.' And that's even before we picked the Wordens and the Irwins (who were members of the group of 19 pilots chosen in 1966). They hadn't even been selected yet. 'You guys are going to go to the Moon. You've got it locked up, and we're going to put you in some order.'"]
["I looked at it one time because some of these discussions came up at dinner, somewhere, of all the guys who had an opportunity to land on the Moon because they were in the program at the point at which they could have. Less than fifty percent took it or really went and did it. (Fourteen members of the first three groups flew lunar missions. Jack Schmitt was the only one of six scientist astronauts selected in 1965 who flew a lunar mission. And nine members of Jim Irwin's group drew lunar missions). A lot of them left for, I think, funny reasons. Some of them (Ted Freeman, Charlie Bassett, Elliot See, Gus Grissom, Roger Chaffee, Ed White and, C.C. Williams) got killed. You look at the guy on the right of you and only one of you is going to get to do it. But the luck of the draw was the reason people got the missions they got. The fire came along, they changed the rotation, everything switched around."]
[Jones - "Mike Collins' neck problem (that knocked him out of the Frank Borman crew that flew Apollo 8), etc."]
[Scott - "So it was fortuitous, it really was, if you got into this string. You had to make your own way, because you had to do a good job. But one of the things I like is that nobody knew why they got selected. I mean, you couldn't work hard on this area, or you couldn't work hard on that person who happened to be in management. You had to just go and do the best you could do. And then be at the right place at the right time."]
[Jones - "I tell you, I love it that Deke has never talked about it."]
[Slayton did, however, eventually talk about crew selection in the excellent, posthumously-published book Deke!, written with Michael Cassutt, which appeared in 1994.]
[Scott - "And I think that's right. I think he shouldn't. I can tell you one exercise that's probably known. At one point when there were thirty, they got everybody in a room and they said, 'We want you to write down the names of who you think should be on the first lunar crew. We assume that you're going to write your own name, or you wouldn't be here. Therefore we expect you to write two names, and those are the two names that you would go to the Moon with.' Now, that's when you get down to serious selection. That's called peer review. When you're going to step off into something like that, you don't pick necessarily the good old boy who lives down the street. You pick the guy who you think could take care of you in that kind of situation. And I think that peer rating was a great idea. Whether they ever used it or not, I don't know. But I think it was probably a good start. And I think it's better that nobody ever tries to figure it out. Who cares? I mean, it's all done. Whatever they did, I think they did it right...(chuckling) of course. Why would I want to go any other way, right? I got mine, baby, so it must have been right!"]
[Journal Contributor Jack Kozak notes that, of the astronauts chosen to command Apollo missions, "in the class of 1959, Schirra and Shepard were Navy, but were the last of their class on flight status at the time of Apollo; the class of 1962 shows a perfect balance with three Navy (Conrad, Lovell, Young), one civilian (Armstrong, who was Navy trained), and three Air Force (Borman, McDivitt, Stafford); and the class of 1963 also balances perfectly with one Navy (Cernan) and one Air Force (Scott)."]
[Scott, from the 1971 Technical Debrief - "When Jim called a Contact Light, I pushed the Stop button, which had been in the plan. Knowing that the extension on the engine bell was of some concern relative to ground contact (the bell was ten inches longer than those on previous LM's to give improved engine performance and allow them to carry more equipment), it had been my plan to shut the engine down as soon as possible after Jim called the contact and to attempt to be at some very low descent rate, which we felt we were at that time."]
[According to the Apollo 15 Mission Report, their descent rate at Contact was 0.5 feet per second.]
[Scott, from the 1971 Technical Debrief - "The next event was the contact with the ground, which I guess was somewhat harder than the 1 foot per second. One of the sensations which helped me prepare (for the actual landing) was contact on the order of 1 foot per second, which feels rather hard with a tightly sprung system like you have on either of those two vehicles (the LM and the LLTV)."]
[At touchdown, their descent rate was 6.8 feet per second and they were drifting north at 1.2 fps and west at 0.6 fps. A quick calculation using descent rates of 0.5 feet per second at contact and 6.8 feet per second at touchdown indicates that Dave got the engine off at an altitude of about 4.3 feet and that they had a free-fall time of about 1.2 seconds.]
[Jones - "Do you remember the landing, itself?"]
[Scott - "Yes. Absolutely. Yeah, we hit firm. And one of the reasons - and Jim and I talked about it after we got down - of course, is that you don't know how it's going to feel when you land on the Moon until you land on the Moon. So I don't know what the other guys...I've never looked at the acceleration on touchdown. I don't know how to compare it. But it was a firm touchdown. One reason was, remember, we had to get the engine off. So, by golly, as soon as we got the contact light, the engine goes off. Another reason is we were the heaviest LM, so we're going to fall harder (but not faster) once we get the engine shut down. And another reason was we landed in that little crater, so when we touched down, we touched down probably one foot and then the other foot into the crater. So it was a firm landing, and Jim was probably surprised, not expecting it. I'm expecting it, because I'm flying it. And it's, again, the guy in the front seat versus the guy in the back seat. The guy in the front seat is tuned to what's going on, and the guy in the back seat isn't. So he'll be somewhat behind in the event. So what Jim was saying was 'Wow, we really had contact'."]
