MoonTraveller recognizes the passing of astronaut Neil Armstrong, who together with Buzz Aldrin, landed on the Moon in July of 1969. Neil is pretty busy in this landing audio, Buzz is reading-out the computer telemetry etc, and Neil is focused, but this NASA transcript includes debriefing commentary (what he was thinking) and later historical reminiscences by Neil. On touch down he says "Engine arm is off. Houston, Tranquility Base here. The Eagle has landed."
He had the Midwestern pilot drone attitude down cold. Uninterruptible, he was thinking, and going to land this thing come hell or high water. Before the moon he was a famed test pilot. His coolness when a prototype model LEM blew up [he ejected] was part of his legend. From this transcript I detect a call out that I take it as his descent engine had 30 sec of fuel left about 26 sec before he landed.
The press asked questions. He'd laconically respond. Actually, he was thinking. Tom Wolfe: "You'd ask him a question, and he would just stare at you with those pale-blue eyes of his, and you'd start to ask the question again, figuring he hadn't understood, and— click —out of his mouth would come forth a sequence of long, quiet, perfectly formed, precisely thought-out sentences."
Neil Armstrong of few words the size attained of a tech folk hero immense. The stores of the day sold models, toys, space cards, astronaut on the moon draperies for children's bed rooms. Thought: Will there come a day when no one walking the earth has walked on the Moon?
RIGHT CLICK HERE TO SELECT 'OPEN NEW TAB' TO HEAR HISTORIC RECORDING
102:44:07 Aldrin: 250 (feet altitude), down at 2 1/2, 19 forward. (Pause)
102:44:13 Aldrin: Altitude (and) velocity lights (on).
[This warning light indicates that the computer is not getting good radar data. Paul Fjeld adds, "The radar lost track with the surface twice after Neil took over manual control: once nearly a minute into P66 for 20 seconds and then, for a few seconds, about 40 seconds before touchdown."]
102:44:16 Aldrin: 3 1/2 down, 220 feet, 13 forward. (Pause)
[The onboard recording can be found at Mike Smithwick's Apollo 11 Audio site. Access the onboard clip by clicking on the yellow ">" for Day 5 - Landing. the onboard is item 3 on the menu that appears. the clip starts at 102:31:49.]
102:44:23 Aldrin: 11 forward. Coming down nicely.
102:44:25 Armstrong (onboard): Gonna be right over that crater.
[The crater Neil mentions is about 60 meters east of the spot where he will land and is known as Little West Crater]
102:44:24 Aldrin: 200 feet, 4 1/2 down.
102:44:26 Aldrin: 5 1/2 down.
102:44:29 Armstrong (onboard): I got a good spot (garbled).
102:44:31 Aldrin: 160 feet, 6 1/2 down.
102:44:33 Aldrin: 5 1/2 down, 9 forward. You're looking good.
102:44:40 Aldrin: 120 feet.
102:44:45 Aldrin: 100 feet, 3 1/2 down, 9 forward. Five percent (fuel remaining). Quantity light.
[Fjeld - "The quantity light latched at 102:44:31, and indicated that 5.6% of the original propellant load remained. This event started a 94-second countdown to a 'Bingo' fuel call which meant 'land in 20 seconds or abort.' So if the count gets down to zero, Neil will have 20 seconds to land, if he thinks he can get down in time. Otherwise, he will have to abort immediately. If you're 50 feet up at 'bingo fuel' with all of your horizontal rates nulled and are coming down to a good spot, you could certainly continue to land. With your horizontal rates nulled at 70 to 100 feet, it would be risky to land - perhaps giving you a landing at the limiting load of the landing gear. At anything over 100 feet, you'd punch the abort button, say goodbye to the moon, and stew for the rest of your life!"]
