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Post by PeterB on Jul 22, 2010 5:49:57 GMT -4
Were these systems outside the LM's pressure vessel? That would make it impossible to dump the heat back inside.
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Post by trebor on Jul 22, 2010 5:51:18 GMT -4
Why couldn't the waste heat from the LM electronics have been dumped into the cabin to keep the astronauts warm instead of being dumped overboard by the sublimator, consuming precious water while the astronauts froze? I'm sure if you were designing the system you could build it in a way where this would be possible.
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Post by kallewirsch on Jul 22, 2010 5:57:37 GMT -4
Just guessing:
Because nobody ever tried it (or even thought of it) and they didn't want to make matters worse as long as not absolutely needed.
What I always wondered: When it became pretty cold for sleeping, why didn't they use their space suits as some sort of sleeping bag to help keep the body warmed air near the body when turning during sleep.
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Post by Jason Thompson on Jul 22, 2010 7:57:37 GMT -4
They considered the spacesuits, but decided against them. Firstly it would make an already uncomfortable situation more cramped, and secondly, with no airflow inside it, the uncooled spacesuit would have caused them to perspire, making their clothes wet (as well as increasing their need for drinking water). They decided it was better to be cold and dry than to be in damp clothing.
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Post by randombloke on Jul 22, 2010 9:42:33 GMT -4
Plus weren't there only two of the full Lunar EVA suits?
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Post by echnaton on Jul 22, 2010 22:14:21 GMT -4
Were these systems outside the LM's pressure vessel? That would make it impossible to dump the heat back inside. The electronics that needed cooling were attached to a cold plate which was in tern chilled by the circulating coolant. There may have been no route to bring the heat back into the LM but being outside does not seem to be the reason.
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Post by ka9q on Jul 23, 2010 3:20:39 GMT -4
Were these systems outside the LM's pressure vessel? That would make it impossible to dump the heat back inside. I've studied the manuals for the heat transport section of the LM's environmental control system. There are two glycol/water coolant (essentially ordinary antifreeze, like you have in your car) loops, primary and secondary. The secondary loop was only used if the primary failed, so setting it aside, the primary coolant loop was as follows: Pumps; check valves; electronic equipment cold plate & suit gas heat exchanger (in parallel; the suit gas exchanger flow could be adjusted for comfort); liquid cooling garment heat exchanger; aft equipment bay cold plates; suit gas heater (also bypassable for temperature control); primary sublimator; ascent and descent battery cold rails; and back to the pumps. Obviously the order of these nodes is important, as each one will be warmer than the previous one until the coolant reaches the sublimator where it reaches its lowest temperature in the system. That the batteries immediately followed the sublimator says that the engineers wanted them colder than everything else. The relevant part for Apollo 13 is the suit gas heater. It comes right before the sublimator, so I don't see why it wasn't possible to simply shut off the sublimator water supply and dump all of the heat generated by every LM system right into the cabin to warm the crew. Running the sublimator (and consuming water) should have been necessary only if the crew became overheated (which didn't happen) or some subsystem (the batteries, perhaps?) had to be kept even colder than the crew. So I still don't understand this. My reference is the Apollo Operations Handbook, Lunar module LM 10 and subsequent, Volume 1, subsystems data. Since Aquarius was LM7, it's entirely possible that its heat transport system was not as documented here. Maybe the later LMs were reworked specifically because of Apollo 13's experience to permit warming the crew with waste heat without running the sublimator? Maybe the suit gas heater didn't even exist on LM7? I haven't yet found an earlier version of this reference that covers LM7. Perhaps this was covered by the recommendations of the Apollo 13 review board. That's another reference to check.
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Post by kallewirsch on Jul 23, 2010 8:06:42 GMT -4
so I don't see why it wasn't possible to simply shut off the sublimator water supply and dump all of the heat generated by every LM system right into the cabin to warm the crew. Hmm. Which brings up a question on my own: Which of the LM systems were still running and produced how much heat?
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Post by ka9q on Jul 23, 2010 13:08:36 GMT -4
I don't know how much power was drawn by each LM system still running on Aquarius, but the total consumption in the powered-down state is given in the histories as 12-14 amps. If the batteries were at 29 volts, that's 348-406 watts.
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Post by ka9q on Jul 23, 2010 13:16:59 GMT -4
I brought this up on another forum, and Frank O'Brien responded with an explanation that essentially boiled down to that secondary heat exchanger (the one intended to warm the suit gas circuit) just wasn't very effective at transferring heat.
If he's right, then it meant that the coolant would have had to get unacceptably warm before significant heat could have been transferred to the cabin and/or suit gas circuits to warm the astronauts.
Which, to me, raises the question of why even bother to have that second heat exchanger there. Under normal operating conditions there'd be a lot more waste heat from the electronics. The cabin would be at a comfortable temperature, and the heat transport section would only have to remove the astronauts' metabolic heat, not warm them up.
One way to make a heat exchanger more efficient is to change the fluid from air to water. The LM did provide cooled water for (two) astronauts' liquid cooling garments, which I take as tacit evidence that the heat exchanger used to cool the suit gas circuit (and cabin atmosphere) wasn't very effective either. The CSM cooled the astronauts only by cooling their suit gas, so it must have had a more efficient or effective gas/coolant heat exchanger.
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