[Jones - "And his 'Bam'...The interval in there is long enough that it was the contact light, then the hit and his 'Bam'."]
[Scott - "And it surprised him. You know, whap, 'Bam'. But I'm in the loop. I know what's going to happen. He's calling these things, but he's not really in the loop. So it's a real surprise to him. Another interesting analogy is, in airplanes, in doing certain tests you do a lot of rolls. Test Pilots School is an example, when you went out and did many, many rolls, you never took anybody in the backseat, because they'd get sick. The guy in the front seat doesn't get sick, because he's doing it. The guy in the back seat gets sick. I don't care who you are. Some guys don't get sick anyway. But some of the real macho kind of guys who tell you 'You can't get me sick in an airplane.' Come along, fellow. I can get you sick; because I can do enough rolls in an airplane that I won't get sick in the front seat because I'm in the loop and I'm doing it, but the guy in the back seat will because he's not in the loop. It's the same kind of thing here. An instance of surprise."]
[Jones - "There's another Apollo example in the Rover driving on 17. Gene and Jack talked about it. Gene's driving. He's got the control handle, so he knows what he's going to do. If he's going to avoid a crater, he's got a little bit of warning. Jack doesn't."]
[Scott - "Same thing. The guy in the right seat has just got to hang on and hope, by golly, it works. Right?"]
[Jones - "What I read this morning, in the Mission Report, is that the plus-Z (west) and the plus-Y (north) footpads touched about simultaneously and then the minus-Y (south) and the minus-Z (east) went back into the crater and gave you the landed attitude."]
[They landed right over the northwest rim of a crater about 5 feet deep and 15 to 25 feet across and came to rest with the spacecraft titled back 6.9 degrees and to the left (south) 8.6 degrees. The main reason for shutting off the engine at Contact was to prevent a build up of pressure in the case that the engine bell came into contact with the ground. Because they landed straddling a crater rim, the bell did come into contact with the ground and, according to the Apollo 15 Mission Report, the buckling of the engine bell reported by the crew once they got outside may have been caused by a pressure build up, rather than the impact. The crater rim was quite soft and would have yielded instead of causing buckling of the bell.]
[Now that they are down, Dave, Jim and Houston will make sure that the spacecraft suffered no important damage during the landing and that it is safe to stay.]
[Scott - "As sort of a nuts-and-bolts thing, that's probably one of the tense times of the mission, right after you land. That's when you'll have a problem, if you have a problem. And the Stay is a relatively big deal, because everybody's looked at all the systems and they don't see anything major wrong. Up until that point, you're tuned to push the abort button. 'Cause if there's something radically wrong because of the landing, you got to get out of there. So that's a pretty tense thing where everybody's watching it closely. And it's always nice when they give you the Stay, because it's unlikely you're going to have a major problem after that."]
[Jones - "They look at the ascent stage and decide it's okay..."]
[Scott - "You're not going to fall over. There's always this...Part of the thing is, when you touchdown, if your rates - lateral and longitudinal - are too high, you could turn over. Not good. Or if you're in too big a slope. Or if a landing leg collapses. Or you're in a hole full of dust and you sink - you know, the Tommy Gold stuff. None of that happened, but you're tuned for it."]
[Cornell University physicist Thomas Gold had hypothesized that the Moon was covered with a thick layer of dust which would not support the landing of a spacecraft. Despite the presence of small craters -which would have quickly disappeared in a deep dust layer - in images returned by the Ranger and Lunar Orbiter spacecraft and the successful landings of several Surveyors on a very firm Moon, Gold's theory refused to go away completely, much to the annoyance of the astronauts and others.]
[The Flight Controllers in Houston see Dave and Jim turn the Engine Arm Off and the Flight Director tells the Controllers 'Okay, everybody keep their eye on it (meaning the LM).']
104:43:14 Scott: Okay. Landing Radar (circuit breaker)'s open. (Garbled) looks steady. (Pause)
104:43:20 Irwin: Okay, did you get the Landing Radar (circuit breaker) open?
104:43:23 Scott: Yup.
104:43:24 Irwin: Okay. (Pause) Standing by for T-1.
[T-1 is their first pre-planned opportunity to launch.]104:43:32 Scott: Rog.
104:43:35 Mitchell: Stand by. (Pause)
[The Flight Director polls the Flight Controllers.]104:43:40 Scott: Okay. Looks good on board.
104:43:46 Mitchell: Falcon, Houston. You're Stay (for) T-1.
104:43:51 Scott: Roger; stay for T-1. Okay. Let's get on with the (garbled) checklist. (Long Pause)
MP3 Audio Clip ( 2 min 56 sec )
104:45:02 Mitchell: Falcon, we have a Noun 43.
