Author Topic: Apollo LEM  (Read 56065 times)

Offline Uncle Jean

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Apollo LEM
« on: 08/02/2009 01:33 pm »
Hi all,

I think all the components of Saturn V were wonderful but particularly the Apollo lunar module, which was really impressive to me.  Small, light but it was the reflect of much creativity.  And as we know, it never failed.

Some technical information can be found here, among others:
http://www.cs.indiana.edu/sudoc/image_30000061709352/30000061709352/pdf/techdata.htm#lunar

This link may not be new but too late to wonder now... :)

How do you see it ?

Uncle Jean

Offline dairwin

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Re: Apollo LEM
« Reply #1 on: 08/04/2009 06:49 pm »
The LEM, like so much of the program, was pared down to the essential elements of its mission.  Clearly defined objectives, well considered variables, contingency cases and no fuss.  It repeatedly achieved its mission.

Offline the_other_Doug

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Re: Apollo LEM
« Reply #2 on: 08/04/2009 08:01 pm »
Well, yeah -- the LM as a whole never failed during a manned mission.  There were scores of little failures and glitches throughout the program, though.  Some of them (like the window failure in LM-1 during testing, when the Commander's front window failed in a vacuum chamber and rapidly depressurized the cabin) would have been disastrous if they had happened during a manned mission.  (LM-1 flew with aluminum sheets instead of windows because of that failure, which had not been resolved by the time of LM-1's Apollo 5 flight.)

Yes, the LM was a remarkable little spacecraft.  It was also likely one of the riskiest spacecraft ever flown by men -- margins were pared down so fine that many of the mission phases (especially lunar lift-off) had single-point-failure scenarios that could result in LOCV.  And more than once, LM system failures brought some crews into backup modes that indeed left them intolerant of any further failures in that specific system.  But, on the whole, the LM performed amazingly well.

-the other Doug
-Doug  (With my shield, not yet upon it)

Offline Uncle Jean

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Re: Apollo LEM
« Reply #3 on: 08/05/2009 09:52 am »
Thanks for your comments, guys.

The fact is the more I read technical information about the LEM, the more I like it.  :)

Regards,
Uncle Jean

Offline SnowBars

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Re: Apollo LEM
« Reply #4 on: 08/05/2009 04:05 pm »
It was also likely one of the riskiest spacecraft ever flown by men -- margins were pared down so fine that many of the mission phases (especially lunar lift-off) had single-point-failure scenarios that could result in LOCV.

Thank you for detailed information.

Every time I saw lift-off footage I was puzzled where those exhaust gazes escape to? I checked your references again and I don’t see enough space between ascending and descending modules, and top of descending module looks flat (with descending engine below). Do you know if it used some sort of solid fuel engines for the first few seconds of lift-off?

Offline Analyst

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Re: Apollo LEM
« Reply #5 on: 08/05/2009 04:17 pm »
It didn't. Just one engine plus 16xRCS.

Analyst

Offline Jim

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Re: Apollo LEM
« Reply #6 on: 08/05/2009 04:20 pm »

Every time I saw lift-off footage I was puzzled where those exhaust gazes escape to? I checked your references again and I don’t see enough space between ascending and descending modules, and top of descending module looks flat (with descending engine below). Do you know if it used some sort of solid fuel engines for the first few seconds of lift-off?


No solid motors.  The ascent engine intruded into the crew cabin so that the nozzle was flush with the top of descent stage.  The propellants of the ascent stage burn with a translucent flame.

http://www.hq.nasa.gov/office/pao/History/SP-4205/ch6-3.html

In the 3rd figure, one astronaut is sitting on the ascent engine cover
« Last Edit: 08/05/2009 04:23 pm by Jim »

Offline SnowBars

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Re: Apollo LEM
« Reply #7 on: 08/05/2009 05:07 pm »
As far as I understand RCS were used only for orientation.


The ascent engine intruded into the crew cabin so that the nozzle was flush with the top of descent stage.  The propellants of the ascent stage burn with a translucent flame.

I don't have any issues with flame color. I'm trying to understand where those gazes escape. I’m not rocket scientist but it seems to me that ascending engine should explode if nozzle was flush with the top of descent stage. 

Offline Analyst

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Re: Apollo LEM
« Reply #8 on: 08/05/2009 05:35 pm »
As far as I understand RCS were used only for orientation.

Correct.

Analyst

Offline Jim

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Re: Apollo LEM
« Reply #9 on: 08/05/2009 06:26 pm »
I don't have any issues with flame color. I'm trying to understand where those gazes escape. I’m not rocket scientist but it seems to me that ascending engine should explode if nozzle was flush with the top of descent stage. 

http://www.hq.nasa.gov/office/pao/History/SP-4205/ch6-2.html

Look at the 3rd pic.  The hole in the middle is where the descent engine went, but it did not fill the whole volume.

Offline Danderman

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Re: Apollo LEM
« Reply #10 on: 08/05/2009 06:30 pm »
Was there ever a serious thought to testing just the ascent stage of the LM? Given its loaded weight of 10,000 lb, a partially fueled ascent stage may have been orbited by a Titan II, and certainly by a Saturn I. I can't think of a technical reason why the ascent stage could not be flown as a separate, early test, and given that the LM was in the critical path for Apollo, and it was plagued by delays, I can't see why this would not have been considered.

Offline wannamoonbase

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Re: Apollo LEM
« Reply #11 on: 08/05/2009 06:40 pm »
Even from a very early age I always thought the LEM was a great looking machine.  But then again as an engineer I see past alot of the aesthetics.  I never understand when people refer to it as ugly or a spider. 

