lonewulf
Earth
Humanistic Cyborg
Posts: 244
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Post by lonewulf on Nov 20, 2005 0:09:59 GMT -4
Jeez; it's just 8 pounds. I lift more than that in my backpack EVERY DAY. And it's for emergency supplies. AND, it's in space/in moon gravity. What part of this is not getting through to you, Moon Man?
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Post by Obviousman on Nov 20, 2005 0:13:02 GMT -4
Obviousman, Thanks for the ALSJ link,my DSL chewed on it for a while but worth the wait! It does seem to confirm the numbers. Now, a bit of a question. In my favorite link, the -7 PLSS consumption/duration curve has two LIOH lines, one for "LiOH (min performance, nominal wt 3.22 lbs, no thermal soak)" and one for "LiOH(min performance, min wt 3.12 lbs, with thermal soak)" I'm not sure what the "thermal soak" and "min wt" variables affect. The two lines converge significantly on the "BTU/hr - EVA duration curve, so the difference diminishes over time in the EVA. Again, terrific link, gobs of neat stuff there... Dave This is just a guess, but I believe that the LiOH conversion process was ultimately exothermic. It might also be that the conversion is not as efficient at higher temperatures. So if the LiOH canisters were 'cold soaked' prior to use, it might give a longer useful life.
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Post by Moon Man on Nov 20, 2005 0:21:03 GMT -4
Jeez; it's just 8 pounds. I lift more than that in my backpack EVERY DAY. And it's for emergency supplies. AND, it's in space/in moon gravity. What part of this is not getting through to you, Moon Man? More handwaving and excuses from the ABer crowd.
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Post by LunarOrbit on Nov 20, 2005 0:30:14 GMT -4
More handwaving and excuses from the ABer crowd. And more willful ignorance from you. You were given an explanation for your made-up "problem" and you are unwilling to accept it... for what reason? An 8 pound canister ways only 1.3 pounds on the moon, and since it give the astronauts a safety margin it is worth the weight penalty. This is not a lame excuse, the safety of the astronauts was obviously important.
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Post by Obviousman on Nov 20, 2005 0:31:50 GMT -4
Jeez; it's just 8 pounds. I lift more than that in my backpack EVERY DAY. And it's for emergency supplies. AND, it's in space/in moon gravity. What part of this is not getting through to you, Moon Man? More handwaving and excuses from the ABer crowd. I've already answered that. Sufficient primary canisters to do the job. Interchangable secondary / PLSS canisters to still give LM life support and full duration EVAs if the primary system failed. YOU are mixing up the specs of the primary LM LiOH canisters and the LM secondary / PLSS canisters.
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Nov 20, 2005 0:39:32 GMT -4
I also wonder what the 14-hour rating is based on. Obviously CO2 production is much greater during periods of high physical exertion, and the astronauts were exerting themselves considerably during the EVAs. It could be that the 14-hour rating is based on an average rate of CO2 production; hence a canister's actually useful life during an EVA could be much less. If this is the case, then the 14-hour rated life could be a necessity and not just extra margin.
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Post by Moon Man on Nov 20, 2005 0:41:37 GMT -4
More handwaving and excuses from the ABer crowd. And more willful ignorance from you. You were given an explanation for your made-up "problem" and you are unwilling to accept it... for what reason? An 8 pound canister ways only 1.3 pounds on the moon, and since it give the astronauts a safety margin it is worth the weight penalty. This is not a lame excuse, the safety of the astronauts was obviously important. The canisters were brought to the moon from earth. If there is 8 extra needless pounds on earth then there is 8 extra needless pounds. There is no need for a 5 or so hour safety margin when it will never be used or needed. Because a fact is proven that does work in the ABers favour the ABers say; so what, it's only 8 pounds.
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Post by LunarOrbit on Nov 20, 2005 0:42:15 GMT -4
Weren't the Apollo spacesuits designed so that two astronauts could share one PLSS in an emergency? Could that explain the larger than necessary LiOH canisters?
