Section 9: Separation through LM Touchdown

Young: WeÂ’re just going to talk about the Lunar Module. Preparation for PDI was nominal, except we didnÂ’t have any comm.

Duke: We had to go to a different attitude than we expected, to maintain high gain. We never did get to see the ground.

Young: DPS/PDI Burn and Performance.

Duke: I think it was nominal. The radar locked on at 50,000 feet which is amazing.

Young: Let me say say something about that. As we were coming around the corner for PDI, we didnÂ’t have the high gain and our yawing was 20 degrees for the descent. Charlie says we were on the Omnis and we couldnÂ’t get lockup for the state vector that we needed to do PDI. About 12 minutes prior to PDI, Charlie suggested that we roll right 20 degrees. We rolled right 20 degrees, and it improved the comm margins considerably. I think itÂ’s something that everybody whoÂ’s going to work Omnis should think about, putting the Omni antenna toward the 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.

Duke: The engine worked just as advertised; throttle-down came right on prediction, and the profile we started high and to the south, about 16,000 feet high as a matter of fact.

Young: 16,000 feet high?

Duke: Yes, we started about 66,000 feet.

Young: And we were about 16,000 feet to the south also.

Duke: Right after throttle-down, we were back on standard profile.

Young: Yes, it was really beautiful.

Adequacy of Procedures and PGNS Performance during PDI was nominal.

Young: Spacecraft Trimming and Systems Status During PDI. Nominal.

Duke: Yes, a couple of things here, John. We didnÂ’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: Yes, and as a matter of fact, for any reasonable rendezvous or any reasonable landing, the COPS calibration and the LPD calibration are just something to take up time in the time line. Those things are done on the ground, and theyÂ’re done perfectly adequately, based on our experience. And it costs you gas too, because theyÂ’re 2 degrees per second maneuvers to get to them and they perturb the orbit.

Duke: IÂ’d just like to add a comment on it. If you consider trimming RCS maneuvers in the LM, thereÂ’s no question in the real world that the thing is 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, 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 no question in your mind which way youÂ’re going and which jets came on.

Young: The Radar Tracking Attitude was not as planned.

Duke: Not as planned because we were late doing the rendezvous radar checkout. But once we got the attitudes on that first rendezvous with Ken, the radar worked.

Young: That preparation for P01 was sort of off-nominal in that we had a wait and a Go for PDI. We had - was it two revs?

Duke: It was after the no circ burn.

Young: It was the third rev. Six hours. Okay, so it was three revs. During that time, we did a couple of P52s to keep the platform warm. In addition to the one that we did, we missed a rev of doing P52s in there somewhere. But there werenÂ’t any torquing angles. ThatÂ’s really a good platform.

Duke: There was no gyro drift compensation required no PIPA bias. In fact, we never had any update, even after sitting on the surface for 13 hours in power backup, they didnÂ’t change anything.

Young: The VHF Range was in good agreement with radar. The radar tracking attitude was right on, but we did it on the back side of the Moon just prior to the circ burn. The first one that we did, somehow, I didnÂ’t get a main load block. It was in the dark and I was pointed at the tracking light, but it wasnÂ’t like the usual tracking light. It probably had something to do with KenÂ’s attitude. I just got a very faint light out there, and I didnÂ’t have a main load block and I couldnÂ’t get a lockup. So we did another one for the rendezvous. We knew after weÂ’d run it for an hour and a half that it was going to work.

Duke: We had a pretty tough time with the high bit rate, due to the loss of steerable.

Young: Charlie, I donÂ’t know. They werenÂ’t getting lockup coming around the PDI; man, I was really sweating that when you said, roll, letÂ’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 that we needed, 12 minutes prior to PDI. I thought we were in trouble then.

Duke: Me, too. I thought it was really gone. The up-link was always clear, and we didnÂ’t have any garbled transmissions. So I had no trouble with the pads. The ground kept saying that we were really noisy, really horrible. So I used a louder voice. I know on Apollo 10, we had a couple of revs of that and itÂ’s really miserable trying to get things passed back and forth.

Young: We sure did, didnÂ’t we, come to think of it.

Duke: The only thing I can say on Attitudes and Position is that the pre-flight time line that we flew until circ, we did all those attitudes and maneuvers except for the one to the landmark tracking or viewing, and we had to get a high gain lock-on so we were pitched up and didnÂ’t see the landing site.

Young: Yes, if Ken had done the circ burn, we wouldnÂ’t have had any trouble doing PDI on that rev, so I think that the decision to cut a rev out of the time line was perfectly safe. It didnÂ’t work out and there may be other reasons why it wouldnÂ’t work out in the future, but if you think positively, thereÂ’s no reason the time line itself doesnÂ’t constrain it to doing the PDI after the first rev.

Duke: 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 time line was adequate and I recommend it for 17, if they plan to get out first.

Young: One thing in favor of getting out first is youÂ’ve already got your pressure suit on, and you donÂ’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.

