Author Topic: Apollo LEM  (Read 23237 times)

Online the_other_Doug

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Re: Apollo LEM
« Reply #30 on: 08/06/2009 05:41 PM »
First, to Jim -- I have read in any number of books (particularly, IIRC, "Chariots for Apollo" by Pellegrino and Stoff) that the LM descent and ascent engines were never acceptance-fired, that they could not be successfully refurbished after firing.  Also, that the LM and CSM propellants, once loaded, set a "last date" by which the mission must be flown, after which the lines, gaskets, etc., in the propellant system had to be completely refurbished.  After having the hypergolics loaded, the spacecraft was only "good" on the pad for about a month before it would have to be taken down and the lines refurbished.

As for restarting engines, all of the Apollo spacecraft engines were capable of being restarted, but the APS was not cleared for restart until the program was in mid-stride.  Seems that the first-orbit rendezvous scheme that was used for Apollos 14-17 required an APS restart, and there was a fair amount of resistance to actually trying to restart it in flight.  It took a fair amount of work to convince the engineers that the APS could be used for a first-orbit TPI burn.

-the other Doug

Offline Jim

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Re: Apollo LEM
« Reply #31 on: 08/06/2009 05:59 PM »
First, to Jim -- I have read in any number of books (particularly, IIRC, "Chariots for Apollo" by Pellegrino and Stoff) that the LM descent and ascent engines were never acceptance-fired, that they could not be successfully refurbished after firing. 


2.  Also, that the LM and CSM propellants, once loaded, set a "last date" by which the mission must be flown, after which the lines, gaskets, etc., in the propellant system had to be completely refurbished.  After having the hypergolics loaded, the spacecraft was only "good" on the pad for about a month before it would have to be taken down and the lines refurbished.


1.  Show me an actual quote.  I have read the same books.  That is just not done. 

2.  SOP for hypergolic stages (Delta, Agena, etc)

Offline Proponent

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Re: Apollo LEM
« Reply #32 on: 08/07/2009 01:03 AM »
...  A single engined LM would basically have no abort mode in case of engine failure during descent.

An ascent engine failure carried much of the same risk.

But the ascent engine was particularly simple and reliable, which I believe is what Jim alluded to in his one-liner "Reliability" earlier in this thread. This simplicity was possible because, unlike the descent engine, the ascent engine did not need to be throttled.

Quote
The CSM SPS engine had to do that [restart] for TEI.

Still no reason not to minimize the risk of LM failure. And the SPS was almost two engines in one in that many of its components had back-ups.

Offline rsp1202

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Re: Apollo LEM
« Reply #33 on: 08/07/2009 01:32 AM »
Not to take this too far OT, but when Martin Caiden wrote "Marooned," the plot of which was triggered by the failure of the SPS engine to light -- despite all the best efforts of ground support, vendors and the astronauts to fix it -- Wally Schirra told him there was another method to get the thing to work that Caiden had overlooked, but he was going to keep it to himself so he could remain "one up" on the author. Never did find out what that was.

Offline Jorge

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Re: Apollo LEM
« Reply #34 on: 08/07/2009 01:46 AM »
...  A single engined LM would basically have no abort mode in case of engine failure during descent.

An ascent engine failure carried much of the same risk.

But the ascent engine was particularly simple and reliable, which I believe is what Jim alluded to in his one-liner "Reliability" earlier in this thread. This simplicity was possible because, unlike the descent engine, the ascent engine did not need to be throttled.

Or gimballed.
JRF

Online mike robel

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Re: Apollo LEM
« Reply #35 on: 08/07/2009 03:11 AM »
Not to take this too far OT, but when Martin Caiden wrote "Marooned," the plot of which was triggered by the failure of the SPS engine to light -- despite all the best efforts of ground support, vendors and the astronauts to fix it -- Wally Schirra told him there was another method to get the thing to work that Caiden had overlooked, but he was going to keep it to himself so he could remain "one up" on the author. Never did find out what that was.

Actually, I think that quote refers to the 1st edition version of Marooned which involved Mercury, Gemini, and Vostok.  I will have to dig the book out and check.  Although it might be that the quote was in the 2nd books forward, refering to the 1st book.

Offline rsp1202

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Re: Apollo LEM
« Reply #36 on: 08/07/2009 03:43 AM »
I hope you can find it and that I remembered it correctly. :) That would have to be where I saw it, but it's been years and yet it's stuck in my mind all this time. I also have to imagine that Schirra finally came clean, but have never heard the answer.

Online the_other_Doug

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Re: Apollo LEM
« Reply #37 on: 08/11/2009 01:32 AM »
Jim, as far as whether Apollo hypergol engines were fired prior to flight, I don't have the time to go hunting through my library at the moment.  I have run across this reference in more than one source, though.  If it's not true, then multiple people documenting the Apollo era have the fact wrong.

Do you (or Blackstar, or anyone else here) have any documentation of acceptance testing of Apollo flight DPS, APS or SPS engines?  That would also settle the question... all I have to go on are multiple reports in mainstream Apollo books of a "fact" that some seminal source may have gotten wrong.

It is true, though, that no LM DPS engine was ever fired *in flight* for its rated 12-plus-minute PDI lifetime prior to Apollo 11.  I'm sure many engines were fired through PDI profiles in ground testing, but in flight?  LM-5's DPS was the first.

