system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5: besides safety concerns, what other reasons are there for not using nuclear powered engines in rockets for long term space travel?since they are used in submarines?
gpt
Nuclear power *is* used in space travel. Not in the same form as sub reactors, though.

Nuclear reactors are big and heavy. This is a problem for space travel. They also produce a lot of heat, and if that heat is not shed quickly, the reactor is very inefficient. That means a lot more weight in radiators.

We currently use RTG's, very simplistic nuclear power banks that generate very little power, in some space travel, but they are not ideal when sunlight is so conveniently available.