[Noun 43 is the memory location of the landing site coordinates calculated by the PGNS - latitude, longitude, and altitude above the mean lunar radius.]104:45:07 Scott: Okay. (Long Pause) Got the Pad for P12, Jim? (Long Pause)
[Program P12 would take them back to orbit, if necessary. In Houston, the Flight Director is told that the LM is tilted about 10 degrees off vertical; he is also told that the crew has loaded the P12 data properly.]104:46:38 Scott: See the little elevation in front of us there?
104:46:40 Irwin: (Inaudible)
[Jim appears not to be on voice-activated comm (VOX).]104:46:43 Scott: No, not out across the rille.
104:46:44 Irwin: (Faint) No, I mean...
104:46:46 Scott: Oh, hard to tell. (Long Pause)
104:47:15 Scott: No, we're not there (at the planned landing site). We're not too far from Salyut. I did find that. I think. (Pause)
104:47:25 Scott: One foot per second, too.
104:47:26 Irwin: (Faint) I know it! (Long Pause)
[Obviously, Dave and Jim are discussing the landing and where they might have landed. Salyut Crater was named for the small Russian space station then in orbit. Salyut 1 was launched on 19 April 1971 and Apollo 15 on 26 July.]104:48:33 Scott: (Responding to something Jim has said) Rog.
[Scott - "I've known a lot of the cosmonauts. My first meeting was at the Paris Air Show in '67, when Mike Collins and I had the first official meeting with cosmonauts. Pete Conrad and Gordon Cooper had run across a couple a year or so before at some IAF (International Astronautical Federation) meeting. And then we went to Paris. Long story. The NASA PAO (Public Affairs Office) guys said, 'Don't meet with the cosmonauts, they'll make you look bad.' But we did and had a good time - and they actually made us look good! I started to get to know them. I met them again at the Paris Air Show in '69. And, three weeks before we flew, they lost a Soyuz crew during re-entry, which created a disturbance about wearing suits and all that stuff."]
[The Soyuz 11 crew was launched to low-Earth orbit on 9 June 1971 and spent 23 days on board Salyut 1. On June 30, they made a re-entry in shirtsleeves and died of asphyxiation when their Soyuz sprang a leak at high altitude.]
[Scott - "We were sensitive to their program. We knew (Vladimir) Shatalov (Soyuz 4, 8, 10) and (Alexei) Yeliseyev (Soyuz 5, 8, 10) who were flying at that time and, later on, I got to meet them on the ASTP and got to know them very well. And, in that area, the Russians were being very aggressive. They were pressing the edge on a lot of things, and the competition was pretty hot. As you know now, they were preparing a lunar mission and, in fact, Leonov told me that in 1973 in his flat in Moscow. I got a fairly good story. He was going to be commander of the first lunar landing and the single guy to go down. We know all of that now, but nobody knew that then. But, at that time, it was hot and heavy competition. That's why we went to the Moon. Why did we go to the Moon? John Kennedy decided we had to beat the Russians. I'm glad he did."]
104:48:38 Mitchell: Falcon, Houston. You're stay for T-2.
104:48:44 Scott: (Responding with mock boredom) Okay. Stay for T-2. (Long Pause)
[Scott - (Laughing) "'Okay, all the hardware's over with. Let's get on with this.' Not to put it down. Once you're past T-1, it's unlikely you'll have any serious problems. So what we want to do is get all this stuff off and get on with why we're there (namely, the geology). But the procedures say, rightfully so, one step at a time, watch it carefully. Don't want to make a mistake."]104:49:20 Mitchell: Endeavour, Houston. Are you still with us?
104:49:26 Worden: Rog, Houston. Endeavour standing by.
104:49:29 Mitchell: Roger. Your buddies are on the ground, and we'll be along with you in a little while.
104:49:35 Worden: Rog, Ed. I listened to most of it. Could pick them up VHF all the way down, and, in fact, I just now lost contact with them.
104:49:44 Mitchell: Roger.
104:49:47 Worden: I had a beautiful view of the landing site going over, but I couldn't see anything. (That is, he saw no sign of the LM nor disturbance on the surface from the landing.)
104:49:52 Mitchell: We copy, Al.
[Long Comm Break]
[A detail from Pan Camera frame 9377 will be taken about four hours after the landing and shows the LM on the surface. The planned landing site just off the bottom of the detail, about 200 meters south of the southern rim of Last Crater. Stephen Tellier has provided a higher-resolution detail of the area immediately around the LM.]
[Scott - (Laughing) " I think during this period of time, we were talking about where we were. And we really didn't know where...I mean, we were on the Plain at Hadley. By the way, there's a reason for calling it the Plain. At my old school (West Point), the place where we used to have our parades was called the Plain. So at Hadley, we called it the Plain."]
[While they talk about where they landed, Dave and Jim are venting helium pressure from the descent-stage propellant tanks and are otherwise configuring the LM for the three-day stay. These procedures are listed on Surface Checklist page 1-1 and, as they go through the procedures, Houston follows along via telemetry.]
[In Houston, the Flight Director asks if the spacecraft tilt is acceptable and wants to review the relevant pre-flight assessments of the margins of safety.]
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