The LPD Attitudes and Accuracy (Calibration). I think the LPD was perfect. I donÂ’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 be. cause according to our pre-flight maps, the north country was a little rougher. There were more contour lines up north than 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 donÂ’t remember how many there were. But at pitch-over, you could see (just like pre-flight) 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 wasnÂ’t as apparent. 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. ThereÂ’s just no doubt in your mind when youÂ’re at pitch-over, and the first thing you see was South Bay. There was some question about whether weÂ’d see the ray patterns at the low Sun angle, but thereÂ’s no doubt that we were seeing the ray patterns from South Ray at pitch-over, and thereÂ’s no doubt, at least in my mind, as to where that machine was flying to. And it was a simple matter to redesignate to the south and back up a hair.

Duke: WeÂ’d agreed that I was going to look out since I had two good craters on my side, and it looked just like the L and A.

Young: In fact, it was working so well I was tempted to let it 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. 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 of my window, I could see that crater down there, so I went forward a little bit and landed. I counted one-potato after we got the contact light and shut the engine down; even so, I think that we fell about 3 feet. I think weÂ’re very fortunate that the landing was so flat because I really couldnÂ’t judge the slopes. We just lucked into almost zero roll and a couple of degrees or 3 degrees pitch-up, and of course weÂ’d taken the yaw out. When we redesignated to the south, we must have had 30 degrees of yaw and took it back out. Like I say, at that Sun angle, we could see the rocks all the way to the ground and I think that was a great help. From 200 feet on down, I never looked in the cockpit. It was just like flying the LLTV; your reference is to the ground outside. You had another thing that nobody has ever remarked about before, and that was the shadow. really didnÂ’t have any doubt in my mind how far above the ground we were with that shadow coming down. 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 the guesswork out of it. For that kind of a Sun angle, if the radar had crumped, I donÂ’t think youÂ’d have had a bit of trouble in just going right in and landing just like a helicopter. First, we could see the thing up 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 youÂ’re hovering, there wasnÂ’t any doubt in my mind that I was hovering. I could look out the window and see that weÂ’re hovering just like a helicopter. We were well into the dust, maybe 140 or 50 feet off the ground, when weÂ’re doing that.

Change in Appearance of Features, Distance Estimation of Landmarks. I think because we practice so much with the L and A, we had a pretty good hack on how far away we were from things. And the only change I'd make (and I donÂ’t know how much of a change it is) is that after we got out and went up on Stone Mountain and looked back, you could see Double Spot and you could see the Lunar Module, and it looked as if we were maybe 70 or 80 meters further east than I said we were originally. ThatÂ’s just a guess because weÂ’re sitting up north on a hill and looking back, and you could see Double Spot. And the Lunar Module appeared to be sitting in a hole over behind Double Spot, and itÂ’s almost in a direct line from where we were on Stone Mountain. So we must have come very close to landing exactly where we were scheduled to land in the first place. And I emphasize again, the only reason for landing there was to get a spot that wasnÂ’t so hilly. Pre-flight, that region around Double Spot was the only flat place on the map as far as the contour lines go. I think it was a mistake.

Duke: It turned out, I think, the flattest spot that we saw on the whole traverse was up to southeast of North Ray Crater in that valley past Palmetto. It was a broad smooth valley and hardly any craters in it at all. No rocks.

Young: No rocks at all, and on the contour map, that looks pretty bad.

Duke: But it was about where Dog Leg was mapped, in that area, back off to the right there by the traverse. I had a good feel at pitch-over of exactly where we were; once we got to the ground and I looked out JohnÂ’s window, I felt like I could reach out and touch South Ray and Stone Mountain. They just looked that close to me. I had a tough time estimating and I knew they were 5 kilometers away- and I just had a tough time estimating distances of big features, once we got on the ground.

Young: On a clear day, the mountains are 40 miles away and it looks like youÂ’d be there in 4 minutes. ItÂ’s the same thing On the Moon. We kept going over rises and I kept thinking, hereÂ’s Stone Mountain; and then weÂ’d go over another, and it wouldnÂ’t get you there.

Duke: There were lots of ridges between us and that mountain. It wasnÂ’t apparent when we first looked out the window.

Young: I know people have remarked on this before, but thereÂ’s a lot more light in that vehicle than there is in the Lunar Module Simulator. I donÂ’t know why they want to keep it so dark in there, but we didnÂ’t have any trouble reading any of the gages. Sometimes we get in the LMS and everything is all turned out in there, and itÂ’s just like normal light. We never did have any trouble seeing any of the instruments. My subjective opinion of the light produced by those utility lights was much better than it is in the simulator.

Duke: In the dark, we had the integral lighting up and the side panels on, and that was about all you needed.

Young: I couldnÂ’t judge slope out the window worth a hoot, and thatÂ’s the truth, even down low. The ground looks flat but IÂ’m sure it would look flat if it had been a 6- to 8-degree slope too. I donÂ’t see any way around that. IÂ’ve done a lot of helicopter flying, looking at slopes and you canÂ’t judge slopes in a helicopter from 100 feet on down very well either. And thatÂ’s the way it is. But I donÂ’t think youÂ’d be in any trouble if you touched down within 10 or 15 degrees of being straight up and down. ItÂ’s going to bother you some in deploying gear off the lunar module, but it isnÂ’t going to bother your performance.

