A nuclear salt water rocket works similar to chemical rockets except it uses nuclear reactions instead of chemical reactions. here is a video
https://www.youtube.com/watch?v=cvZjhWE-3zM for the uninitiated. It is the most plausible propulsion system we could build in the near future that is really powerful.
It is much better than a regular rocket, it can go up to 1% the speed of light in a few days. But fusion reactions can get you up to 15% light speed, and at that speed you can reach the nearest star system in about 30 years.
So is it possible to modify the salt water rocket to inject heavy-water pellets into the fission plume to get secondary fusion reactions.