[rsynnott]

> Nuclear rockets don't have the thrust ratio necessary for take off, so presumably they'd be assembled and used in space.

Or just used as an upper stage! See https://en.wikipedia.org/wiki/Saturn_C-5N, for instance, and a bunch of even more ridiculous Soviet designs.

Amazingly, this project (nuclear third stage for Saturn V) was actually under serious development. This to be used on a rocket stack which had had two major incidents in 13 launches; it really was a very different safety culture back then.