posted 10-26-2010 03:16 AM               

A perfect landing resulted - about three feet above the surface, for upon engine shut down only the contact probes were touching the Moon and the LM dropped the last part.

posted 10-26-2010 02:40 PM            

This description of Apollo 17's landing according to Gene Cernan's autobiography 'The Last Man On The Moon' on page 319. "We dropped the last few feet with a stomach-flipping thud, jolted once and came to rest slightly tilted in a shallow depression."

In Andrew Chaikin's 'A Man On The Moon', on page 643 of author's notes Harrison Schmitt warned Cernan that his descent rate down to the last 25 feet was a "a little high" with some intensity in his voice to hint at his concern. He was later to say that, with a laugh, "Gene had an aggressive streak in his flying". Obviously he got it right for the last three feet.

posted 10-26-2010 03:33 PM               

The landing gear probes that have the "contact light" sensors at the tips, extend 6' below the footpads, which is the height the engineers who built the descent engine, thought would be a safe distance to shutdown. It was feared that if the engine was running while on the surface, there wouldn't be enough room for the exhaust to escape and could possibly result in an explosive blowback into the LM descent engine.

posted 10-26-2010 05:00 PM               

quote:

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Originally posted by Spacepsycho:
Conversely, the hardest landing was Apollo 16, where Duke shutdown the engine exactly at 6' and both astronauts thought the LM was going to tip over.

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Compare with Apollo 16 / Orion:

posted 10-26-2010 07:52 PM               

These notes are from the Landing section of the Apollo 15 Lunar Surface Journal:

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!"

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.

Scott - "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?"

Irwin, - "Yes, I agree."

posted 10-26-2010 07:54 PM               

quote:

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Originally posted by micropooz:
I never realized that there was so much impact damage on those landings.

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posted 10-27-2010 02:59 PM               

quote:

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Originally posted by Spacepsycho:
The photo of the Orion ascent module taken by Mattingly before docking, shows the damage to the back of the LM is worse than any other.

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quote:

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As far as the damage comparing 15 and 16 is not evidenced in the photos. Other than the AP15 engine bell hitting the surface, which was expected during the design phase, with the collapsing landing gear absorbing most of the energy (in theory).

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posted 10-27-2010 06:14 PM            

Point 2: I recommend "Digital Apollo" by David Mindell which discusses and compares all of the six landings. One of the points made by Mindell concerning the Apollo 15 landing was the enlarged descent engine-bell. Dave Scott was warned of the risk of "blow-back" if, for instance, the enlarged bell came down over a small boulder. This could have caused an explosion. As instructed, he cut the engine as soon as the contact light came on. He was descending at one foot per second when he cut the engine, but the longer fall increased the contact speed. As it turned out, it was just as well he followed orders. Mindell points out that the enlarged engine bell came into contact with the edge of a small crater, buckling it. (What if the engine had still been firing when the engine-bell connected with the ground?) I am in the happy position of having discussed the Apollo 15 landing with both Dave Scott (2008) and Jim Irwin (1983). I wanted to try to establish why the landing felt much more jarring than the other landings. [See "Footprints in the Dust", pp. 242-245]. The actual landing speed doesn't account for the jarring, since the landing legs should have absorbed the impact. When I discussed this with Dave Scott, we concluded, based on the photographs of the "terrain" and the buckled engine-bell, that "Falcon" made a five-point landing (i.e. the landing legs and the rim of the engine-bell) rather than the usual four-point landing. The landing forces would have been transmitted up through the structure of the spacecraft, thus reducing the shock-absorbing properties of the crushable landing-legs. Hence the jarring.

Each landing involved the risk of small craters and rocks being obscured from view by the flying dust. Al Shepard and Dave Scott ended up with legs in small craters, causing their LMs to tilt. If John Young had landed about ten feet back from his landing-point, he would have been into a deceptively steep crater and might have crumpled his engine bell on the rim. It wasn't as easy as they all made it sound!

By the way, Garymilgrom's enhanced photo only shows a small part of the engine-bell buckling on "Falcon." NASA image AS15-88-11882 shows the full amount of the buckling. Gary - can you brighten that image for us?