[The Descent Quantity Light - labeled DES QTY - is one of a group of twenty warning lights ( 94k ) at the top of Panel 1, which is to the right of the CDR's window. In a 2006 exchange of e-mails, Frank O'Brien indicated that these warning lights were amber on the simulators at the Cradle of Aviation Museum; Ed Mitchell confirmed that they were amber on the flight LMs; and Dave Scott added, "Probably amber. 'Red was for emergencies'. We spent considerable time with the contractors defining the color, title, and placement of C&W lights"]
102:44:54 Aldrin: Okay. 75 feet. And it's looking good. Down a half, 6 forward.
102:45:02 Duke: 60 seconds (of fuel left before the 'Bingo' call).
[The accompanying 16-mm film clip (4.0Mb) by Gerald Megason covers the last forty seconds of the descent. The camera was mounted in Buzz's window and, when the clip starts, Little West Crater is visible at the bottom of the window.]
102:45:04 Aldrin: (Velocity) light's on.
[Fjeld - "This is a result of a second, brief radar dropout."]
102:45:08 Aldrin: 60 feet, down 2 1/2. (Pause) 2 forward. 2 forward. That's good.
[Neil wants to be moving forward as he lands so that he can be sure of not backing into an unnoticed or forgotten hole behind him.]
102:45:17 Aldrin: 40 feet, down 2 1/2. Picking up some dust.
[Armstrong, from the 1969 Technical Debrief - "I first noticed that we were, in fact, disturbing the dust on the surface when we were something less than 100 feet; we were beginning to get a transparent sheet of moving dust that obscured visibility a little bit. As we got lower, the visibility continued to decrease. I don't think that the (visual) altitude determination was severely hurt by this blowing dust; but the thing that was confusing to me was that it was hard to pick out what your lateral and downrange velocities were, because you were seeing a lot of moving dust that you had to look through to pick up the stationary rocks and base your translational velocity decisions on that. I found that to be quite difficult. I spent more time trying to arrest translational velocity than I thought would be necessary."]
102:45:21 Aldrin: 30 feet, 2 1/2 down. (Garbled) shadow.
[What Buzz says here is sometimes transcribed as "Faint shadow" but I recently listened, once again, to both the Public Affairs tape and to the onboard tape and feel uncomfortable making a decision, primarily because the transmission is distorted and partially clipped. Buzz first saw the LM shadow when he looked out at 102:44:04, a fact which adds to my discomfort with the usual transcription. In 2006 I listened to the HSK recording of the Net 1 feed from Goldstone and am still not able to make a decision.]
[Fjeld - "Perhaps Buzz did say 'Faint shadow' but was referring to the now fuzzy edge of the shadow on the streaking dust layer."]
[David Harland suggests a transcription of 'Great shadow', but I still do not believe it is possible to definitively pull this one out of the noise.]
102:45:25 Aldrin: 4 forward. 4 forward. Drifting to the right a little. 20 feet, down a half.
102:45:31 Duke: 30 seconds (until the 'Bingo' call).
102:45:32 Aldrin: Drifting forward just a little bit; that's good. (Garbled) (Pause)
[Armstrong, from the 1969 Technical Debrief - "As we got below 30 feet or so, I had selected the final touchdown area. For some reason I'm not sure of, we started to pick up left translational velocity and a backward velocity. That's the thing I certainly didn't want to do, because you don't like to be going backwards, unable to see where you're going. So I arrested this backward rate with some possibly spasmodic control motions, but I was unable to stop the left translational rate. As we approached the ground, I still had a left translational rate which made me reluctant to shut the engine off while I still had that rate. I was also reluctant to slow down my descent rate anymore than it was, or stop (the descent), because we were close to running out of fuel. We were hitting our abort limit."]
[Armstrong - "I guess that, at that altitude, running out of fuel wasn't a consideration. Because we would have let it just quit on us, probably, and let it fall on in."]
