During Apollo 13, why did the spacecraft get so cold, when it didn't have power?

[szputnyik]

I've always read that during space travel, it is needed to cool the spacecraft, not heat it, because although space is cold, the near-vacuum is a very good insulator and the humans and electronics inside give off plenty of heat, that needs to be radiated into space as efficiently as possible, otherwise the spacecraft could overheat.

However, during Apollo 13, when, after the explosion, the crew was trying to stay alive in the underpowered LM, the temperature almost went sub-zero. Wikipedia says that happened because there was so little power left. Shouldn't the LM have overheated instead, when the crew's bodies were giving off all that heat, and there was no power to radiate it out into space?

[Ralathon]

When they designed the LEM they took the heat generation into account. That's one of the reasons the LEM has all those flat surfaces and angles: To passively radiate the heat from the computer and astronauts.

During Apollo 13 they had to shut down all the fancy tech, so they removed a lot of heat generation. But they couldn't adjust the shape and materials of the spacecraft, so they kept radiating heat at the same rate. This means the ship got colder.

[lajoswinkler]

When you think of the actual numbers involved, they didn't cool down a lot. If their operating temperature was 20°C, and they went to zero, that's 20 degrees of difference. They could've gone to a lot lower values.

Zero is quite warm, actually.

[jwenting]

mind that some of the biggest heat generators on board were still there, they were the 3 carbon based units, otherwise called astronauts.

[Monkeh]

Vacuum an insulator? That sounds very wrong. It all depends on where the sun is. If you're in the suns path with no atmosphere and no magnetic field to help it would get very hot very quickly. If you're in shadow it will get very cold very fast. This is why space vehicles slowly rotate. Think chicken on a spit slowly barbequeing. Yummy.

[Technical Ben]

The Vacuum is an insulator against convection, not radiation. So it depends on the radiative factors, such as sun exposure (or the absence of) and the radiators of the craft it's self.

[sjwt]

When you think of the actual numbers involved, they didn't cool down a lot. If their operating temperature was 20°C, and they went to zero, that's 20 degrees of difference. They could've gone to a lot lower values.

Zero is quite warm, actually.

It all depends on what you are dressed for,

If you are dressed for 20, going to 0 is not going to be fun.

[lajoswinkler]

Vacuum an insulator? That sounds very wrong. It all depends on where the sun is. If you're in the suns path with no atmosphere and no magnetic field to help it would get very hot very quickly. If you're in shadow it will get very cold very fast. This is why space vehicles slowly rotate. Think chicken on a spit slowly barbequeing. Yummy.

Yes, vacuum is the best insulator. The only heat transfer from a body into the space is radiative, and it will stop at background radiation temperature. In fact it never stops, it's just reaching the equilibrium.

http://en.wikipedia.org/wiki/List_of_thermal_conductivities

It all depends on what you are dressed for,

If you are dressed for 20, going to 0 is not going to be fun.

And you know what that means...

[potatomaster]

Vacuum is the best insulator, that's why thermos' have a vacuum between the container and outer skin.

[Godot]

mind that some of the biggest heat generators on board were still there, they were the 3 carbon based units, otherwise called astronauts.

Which, of course were taking into account, when the engineers calculated the heat dissipation capacity needed for the trip.

Without them as heat generators, the interior of the capsule would surely have gotten much colder than it did

[MennoLente]

Wouldn't it be possible to regulate temperature by orienting the LEM towards the sun to cool, and the side to warm? Of course the leak and limited RCS would mess that plan up, but in theory?

[check]

Did they ever put on any part of their EVA suits to keep warm? Granted they're bulky and probably a pain to get in and out of, but surely it'd be a good way to keep from freezing.

[Kryten]

Wouldn't it be possible to regulate temperature by orienting the LEM towards the sun to cool, and the side to warm? Of course the leak and limited RCS would mess that plan up, but in theory?

Looking at the shape of the LM cabin, there simply isn't a lot of difference between the side-on area and that from the top, so I'm not sure that'd have helped.

[Nibb31]

Did they ever put on any part of their EVA suits to keep warm? Granted they're bulky and probably a pain to get in and out of, but surely it'd be a good way to keep from freezing.

That's a damn good question. They had 3 suits on board (2 were for lunar and contingency EVAs, the third was a lighter one for the CMP in case a contingency EVA required to depress the CM). There was a thread about this on NSF. The answer on that thread seems to be that they would have been too warm in the suits without hooking them up to the recirculation fans (for which they had no power to spare) and the sweat, while being dehydrated from water rationing and being in a cold atmosphere, would have made things worse.

Edited October 17, 2013 by Nibb31

[Brotoro]

Did they ever put on any part of their EVA suits to keep warm? Granted they're bulky and probably a pain to get in and out of, but surely it'd be a good way to keep from freezing.

As I recall, the two who had moon-walking boots wore those to keep their feet warm.