How small can you make a nuclear weapon?

 

YouTube video by Curious Droid

Comment:

He mentions the objections that would arise if such were actually proposed for use in spacecraft propulsion. The advantages would be in increasing ISP, which determines the amount of propellant mass needed. A nuclear device may have an ISP hundreds of times greater than the best chemical engines.

There was a proposal to do atomic propulsion back in the fifties, but the idea is moot since it is outlawed by international treaty.

Nevertheless, it is an intriguing idea, which forms the basis of the Jumbo sized Aldrin Cycler. You could transport a massive structure out there using atomic propulsion. Once out there in its orbit around Mars and Earth, it could be used to transport lots of people and cargo to the Red Planet.