[Fjeld - "An engine cut-out at any height above 10 feet would have produced a touchdown harder than the landing gear was designed to withstand."] [On 19 September 2001, Neil was interviewed at NASA Johnson by historians Stephen Ambrose and Douglas Brinkley as part of the JSC Oral History project. During that interview, Neil said, "I wanted to make it as easy for myself as I could on that first (landing)—there's a lot of concern about coming close to running out of fuel, and I was very cognizant of that. But I did know that if I could have my speed stabilized and attitude stabilized, I could fall from a fairly good height, perhaps maybe forty feet or more in the low lunar gravity, (and) the gear would absorb that much fall. So I was perhaps probably less concerned about it than a lot of people watching down here on Earth. That's not to say I wasn't thinking about it, though, because I certainly was, but I thought it was important to try to get it down smoothly on the first try. We didn't know how that landing was actually going to go until that point. So I wanted to make it as gentle as I could."]
[In an e-mail response to a question from Journal Contributors Matt Gleason and Larry Jordan, Neil elaborated: "When my eyes tell me I am about 40 feet (12 meters) above the ground, the landing footpads are about 24 ft above the surface. The impact velocity under lunar gravity would be the square root of 2gh (two times the lunar gravitational acceleration {g} multiplied by the height {h}) or about 16 feet/second (5 m/sec or 17.5 km/hour). That should be acceptable. Uncertainties include the residual thrust of the descent engine as it runs out of fuel, the softness of the lunar surface, and the additional energy absorption of the landing legs and engine nozzle if the descent rate exceeds the gear design limit, and how much safety factor there is in the honeycomb crush calculation. They all should be favoring a safe impact."]
["It's only a barnyard calculation, but I probably could not judge 40-foot eye height well with all the blowing dust. But I would certainly prefer that drop to trying to go through the abort sequence at that altitude."]
[More commentary on the translational velocities follows the landing.]
102:45:40 Aldrin: Contact Light.
[At least one of the probes hanging from three of the footpads has touched the surface. Each of them is 67 inches (1.73 meters) long. The ladder strut doesn't have a probe. Buzz made the call at 20:17:40 GMT/UTC on 20 July 1969.]
[Aldrin - "We asked that they take it off."]
[Journal Contributor Harald Kucharek notes that Apollo 11 photo S69-32396, taken on 4 April 1969, shows Eagle with a probe attached to the plus-Z footpad. This indicates that the probe was removed after that date. The probe attachment is highlighted in a detail.]
[Apollo 11 photograph AS11-40-5921 shows the area under the Descent Stage. A gouge mark made by the probe hanging down from the minus-Y (south) footpad is directly under the engine bell, a graphic demonstration that the spacecraft was drifitng left during the final seconds.]
[Armstrong, from the 1969 Technical Debrief - "We continued to touchdown with a slight left translation. I couldn't precisely determine (the moment of) touchdown. Buzz called lunar contact, but I never saw the lunar contact lights."]
[Aldrin, from the 1969 Technical Debrief - "I called contact light."]
[Armstrong, from the 1969 Technical Debrief - "I'm sure you did, but I didn't hear it, nor did I see it."]
102:45:43 Armstrong (onboard): Shutdown
102:45:44 Aldrin: Okay. Engine Stop.
[Neil had planned to shut the engine down when the contact light came on, but didn't manage to do it.]
[Armstrong, from the 1969 Technical Debrief - "I heard Buzz say something about contact, and I was spring-loaded to the stop engine position, but I really don't know...whether the engine-off signal was before (footpad) contact. In any event, the engine shutdown was not very high above the surface."]
[Armstrong - "We actually had the engine running until touchdown. Not that that was intended, necessarily. It was a very gentle touchdown. It was hard to tell when we were on."]
[Aldrin - "You wouldn't describe it as 'rock' (as in, 'dropping like a rock'). It was a sensation of settling."]
[Some of the other crews shut down 'in the air' (meaning 'prior to touchdown') and had a noticeable bump when they hit.]
[Aldrin - (Joking) "Well, they didn't want to jump so far to the ladder."]
[Readers should note that, although the Moon has no atmosphere, many of the astronauts used expression like 'in the air' to mean 'off the ground' and, after some thought, I have decided to follow their usage.]