It's a really excellent example of a vehicle taking the shape required by it's mission.

I think one of my favorite aspects is how they combined the 2 fuel and 2 oxidizer tanks into 1 of each and then off set them from the axis of the vehicle by the ratio of lengths vs weights to keep it balanced during the engine burns.  A beautiful insight and solution.
Wildly optimistic prediction, Superheavy recovery on IFT-4 or IFT-5

Offline Jim

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Re: Apollo LEM
« Reply #12 on: 08/05/2009 06:53 pm »
Was there ever a serious thought to testing just the ascent stage of the LM? Given its loaded weight of 10,000 lb, a partially fueled ascent stage may have been orbited by a Titan II, and certainly by a Saturn I. I can't think of a technical reason why the ascent stage could not be flown as a separate, early test, and given that the LM was in the critical path for Apollo, and it was plagued by delays, I can't see why this would not have been considered.

The additional integration effort and hardware development would have added more work.

Also:

A.  The loads of another launch vehicle may be incompatible
B.  Partially fill tanks are big deal for launch integration

Offline SnowBars

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Re: Apollo LEM
« Reply #13 on: 08/05/2009 07:47 pm »

http://www.hq.nasa.gov/office/pao/History/SP-4205/ch6-2.html

Look at the 3rd pic.  The hole in the middle is where the descent engine went, but it did not fill the whole volume.

This sounds like the only possible scenario. I saw some sort of cover on top of descent engine. Did it have a hole in the middle?
http://history.nasa.gov/alsj/a11/a11LM5structures.pdf (page 4)

I have another, probably stupid, question. Why not to use just one engine? Both engines used same fuel and descent engine was 3x more powerful, so it could lift-off just fine. Plus, they could throttle it. It would save development costs and lunar module mass.


Offline Jorge

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Re: Apollo LEM
« Reply #14 on: 08/05/2009 08:07 pm »

http://www.hq.nasa.gov/office/pao/History/SP-4205/ch6-2.html

Look at the 3rd pic.  The hole in the middle is where the descent engine went, but it did not fill the whole volume.

This sounds like the only possible scenario. I saw some sort of cover on top of descent engine. Did it have a hole in the middle?
http://history.nasa.gov/alsj/a11/a11LM5structures.pdf (page 4)

I have another, probably stupid, question. Why not to use just one engine? Both engines used same fuel and descent engine was 3x more powerful, so it could lift-off just fine. Plus, they could throttle it. It would save development costs and lunar module mass.



Descent engine could get damaged on landing and not be capable of liftoff.

This is not a hypothetical - Apollo 15 crew would have been stranded on the moon if the LM only had one engine:

http://forum.nasaspaceflight.com/index.php?topic=18095.msg451566#msg451566
JRF

Offline SnowBars

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Re: Apollo LEM
« Reply #15 on: 08/05/2009 08:16 pm »

I think one of my favorite aspects is how they combined the 2 fuel and 2 oxidizer tanks into 1 of each and then off set them from the axis of the vehicle by the ratio of lengths vs weights to keep it balanced during the engine burns.  A beautiful insight and solution.

I'm not sure what you mean. Each stage had its own tanks. http://upload.wikimedia.org/wikipedia/commons/e/e0/LEM-linedrawing.png

IMHO they put those tanks too far from the center of gravity. As far as I know, those engines use fuel and oxidizer in different proportion so it makes hard to balance the center of gravity. Ascent module had only one fixed engine and very small RCT for corrections.
« Last Edit: 08/05/2009 08:24 pm by SnowBars »

Offline SnowBars

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Re: Apollo LEM
« Reply #16 on: 08/05/2009 08:23 pm »

Descent engine could get damaged on landing and not be capable of liftoff.


This wouldn't happen with single engine version because this engine would stay very high in ascent stage. It could break but same could happen with ascent engine in Apollo as well.

Offline Jim

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Re: Apollo LEM
« Reply #17 on: 08/05/2009 08:30 pm »

I have another, probably stupid, question. Why not to use just one engine? Both engines used same fuel and descent engine was 3x more powerful, so it could lift-off just fine. Plus, they could throttle it. It would save development costs and lunar module mass.


Reliability

Offline Jim

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Re: Apollo LEM
« Reply #18 on: 08/05/2009 08:34 pm »

I think one of my favorite aspects is how they combined the 2 fuel and 2 oxidizer tanks into 1 of each and then off set them from the axis of the vehicle by the ratio of lengths vs weights to keep it balanced during the engine burns.  A beautiful insight and solution.

1.  I'm not sure what you mean. Each stage had its own tanks. http://upload.wikimedia.org/wikipedia/commons/e/e0/LEM-linedrawing.png

2.  IMHO they put those tanks too far from the center of gravity.

3. As far as I know, those engines use fuel and oxidizer in different proportion so it makes hard to balance the center of gravity. Ascent module had only one fixed engine and very small RCT for corrections.


1. The original LM  concept had 4 tanks in the ascent stage like descent stage to balance the propellant.

2.   Based on what data? 

3.  The fuel and oxidizer had different densities, which necessitated the offset tanks
« Last Edit: 08/05/2009 08:37 pm by Jim »

Offline Jim

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Re: Apollo LEM
« Reply #19 on: 08/05/2009 08:36 pm »

Descent engine could get damaged on landing and not be capable of liftoff.


This wouldn't happen with single engine version because this engine would stay very high in ascent stage. It could break but same could happen with ascent engine in Apollo as well.

No, a descent engine could not be that high in the vehicle like the ascent engine.  There would be too much heating from the plume

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