Author Topic: Retention of the Ascent Stage through Trans Earth Injection  (Read 1278 times)

Offline Jim Davis

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Around the turn of the century there was a discussion on the sci.space.history forum of USENET (fun times) about the use of the ascent stage RCS as a backup for the CSM RCS during TEI and beyond. Briefly, I remember that in case of a failure in the CSM RCS, the LM ascent stage would remain docked with the CSM and use its RCS to control the stack during TEI and the return to earth.

This struck me as unlikely for two reasons. The obvious one was the impact such a scheme would have on both the CSM and LM designs when weight was all important. If CSM RCS failure was feared wouldn't added redundancy be a better way to deal with the issue? Secondly, during the actual lunar missions the LM ascent stage was jettisoned shortly after rendezvous with the CSM, sometimes a considerable time before TEI. Wouldn't the ascent stage be retained as long as possible if it was seen to be so valuable as a backup? Indeed, why jettison it at all until right before reentry if the margins were available to retain it?

Yet several posters claim that this was indeed an option and claimed to have appropriate documentation.

Has anyone here heard of this scenario?

If it indeed was a real option, can you detail the tradeoffs involved?

This always seemed incredible to me.

Offline indy91

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I found one reference to this. From the Apollo 11 Mission Rules (https://www.hq.nasa.gov/alsj/a11/A11MissRules.pdf), Section CSM SM-RCS:

Quote
17-4 Lunar Orbit

... Loss of two quads is cause for terminating lunar orbit or lunar stay phases, and is also cause for performing TEI with the LM DPS or retaining the LM ascent stage through TEI for attitude control.

So yes, apparently they had a plan to keep the ascent stage for TEI for certain contingencies.

« Last Edit: 06/25/2018 07:33 PM by indy91 »

Offline Patchouli

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Interesting I wonder if there was a scenario to keep the ascent stage in case of loss of pressurization of the CM?

Offline Proponent

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Was it possible to charge the LM's batteries with the SM's fuel cells?  If not, I suspect the ascent stage's viability was too short for it to have been of much use as a back-up pressurized habitat.

Offline RIB

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So what was the dry weight of the Apollo 11 LM? I wonder if the added weight would have cut very deeply into the SPS propellant margin? Oh well, if necessary, they could have always dumped the rocks..... :D :D :D :D :D

Offline Proponent

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Try googling "Apollo by the Numbers" to get the LM's mass.

Offline Michel Van

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according NSSDCA/COSPAR ID: 1969-059C

Ascent stage mass is 4821 kg
The dry mass of the ascent stage was 2445 kg and it held 2376 kg of propellant.

According Apollo by numbers

Had the LM Ascent stage  2376 to 2460 kg  on fuel 
remaining fuel is around 191 to 112 kg
i get that right they could transfers that fuel into RCS system (Apollo 16)
now that give around 2595 kg LM Ascent stage docked on CSM in lunar orbit

They have get a delta v of 928,51 meter/sec for TEI
The Data say that CSM mass at standart TEI is around 16737 kg.
after TEI the CSM mass is around 12153 kg.

sadly Apollo by numbers  give no info about remaining fuel on CSM after TEI.
so i don't know if a CSM+LM ascent could manage a TEI...

Offline TripleSeven

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Was it possible to charge the LM's batteries with the SM's fuel cells?  If not, I suspect the ascent stage's viability was too short for it to have been of much use as a back-up pressurized habitat.

I am sure it was that was how the batteries stayed "topped off"

Offline Proponent

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Next question:  what about cooling?  Was the ascent stage water cooled?

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