Heat radiation in a vacuum is also an important aspect of space travel. If heat could not radiate in a vacuum, we would not be able to dump excess heat from space craft and, at some point, the combination of electric devices operating within the pressure vessel and human heat output would eventually roast the people inside. We need heat to radiate outwards, and, from my understanding, it’s actually a somewhat difficult problem to solve in a vacuum. We take air and evaporative cooling for granted sometimes when on Earth and in space, where air cooling isn’t going to happen, you have to practice other methods of heat transfer.