On a related note, lets also look at the nuclear salt-water rocket - arguably the king of crazy (yet theoretically viable) on the nuclear rocket field right now:
Similar to https://en.wikipedia.org/wiki/Magneto-inertial_fusion
The exhaust is clean, because the system is closed.
Also it reminds me of some descriptions of so called 'Vimanas' which occur in old Indian scriptures, and nerdy people from today tried to reconstruct/reverse engineer/remimagine what's described in there.
And this fits, perfectly so.
Edit: I think of this as even more terrifying thant that saltwater thing:
https://en.wikipedia.org/wiki/Fission-fragment_rocket
Would you trust in this evil trickster dust? ;->
Actually, I kinda think it demonstrates we really are not done with nuclear engines & even better, more crazy and higher performance propulsion methods will show up. And also, we really need to finally start building some of them them! :)
Like, even some simple NERVA or NEP would be at least a start. :)
1) it is achievable with 1960s technology
2) the payloads, my god, MILLIONS of tons is the ideal cargo size
3) one month to get to jupiter's moons!
I think if we had good funding I would do:
1) Get starship mature
2) capture some asteroids to make an orbital base
3) moon base + a lunar launch loop or launch rail or lunar space elevator
4) build an orion ship on the moon and launch from the moon
5) mine the major asteroids. Profit!
https://en.wikipedia.org/wiki/Nuclear_lightbulb
is more inspiring to me.