-the other Doug

Online the_other_Doug

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Re: Apollo LEM
« Reply #38 on: 08/11/2009 01:43 AM »
...  A single engined LM would basically have no abort mode in case of engine failure during descent.

An ascent engine failure carried much of the same risk.

But the ascent engine was particularly simple and reliable, which I believe is what Jim alluded to in his one-liner "Reliability" earlier in this thread. This simplicity was possible because, unlike the descent engine, the ascent engine did not need to be throttled.

Or gimballed.

The LM APS was as simple and reliable as it could possibly be made.  It used pressure-fed propellants (no pumps), and there were a good half-dozen ways you could ignite the engine from the control panel, the PGNCS and/or the AGS.  And if all else failed, a piece of the ascent engine cover was removable and a special tool included in the LM manifest on each flight could be used to manually open the propellant feed lines and thus start the engine.

I also seem to recall there was an emergency procedure for using a PLSS battery to activate the APS and/or the guillotines that separated the ascent and descent stages at liftoff.  The idea was that, even if you drastically lost electrical power in the LM, you had a fighting chance of getting off the Moon and back into an orbit from which the CSM could rescue you.  (I realize you'd also have to have an operational RCS to maintain control during ascent, but there were a lot of ways to make the RCS fire, too...)

-the other Doug

Offline Jim

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Re: Apollo LEM
« Reply #39 on: 08/11/2009 02:13 AM »
Jim, as far as whether Apollo hypergol engines were fired prior to flight, I don't have the time to go hunting through my library at the moment.  I have run across this reference in more than one source, though.  If it's not true, then multiple people documenting the Apollo era have the fact wrong.

Do you (or Blackstar, or anyone else here) have any documentation of acceptance testing of Apollo flight DPS, APS or SPS engines?  That would also settle the question... all I have to go on are multiple reports in mainstream Apollo books of a "fact" that some seminal source may have gotten wrong.

It is true, though, that no LM DPS engine was ever fired *in flight* for its rated 12-plus-minute PDI lifetime prior to Apollo 11.  I'm sure many engines were fired through PDI profiles in ground testing, but in flight?  LM-5's DPS was the first.

-the other Doug

All engines are acceptance tested, especially manrated ones.

The SPS, DPS and APS weren't acceptance tested, but the engines were.

The LMDE

http://cbtsresidents.com/Spectrum/donharvey1.htm

http://pdf.aiaa.org/preview/CDReadyMJPC06_1178/PV2006_5220.pdf


Ascent engine

http://www.astronautix.com/details/fir17720.htm

SPS engine

http://books.google.com/books?id=y4jik85mL8EC&pg=PA157&lpg=PA157&dq=sps+engine+acceptance&source=bl&ots=JMIofOcJlm&sig=Bpbrz_tKqqZd5TvDza4RgXzPE_g&hl=en&ei=0NWAStqfKNK3twfE16DNCg&sa=X&oi=book_result&ct=result&resnum=7#v=onepage&q=sps%20engine%20acceptance&f=false
« Last Edit: 08/11/2009 02:25 AM by Jim »

Online the_other_Doug

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Re: Apollo LEM
« Reply #40 on: 08/11/2009 03:38 AM »
Thank you, Jim!  Indeed, indisputable references to qualification and acceptance tests run by actually firing the flight engines (under as benign conditions as possible, to be sure -- note the TRW man talking about how acceptance tests were run on the descent engines for periods of 30 seconds or less so as not to risk charring the ablative nozzle liners).

Again, many thanks.

-the other Doug

Offline YesRushGen

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Re: Apollo LEM
« Reply #41 on: 08/13/2009 03:21 PM »
Assuming an Apollo 13 type of incident, could the APS have been used for course correction burns?

Offline HarryM

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Re: Apollo LEM
« Reply #42 on: 08/13/2009 03:46 PM »
The ascent stage was only docked for a few hours to the CSM after return from lunar surface, nearly all of APS propellants would be gone and much of it's consumables, doesn't seem likely, LOC. An Apollo 13 incident after they had done the LOI burn but the LM had not yet seperated and begun powered descent would be more interesting. The DPS would have to do the TEI burn, and if that not enough, get rid of descent stage and also use the APS to do another burn and mid-course correction.


Online the_other_Doug

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Re: Apollo LEM
« Reply #43 on: 08/13/2009 07:45 PM »
A few of the scenarios that the flight controllers looked at during the Apollo 13 emergency included firing the DPS to fuel exhaustion and then staging and firing the APS to achieve a super-fast return.  This would have gotten the crew back so quickly (about 24 hours after the PC+2 burn) that the ascent stage's consumables would probably have gotten them home, but it would have required dumping the service module first, and no one wanted to see what would happen to the heat shield after 24 hours without the thermal protection of the SM.  Also, there would have been almost no delta-V left in the vehicle for midcourse corrections, and finally the flight controllers wouldn't have been able to top off the CM's batteries or have time to develop the entry checklist for 13's unusual configuration.

But using the APS *was* considered, as part of one of the several plans they could have followed.  The plan just had too many drawbacks.

-the other Doug

Offline YesRushGen

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Re: Apollo LEM
« Reply #44 on: 08/14/2009 02:50 PM »
Very interesting, Doug. Thanks for sharing!

- Kelly

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