Hovering and Blowing Dust. We did a hover for a short period of time there at about feet off the ground, and the rates were practically zero and there was blowing dust.

Duke: It started at about 80 feet, John.

Young: 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 and with something like that - which really surprised me. I was expecting two things: either the dust would be so bad we couldnÂ’t see anything, or there probably wouldnÂ’t be as much dust as there was. Possibly, itÂ’s the 15-degree Sun angle that did all that. Because thereÂ’s certainly plenty of dust down there to blow, and thereÂ’s nothing thin about that regolith around the LM.

Duke: How about that Zero Phase? I never noticed it.

Young: First, the thing starts out as a Sun coming and that turns to a shadow. That was zero phase getting better all the time.

Duke: I was excited at that time.

Young: Yes. When you said, here comes the shadow, that was before I had seen it. In fact, you were watching it out your window and I looked up there and I saw it, and I said, "Yeah, man thereÂ’s no doubt", and that baby got bigger and bigger and dropped right down in front of us, and man, thatÂ’s a good gage.

Duke: Was it?

Young: Yes, we saw it in a film.

Duke: It looked just like that one in the LMS.

Young: I donÂ’t know if you know this, Deke, they had a shadow for us, and I guess weÂ’ve been using it. In fact, weÂ’d been practicing 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 youÂ’re at 100 feet and you have 20 feet a second down, if you go to full throttle, youÂ’ll have that all killed before you hit the ground. So weÂ’re looking at very high sink rate descents off-nominal with the shadow. Man, it really makes a difference when youÂ’re looking for it. A crater from 50,000 feet looks like a crater at 5 feet, thatÂ’s the bad part of it. But with a shadow, as it gets bigger, you know youÂ’re getting closer.

Duke: When the computer said level off, we leveled off at about 40 feet off the ground. I think you had a good feel that it was leveled oft. There was no question in your mind that youÂ’d stopped coming down. I remember seeing them at about a minus 0.7.

Young: And then we pitched forward again. I didnÂ’t want to go backwards at all.

Duke: But the needles were great.

Young: And from looking at the probes, we must have come pretty much straight down.

Duke: Every one of them had folded straight up.

Young: Significant Impact and Vertical Motion Sensations. 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 donÂ’t know how much we were coming down, maybe a foot a second.

Duke: I donÂ’t remember exactly, but about 1.8, I think I saw, right before touchdown.

Young: Engine Shutoff and Probe Contacts Pad Cue.

Duke: Dave had the same slow descent too, and they had the same sensation that when you shut the engine down, the LM really free falls. I think a softer landing would be a 3-foot-a-second descent and allow the tailoff to cushion you as you continue down because the gravity really had us. I had a definite sensation of falling when you shut down.

Young: I donÂ’t see what youÂ’re talking about. If you got 3 feet a second and you fall when you shut the engine off ...

Duke: If youÂ’re leveled off, 5 feet above the ground and stopped the engine, I think youÂ’ll accelerate faster than if you came down at 3 feet a second when you got contact and just kept coming at 3, then that 3 feet a second is constant. And by the time you can shut the engine down, youÂ’ve already hit the ground at a 3 feet a second versus the gravity acceleration type fall.

Young: IÂ’m not sure thatÂ’s true.

Mattingly: Seems like the only way that could be softer is if youÂ’re saying the engine would be running when you hit the ground.

Duke: Yes.

Young: You could do the same thing by waiting a little longer to shut the engine down.

Duke: ThatÂ’s right.

Young: With all those bloody rocks around there, I don’t see — we had a lot of choice. Just want to make sure you were on the ground.

Duke: Yes, itÂ’s a definite warmth, but thereÂ’s no doubt that the LM can hack it.

Slayton: Did you get any stroking of any of the struts?

Young: I donÂ’t feel that there was because that first step was a biggy.

Mattingly: You were talking about if you back into that crater behind you, and that gear is only going to help you if you can stroke it, isnÂ’t that right? It seems like thereÂ’s some advantage to hitting the ground hard.

Young: No, Ken. I wouldnÂ’t stroke that gear, man. IÂ’ll tell you, that would really jar your teeth. IÂ’d. rather have them cut off a couple feet just to get me closer to the ground. IÂ’m only talking about the slope.

Duke: If you land on the upslope, the rear gear as you fall down could very well stroke.

Young: If the rear strut had been over that hole, weÂ’d have been just like the Apollo 15 guys. We would have been landing on the first 3 and the engine bed. It really dropped.

Duke: We had about 1 percent on the fuel and 6 percent on the oxidizer, and we had just gotten a descent warning light. Things never matched up the whole way down. They were running 2 to 3 percent low on the oxidizer side.

Young: We had 4 percent fuel and 6 percent oxidizer. That 1S about a minute of hover time or better.

Duke: I remember their saying Descent 1, and the quantity light was on when I looked up to check the systems after shutdown. I donÂ’t remember their saying a minute, giving us any call.