system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How can nuclear fission reactors in space lose their heat so they won’t melt themselves?
gpt
Usually they’ll have radiators, which are not like the radiators in your house. On Earth it’s a lot more straightforward to get rid of heat. You just push it somewhere else. There’s stuff everywhere, so you can give that heat to other stuff. That’s conduction. 

In space there isn’t a lot of stuff, so you usually have to get rid of it through radiation instead of conduction. Anything with any temperature (so everything) gives off some light. Most of this is infrared, so we can’t actually see it, but everything is constantly shooting out little bits of light. Some materials are better at giving off infrared than others and so usually you’ll just make a big surface covered in one of those materials. You’ll basically just transfer heat over to the radiator using normal conduction, and then let the radiator shoot it off into space as infrared.