NASA has tested the EMDrive - the electromagnetic drive - in a vacuum chamber. And it still works. (But no, Daily Mail, it is not the same thing as an Alcubierre warp drive. Sigh).
If it works and scales up, it would make a trip to Mars feasible.
It will, of course, require that the ship have a nuclear power plant designed specifically for use in space. I still maintain that the best place to start in developing such is to look at the power plants currently use in submarines. And if you're worried about a nuclear reactor on your ship, again, submarines.
The next step is to test the drive in space - it's possible it's actually pushing against the Earths magnetic field. (Which could still be useful...a magnetic field based drive that produced enough specific impulse to get to orbit would be really nice).