Does a space capsule need to be heated, or cooled?

December 3, 2011 11:52 PM

In a 'typical' space capsule - Apollo, etc. - how do they maintain a constant temperature for the astronauts? Do they have to heat the capsule, to replace heat radiated out to space, or do they have to refrigerate it, against the incoming solar radiation?

And who gets to decide where to set the thermostat - the mission commander? Does the crew start changing the settings behind each other's back, because each person is 'too cold' or 'too hot', like in many homes?

posted by woodblock100 to technology (10 answers total)

It's harder to radiate heat into space -- a vacuum is a very effective insulator, and things like computers and humans are good at generating heat, so spacecraft generally need 'air conditioning' to stay cool.
posted by AzraelBrown at 12:00 AM on December 4, 2011

The Apollos got cold when they lost power; they required heat. On the Apollo 13 (the movie) Anniversary Edition commentary, Jim Lovell talks a little about this; he says if you stay very still in zero gravity, your body heat warms the air molecules around you and creates a little pocket so you stay warm(er), until someone comes in and moves your air molecules. (He talks about this over a scene where Tom Hanks is floating still with his arms cross/wrapped around himself and appears to be sleeping (and doing what Lovell is talking about, though you wouldn't know it without the commentary track), when the ship is cold (well after the accident) and they haven't done the final burn yet or jettisoned the LEM.)

This article talks about why Skylab got hot and Apollo 13 got cold when each suffered system failures.
posted by Eyebrows McGee at 12:15 AM on December 4, 2011 [5 favorites]

...if you stay very still in zero gravity, your body heat warms the air molecules around you and creates a little pocket so you stay warm(er), until someone comes in and moves your air molecules.

This happens in regular gravity on earth, too. It's why wind chills you, removing the warm air from your body and replacing it with cooler ambient air.
posted by knave at 1:10 AM on December 4, 2011 [2 favorites]

This happens in regular gravity on earth, too.

The effect should be more pronounced in zero g, because there is no natural convection (hot air doesn't rise away).
posted by wilko at 2:37 AM on December 4, 2011 [1 favorite]

Energy usage in every spacecraft except possibly the ISS is very heavily regulated. Changing a thermostat would require radioing down to Houston and having a room full of engineers run calculations on energy consumption.

Also, those things have a lot of insulation.
posted by gjc at 6:00 AM on December 4, 2011

And who gets to decide where to set the thermostat - the mission commander? Does the crew start changing the settings behind each other's back, because each person is 'too cold' or 'too hot', like in many homes?

Skip to 5:20 in of this video for footage of Apollo 12 Lunar Module Pilot talking about the environment of LM while they were on the moon. He does say that they could adjust the temperature in the cabin. The moonwalkers also wore special long john style underwear, which was laced with tubes to carry water to help keep them cool while on the lunar surface.

Keep in mind that by the time the astronauts were in space, they had been training at least months (six months for Apollo 11), sometimes years (Apollo 9's crew trained for three years), as a crew for the mission. They knew each other inside and out and that probably included who got too hot or cold, so they made adjustments among themselves. After all, when you're locked inside 215 feet of cubic space with two other people for 3 or 4 days at a time, you don't want to piss anyone off. Plus, these guys were military pilots, fully aware they were getting a rare chance to do something incredible. Their focus was the mission and minor stuff didn't phase them as much.

I've also seen photos of Apollo astronauts with an umbilical cord hooked up to their casual wear while in the cabin, while in the Command Module. Start at the 45 second mark in this music video, which contains footage from the Apollo 9 mission. Notice that the guy in the lower frame has some sort of cord feeding directly into his suit, over his right breast. That's probably a line feeding cool air directly to him, but that's just a guess.

Footage of Skylab, Mir, Shuttle and ISS astronauts have shown them in everything from just shorts with no top, to long sleeve pants and shirts. I'm guessing that the temperature on the space stations was set to a specific number the inhabitants were free to dress how they wanted to to stay comfortable.

