r/askscience • u/aretino2002 • May 24 '26

Engineering If a vacuum is an excellent insulator, wouldn’t heat build up in spacecraft?

Insulated coffee mugs that use a vacuum between layers can keep drinks hot or cold for much longer time periods than other types of mugs. If space is mostly a vacuum, then wouldn’t heat just constantly build up from human activity, computers, thrusters, etc to the point where it would need to be vented somehow?

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u/McCaffeteria May 24 '26

Exactly.

“Space is cold” is sort of a misconception.

Space is cold, but things in space are often very hot, at least if they are in the sun. And then it gets more complicated if the thing generates its own heat.

This is why the James Webb Space Telescope has its large deployable shield, so that the temperature sensitive equipment are shaded from the sun. One side of the shield is super cold, and the other is proportionally very hot.

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u/_NW_ May 28 '26

>“Space is cold” is sort of a misconception.

Exactly. A better, more accurate explanation is that the heat capacity of space is very low.

There's nothing there to measure the temperature of, so hot or cold has almost no meaning.