Как все ШЕСТЬ прилунений ЛМ пришлись на ПЛОСКУЮ поверхность?

[As mentioned previously, the engine bell is about ten inches longer than on previous missions. The extension was added to improve engine efficiency so that a heavier LM could be landed.]
[Jones - "Before I got the tape turned on, you said there was some lively discussion as to whether or not you'd be able to get the engine shut down fast enough."]

[Scott - "That was one of the big things for the Program Manager: could we get the engine turned off in time to land without buckling the engine bell, because it was an extended bell, almost down to the surface. If you didn't get it off, the gases would be pushed back up into the bell and split it. So one of the big things was to turn off the engine as soon as we got the contact. That's why the laughter there about 'Jim, did you ever see the contact?' And, also, because we landed 'firmly'. And that's why Joe is kidding me about the seismometers didn't record anything. And we all sort of know this inside kind of thing, because we had talked about shutting the sucker down and would it hurt to split the engine bell? Probably not, because we weren't going to use it again, anyway. But it becomes a matter of the aviators pride. 'By God, if the Program Manager thinks I'm going to split the bell, I'm not going to split it. We'll get that dude (shut) off right away.' As a result of that, we probably dropped in from ten feet and had this rather firm landing. And now we're sort of getting a little needle from Allen, which is okay. 'The seismometers didn't record it.' And asked Jim what he thought the velocity was. And it's a light-hearted, inside joking."]

[According to the Apollo 15 Mission Report, they were coming down at 0.5 feet per second (fps) at contact and 6.8 fps at touchdown. From these numbers and the acceleration of gravity at the Moon's surface, 5.3 feet per second squared, we can estimate that, from the time Dave got the engine shutdown, free fall lasted 1.19 seconds and that, during that time, the spacecraft fell about 4.4 feet.]

[Jones - "Are you aware that the engine bell did buckle? Do you remember seeing that?"]

[Scott - "I don't think it buckled."]

[Jones - "There's a picture."]

[Scott - "If I ever looked at it hard, I don't remember it because we got on to other things and it really didn't matter because we weren't going to use it again. But it would be interesting to see."]

[Jones - "It's Figure 7-1 (AS15-88- 11882) in the Mission Report."]

[Scott - "Oh, yeah. It's got a little wrinkle in it. I guess I owe McDivitt a dinner. I hope he doesn't try to collect."]

[The following is from the Apollo 15 Mission Report. "At touchdown, the lunar module was located partially inside a small crater with the rim of the crater directly underneath the descent engine skirt. The descent engine skirt buckled during landing. This...was expected as the skirt length had been extended 10 inches over that of previous vehicles. This buckling was noted by the crew and confirmed by photographs of the damaged skirt. The crew reported that there was a gap between the exit plane of the skirt and the lunar surface, indicating that the buckling was probably caused by a build up of pressure inside the nozzle due to proximity to the lunar surface, and not due entirely to contact of the nozzle skirt with the lunar surface. The crew also reported that the buckling seemed to be uniform around the skirt periphery and that the exit plane height above the surface was uniform."]

[The buckling suggests that, at touchdown, the bell came into contact with the ground and was at least partially closed, allowing hot gases still escaping from the engine to build up in the bell. The pressure could relieve itself in three ways: (1) by blowing away the soil sealing the bell; (2) by creating a vertical crack in the bell; or (3) by creating a circumferential buckling that would raise the lower part of the bell upward and create an escape path. The bell-like shape of the skirt - with the diameter decreasing upward - certainly made the latter mechanism possible and, indeed, this is what seems to have happened. It also seems possible that contact with the ground created a circumferential zone of weakness at the place where the buckling occurred.]

Post-SEVA Activities

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