I think nuclear propulsion is there only way forward for interplanetary colonisation because we've long reached the limits of chemical. And ion is too slow.
Now talking speculative fiction, the real breakthrough will come if we figure out a way to induce acceleration without an action-reaction process. Just an energy source, and no propellant. Being able to sustain 1g for a few months on a heavy spacecraft means interstellar travel (proxima centaury) would be within grasp.
Anyone have info on how they’re improving on NERVA?
https://en.wikipedia.org/wiki/Nuclear_salt-water_rocket
Scott Manley video on the subject: https://www.youtube.com/watch?v=cvZjhWE-3zM
Basically a controlled thermo nuclear reaction blasting out the back.
"One design would generate 13 meganewtons of thrust at 66 km/s exhaust velocity (or 6,730 seconds ISP compared to ~4.5 km/s (450 s ISP) exhaust velocity for the best chemical rockets of today)."
You certainly wouldn't want to use this to take off from Earth. But we could use it for deep space travel.
People get upset enough about reactors that don’t move and live inside huge structures of reinforced concrete. Can we convince this segment of the population that launching a small device (with necessarily less shielding) is safe?
Even the most reliable launch vehicles (Falcon 9, Atlas V) are probably not more than ~99% likely to succeed. Can the payload be made safe in the event that it fails to make orbit?