Landing the LM

[lukepemberton]

I'm sure that landing the LM has been discussed at the boards recently, and it was in the hoax section. What I'm really interested in is how they controlled the LM to the surface, and I'm sure the flight path and use of the engine was discussed in great detail.

Does anyone recall the discussion and where the OP is? I think it was in response to Rodin, but I cannot find it.

Thanks in advance.

Luke

[carpediem]

I recall this thread started by Hunchbacked:
apollohoax.proboards.com/index.cgi?board=theories&action=display&thread=3011&page=1

[lukepemberton]

Jul 10, 2011 14:42:25 GMT -4 carpediem said:

I recall this thread started by Hunchbacked:
apollohoax.proboards.com/index.cgi?board=theories&action=display&thread=3011&page=1

That's the link. Many thanks.

[ka9q]

Do you know about the Apollo Experience Reports? At least one of them is about lunar descent techniques.

[zakalwe]

I'm currently reading Digital Apollo which is a cracking book. There's plenty of detail (from a LGC point of view) in there.

[Obviousman]

Yeah, the NTRS is fantastic. Just do a search for lunar module, downloadable documents.

[Obviousman]

BTW, what are you interested in? I learnt a bit about the various programs they used, when they switched over, etc, during my various researches. If you have a specific question, I'm happy to try and answer it.

[Kiwi]

Luke, have you read the first chapter of all the Apollo Lunar Surface Journals? There you get technical info about the powered descent and landing, and comments from the astronauts, along with input from other knowledgeable folk.

One thing I did for my own information was check out the ground track of Eagle's powered descent, which I listened to live on the radio when it happened. It started above or just after they passed above Mount Marilyn, which got its name from Jim Lovell's wife.

You can see Mount Marilyn on any good photo of the moon that shows the two Messier craters. It's a light-coloured T- V- or Y-shaped (depending on the contrast) lone mountain on the dark mare at about 4 o'clock (when north's at the bottom) from Messier and Messier A, the two craters which have the very long tails. Its coordinates are approximately 40 degrees 0 minutes east, 1 degree 30 minutes north and in close-ups it has a distinct crater on its northern arm.

Good photos of it are AS10-28-4165, AS10-30-4437 and AS10-31-4521 (Kipp Teague's site, www.apolloarchive.com
from memory).

[lukepemberton]

Thanks for the replies. I'll have a read over the weekend.

[Apollo Gnomon]

Once again a hoax theorist has said something that's basically stupid but raises an interesting question. In this case it relates to the Apollo 11 LM being "lost" on the surface.

My question is: Could the LM actually land so far off target as to make orbital rendezvous with the CSM impossible? Or do the LM Ascent Stage and CSM have enough maneuvering fuel between them to hook up even if the LM were to land in a completely random spot?

So the question falls into several variables --

1) how far off target could the LM manage to get? Latitude would be worse than longitude, as I understand it, so how much latitude shift could an LM manage during deorbit?

2) How far out of proper orbit would the CSM have to get to be unable to perform a Trans Earth Injection burn that puts them back to the Earth in any useful way?

I don't have Orbiter installed anymore, but that's how I would figure this out.

Any help on this one?

[ka9q]

Aug 27, 2011 15:01:33 GMT -4 Apollo Gnomon said:

Once again a hoax theorist has said something that's basically stupid but raises an interesting question.

Yup. That's the main reason I still engage in this stuff; I learn a lot in the process of answering hoax claims even if the hoaxers don't.

My question is: Could the LM actually land so far off target as to make orbital rendezvous with the CSM impossible?

Not really. Think about it: the LM moves in the same orbital plane as the CSM, so any landing error has to be along the orbital track. That was the case for Apollo 11 when they landed past their intended target.

As long as they know where they are relative to the CSM, they can simply adjust their launch time to put them in the correct position relative to the CSM after reaching orbit. The rendezvous radar is designed to give them exactly this information. I'm pretty sure it was regularly used from the surface a revolution or two prior to ascent to refine their relative positions.

[echnaton]

So there is no way the LM could get seriously out of plane?

It is an interesting question. My speculation is that the out of plane error would be noticed before it became serious and a well before landing. At that time the landing would be aborted.

But what if the LM went wonky and made a burn on some random heading at the worst possible time? What ever the worst possible time would be. Perhaps a failure in the descent stage that couldn't be stopped and required an emergency assent stage separation? There could be a random out of plane error with little knowledge of its extent and a limited time and fuel budget to recover. Could the abort systems have handled that?

While all hypothetical, it seems possible and something that I am sure was thought about. And another good reason to think about the courage those guys had.

[ka9q]

It's hard to see how the LM could have gotten seriously out of plane without squandering so much delta-V that it wouldn't be able to land at all. It's not like they had a lot of fuel margin to begin with, and plane changes are notoriously expensive.

Two inertial reference systems are continuously monitoring the actual motions of the LM, so even if something had gone haywire with the steering the computers would still have a pretty good idea of the resulting orbit.

Yes, abort limits were carefully drawn in advance to maximize the probability of surviving any given failure. There were abort limits even on landing errors in the up/down track direction, though they were much looser than in the crosstrack direction. That was one of the big concerns during the A11 landing.

[echnaton]

I would be interesting from a historical perspective to know how much work was done on this in planning for the missions and what the contingencies were. They planned for so many things that could go wrong, but was there a point in a malfunction scenario (however unlikely) in which an out of plane error was considered unrecoverable? The engineering fanboy in me always wants to know these things.

[ka9q]

About the only way to put them far out of plane would be a serious undetected yet correlated failure in both navigation systems, which seems extremely unlikely. As long as nav is working, they'd know they were out of plane and keep it from happening in the first place. The only way they could know about it yet be unable to correct it would be if there were a failure of the RCS (attitude control system) and that would be quickly fatal anyway.