The other thing to keep in mind is that putting the ship in some sort of roll was common practice, just so that one side wasn't always facing the 250+ heat of the sun, while the other soaked in the -250 cold of the shadows. The spinning was called "barbeque mode" for obvious reasons. Not sure how the ISS spins or moves.

Energy usage in every spacecraft except possibly the ISS is very heavily regulated. Changing a thermostat would require radioing down to Houston and having a room full of engineers run calculations on energy consumption.

I think it was more along the lines of mission control monitoring everything and if they saw that environment controls were sucking too much power they'd have the astronauts make a change.
posted by Brandon Blatcher at 7:02 AM on December 4, 2011

The Apollo capsules enroute to the moon used the "barbeque roll maneuver", properly known as "passive thermal control" in which the spacecraft slowly rolled around its axis to evenly expose the entire surface to both the heat of the solar infrared and the coldness of deep space.
posted by autopilot at 7:51 AM on December 4, 2011

The ISS doesn't need to roll very much, if at all. First, it's orbiting, so it's in shadow part of the time, and second, it's partially reliant on solar power.
posted by Cool Papa Bell at 10:12 AM on December 4, 2011

Well, the ISS is more properly constantly changing its solar orientation, because its orbital stance is in relation to Earth. More on the myriad ISS thermal control systems.

Changing a thermostat would require radioing down to Houston and having a room full of engineers run calculations on energy consumption.

I wouldn't be so sure. The crew on board have a lot of direct control interfaces -- while the actual systems tend to be various RTOS OEM thingies, they almost always are actually manipulated by custom software on a Windows laptop. I have heard of daytime/nighttime schedules and the like, as well as rigged fans and so on to control temp and airflow in individual modules, especially the ones used for sleep.
posted by dhartung at 10:55 AM on December 4, 2011

Interestingly enough, the craft will also typically require complex heating systems to ensure that the hydrazine that powers/fuels the APUs is kept warm throughout the mission. (Or it will freeze, expand, and burst the fuel line. This would be a Bad Thing.) So for the fuel lines running throughout the vehicle (the space shuttle, in this case), they need to be heated.

A failed hybrid driver kept a heater string down and out for the first launch attempt for STS-134, Endeavour's final launch. The backup string worked just fine, but Launch Commit Criteria require both heater strings to be fully operational before launch—they won't launch on a backup, essentially. This took Endeavour out of the count for a few weeks while they troubleshooted in the aft compartment (which takes on a completely different orientation when the shuttle is on the pad, compared to how it is when they're working on it in the Orbiter Processing Facility: horizontal. Not to mention that you can't touch anything. They have to lay down panels so they can climb around and be careful in the full 3D space around them since lines and cables are running all around them) and replaced the Aft Load Control Assembly that contained the Hybrid Driver. Since this is a very complicated fix, and since the ALCA handles much more than just heaters, they had to recertify for flight all of the other elements of space flight the ALCA touches, AND the heater strings.

Worse, because the failed driver indicated a short circuit somewhere further downstream, the technicians were concerned that they could install a new ALCA box, turn it on, and have the short occur again. This would be incredibly bad. So they performed hi-pot tests to see if they could identify the location of the short.

The investigation quickly turned to one of the thermostats itself, since it had triggered a voltage spike back in its certification tests almost a year earlier, for just a moment. The spike didn't affect the test, but it was soon determined that it occurred while a technician was attempting to activate the thermo with a metal heat gun. The heat gun made brief contact with the metal head of the thermostat, which had a slight exposed conductor right at the connector as well. They couldn't definitively say that it was the thermo, since it was still possible to positively test the removed thermo, but they figured that this was the most likely cause, and since they had replaced and recertified everything along the failure chain, they predicted a very low chance of the problem reoccurring.

Or, why I made two trips to Florida two months apart.

But hey, I got some great photos and gave the fiancée a great proposal story.

Spaceflight is HARD.
posted by disillusioned at 11:54 AM on December 4, 2011 [3 favorites]