[Armstrong, from the 1969 Technical Debrief - "The touchdown itself was relatively smooth; there was no tendency toward tipping over that I could feel. It just settled down like a helicopter on the ground, and landed."]
[On a final note about engine shutdown, Ken Glover calls attention to the following from an interview done with Neil on 19 September 2001 by historians Stephen Ambrose and Douglas Brinkley at NASA Johnson.]
[Brinkley: "Was there anything about your Moon walk and collecting of rocks and the like that surprised you at that time when you were on the Moon, like, 'I did not expect to encounter this,' or, 'I did not expect it to look like this'? Or included in that, the view of the rest of space from the Moon must have been quite an awesome thing to experience."]
[Armstrong: "I was surprised by a number of things, and I'm not sure (I can) recall them all now. I was surprised by the apparent closeness of the horizon. I was surprised by the trajectory of dust that you kicked up with your boot, and I was surprised that even though logic would have told me that there shouldn't be any, there was no dust when you kicked. You never had a cloud of dust there. That's a product of having an atmosphere, and when you don't have an atmosphere, you don't have any clouds of dust."]
["I was absolutely dumbfounded when I shut the rocket engine off and the particles that were going out radially from the bottom of the engine fell all the way out over the horizon, and when I shut the engine off, they just raced out over the horizon and instantaneously disappeared, you know, just like it had been shut off for a week. That was remarkable. I'd never seen that. I'd never seen anything like that. And logic says, yes, that's the way it ought to be there, but I hadn't thought about it and I was surprised."]
102:45:45 Aldrin: ACA out of Detent.
102:45:46 Armstrong: Out of Detent. Auto.
[Armstrong, from a 1996 letter - "The Attitude Control Assembly [ACA] was the control stick. It had potentiometers or transducers or something similar to provide an output proportional to stick position. Output went to the LGC (LM Guidance Computer) to command the RCS jets to fire. 'Out of Detent' simply means the stick was moved away from its centered position. It was spring/detent centered like the turn signal control on your car."]
[Fjeld - "Because the Digital Autopilot (DAP) was in Attitude Hold, it was firing the jets like mad at touchdown to maintain the pre-touchdown attitude. By joggling the ACA, a new reference attitude was sent to the DAP. Since they weren't moving anymore, the new attitude needed no jet firing to maintain. Soon after, the DAP was cycled with the P68 landing confirmation program."]
102:45:47 Aldrin: Mode Control, both Auto. Descent Engine Command Override, Off. Engine Arm, Off. 413 is in.
['413' is an AGS address and has been a topic of considerable interest to Journal Contributors Marv Hein and Frank O'Brien. Frank supplied the following description.]
[O'Brien - "(The AGS is) a wonderful machine. If you have done any work on a computer that just has a switch register and display (such as an IMSAI, ALTAIR or one of my favorites, the KIM-1), you'd be comfortable with the AGS."]
["The way the AGS operated is that you had only an address and data display, 0-9 keypad, a Clear button, plus +/-, Enter and Readout. That's it. The ultimate in simple interfaces! How the AGS was operated was to press Clear, then a memory address. On a 5-octal character display, you got what was stored in that location. To change it, you typed a +/-, followed by 5 characters. Pressing Enter stored the value directly into memory. What you hear is the checklist item noted as: 413+10000. The key sequence is Clear, 413, Enter, +10000, Enter."]
["Address 413 contains the variable that indicates that the LM has landed - so any abort will be from the surface - which further tells the AGS to save the attitude information from its gyros. These gyros were 'strap-down' types, which means that they had a fixed orientation with respect to the LM body. They also had a nasty habit of drifting quite a bit. So, as soon as they landed, the AGS was to 'lock in', if you will, the attitude the LM was in. If the PGNS died - and it was the PGNS that oriented and re-aligned the AGS - at least they would have some approximate attitude information to abort with."]
102:45:57 Duke: We copy you down, Eagle.
102:45:58 Armstrong (onboard): Engine arm is off. (Pause) (Now on voice-activated comm) Houston, Tranquility Base here. The Eagle has landed.
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