Practically, i suspect that any advantage that even small nuclear propulsion units - & the NERVA was a real piece of groundling ballast - will be more than outweighed (literally, in this case) by the support infrastructure necessary to make the system even remotely user friendly; always assuming, of course, that we can get something ressembling optimal performance from the units themselves. But then: i've analysed technology development programs over the last 40yrs to see which ones have succeeded & which ones have failed; not relied on science fantasy press releases about opening up the solar system....

Diogenes the Robert