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Nov 20, 2005 0:50:22 GMT -4
The canisters were brought to the moon from earth. If there is 8 extra needless pounds on earth then there is 8 extra needless pounds. There is no need for a 5 or so hour safety margin when it will never be used or needed. Because a fact is proven that does work in the ABers favour the ABers say; so what, it's only 8 pounds. We really don't know if the extra LiOH mass was needless or not because we really don't know if the method of rating the cannister lifetime is based on the same respiration rate as the PLSS oxygen supply. If the method of measurement isn't the same then you can't directly compare the numbers. You are jumping to conclusions withour having all the facts.
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Post by Obviousman on Nov 20, 2005 0:55:38 GMT -4
Weren't the Apollo spacesuits designed so that two astronauts could share one PLSS in an emergency? Could that explain the larger than necessary LiOH canisters? I don't think so. The buddy system shared the consumables, but took additional cooling water from the 'failed' PLSS. If they needed to go 'buddy', they would have halved the remaining consumables time.
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Post by scooter on Nov 20, 2005 1:04:17 GMT -4
Where are you getting this 8 extra pounds? The upgrade (to double the EVA time) was about .75 lbs for all the LiHO canisters. Where's the proof???
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Post by Obviousman on Nov 20, 2005 1:13:57 GMT -4
Okay - looking at the surface operations plan, the consumables allowed a minimum of 30 mins remaining upon completion of EVA. That's a 'max usage' rate, so they were being very conservative.
Here's the Type 7 PLSS consumables rate from the MOP for Apollo 15:
BATTERY
Battery rating: 23.1 A/hrs Pre-EVA checkout usage: -1.1 A/hrs Remaining: 22 A/hrs
EVA load: 2.6 Amps with additional 0.243 Amps for telemetry uncertainty.
Therefore 7 hours EVA with 30 minute reserve.
OXYGEN
Charge weight at 1420 PSIA: 1.804 lbs Penalties & residuals: - 0.354 lbs Usable O2: 1.450 lbs 30 minutes reserve: -0.102 lbs Available O2: 1.348 lbs
There is a forumula to calculate O2 usage - I'll post it if anyone wants. They also assumed a suit leak rate of 0.01 lbs/hr
FEEDWATER
Total loading: 11.90 lbs Losses: -1.04 lbs Usable feedwater: 10.86 lbs
10.86 lbs at 1038 BTU per pound heat of vapourisation provides 11 272 BTU of cooling capacity.
(forumla for cooling capacity usage rate)
EMU Heat Leak Rate:
EVA-1: -40 BTU/hr EVA-2: +230 BTU/hr EVA-3: +250 BTU/hr
LiOH
The LiOH consumption rate, although a function of the crewman's metabolic rate, has been found to be far in excess of that required for the planned 7 hour EVAs and is therefore not a constraint in traverse planning.
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Post by Moon Man on Nov 20, 2005 1:17:34 GMT -4
If an EVA went from 4 hours to 8 hours and the canister was only increased by .75 lbs to accomodate this doubling of time, how many hours did canister provide before the .75 lb increase..?
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Post by Obviousman on Nov 20, 2005 1:18:18 GMT -4
Weren't the Apollo spacesuits designed so that two astronauts could share one PLSS in an emergency? Could that explain the larger than necessary LiOH canisters? I don't think so. The buddy system shared the consumables, but took additional cooling water from the 'failed' PLSS. If they needed to go 'buddy', they would have halved the remaining consumables time. Oh, and they would have activated the OPS as well, if required.
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Post by Obviousman on Nov 20, 2005 1:42:50 GMT -4
Also, during the lunar surface operations, the following were brought aboard the LM / discarded:
EVA 1: Embark 1 x ECS LiOH canister Discard 1 x ECS LiOH canister
EVA 2: Embark 1 x ECS LiOH canister Discard 1 x ECS LiOH canister Discard 2 x PLSS LiOH canister
EVA 3: Discard 1 x ECS LiOH canister Discard 2 x PLSS LiOH canister
With 1 x ECS canister fitted and 1 x ECS spare aboard, and with 1 x PLSS canister fitted to each PLSS and 2 x ECS / PLSS canisters aboard for the secondary sytem at all times, I figure that was about the right amount that they took.
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