The image I have is that if we turn off heating in a space vehicle, the cold will be immense. However, I started figuring in terms of energy levels of particles (which is the temperature) and realized that a cooling process is basically fast moving matter particles bouncing themselves slow by collisions with slower particles.

So, in space, if the heat (the quickies) can't bounce of the cold (the slowies) because there's vacuum outside of the space ship, so there's no matter at all, then the energy should be conserved withing the material domain of the vessel.

Am I wrong about it getting cold or am I misleading myself in the energy preservation reasoning?

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    $\begingroup$ In general, energy won't be conserved by a container in space. The shell of the container will radiate heat away constantly (albeit slowly); if the container is in Earth orbit (or near a star, in general) it will spend at least half its time in full sunlight, getting quite hot. $\endgroup$ Feb 10, 2016 at 20:24
  • $\begingroup$ @RussellBorogove Assuming that there's no star or any other radiation/energy source nearby, the temperature would drop, according to you. Could you please elaborate on why the energy/heat would dispers? $\endgroup$ Feb 10, 2016 at 20:28
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    $\begingroup$ @KonradViltersten You're neglecting heat loss due to radiation; that's electromagnetic waves generated by the motion of particles in the container's shell, not heat transferred to matter outside the container. $\endgroup$
    – DylanSp
    Feb 10, 2016 at 20:30
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    $\begingroup$ en.wikipedia.org/wiki/Thermal_radiation $\endgroup$ Feb 10, 2016 at 20:33
  • $\begingroup$ Related Does the ISS need more heating or more cooling? $\endgroup$ Feb 11, 2016 at 15:33

1 Answer 1


All objects in a vacuum will have a decreasing temperature, unless new heat is supplied. The reason for that is energy lost to thermal radiation, which is electromagnetic radiation carrying energy away. In fact, this is the same thing that allows the Sun to emit light even though surrounded by vacuum.

The magnitude of the radiated energy is proportional to the forth power of the absolute surface temperature. (The Stefan-Boltzmann law).

An object in space would eventually stabilize at a temperature where the energy radiated away is equal to the radiation absorbed, for example from sunlight. This temperature may as well be above liveable temperatures. For that reason, it is common to add extra surface area for radiation to a spacecraft, in order to keep the temperature within acceptable limits.

  • $\begingroup$ Worth noting, in Earth's distance to the Sun, for compact shaped spacecraft (sphere, box, tube) that equilibrium is generally above safe living temperatures and the container needs extra radiation surfaces - perpendicular to sunlight so their sunlight absorption area is small comparing to radiation area. $\endgroup$
    – SF.
    Feb 10, 2016 at 22:53
  • $\begingroup$ @SF. Edited in, hope you don't mind $\endgroup$ Feb 10, 2016 at 22:57
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    $\begingroup$ You could improve this by giving some examples of objects and the approximate stable temperatures they'd reach, especially for a spaceship. I'm sure this is well known for spacecraft and satellites. The lowest temperatures experienced during the night side pass, or something permanently in shadow would be also useful to add. $\endgroup$
    – Innovine
    Jul 10, 2019 at 17:06

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