[BenLurkin]

One idea is for a nuclear-powered engine that magnetically accelerates plasma-gas with molecules which are electrically charged.

Isn't that what used to be called "Ion Drive"?

[RightWhale]

Isn't that what used to be called "Ion Drive"?

Ion or plasma motors. The power supply could be solar. Of course, if the ion propulsion is stronger than butterfly wings, nuclear would do well. Interstellar would have to be nuclear.