The problem with this, I suppose, must be the power plant needed to produce the electric power needed to drive the fusor. My guess is that for a deep space shi

The problem with this, I suppose, must be the power plant needed to produce the electric power needed to drive the fusor. My guess is that for a deep space ship one would need a propellant-cooled fission reactor, while for a thruster for orbit management a solar/battery/capacitor system might suffice (but with very short run times). For a deep space system there would be challenges. Shutting down the fission reactor would require continuing to use propellant as coolant long after the fusor stops working -that or a massive radiator-, and either way the net ISP would be driven down. And then the fission reactor would have to stay shut down for quite some time. Though if you jettison the fission reactor when propellant runs out then there are no such problems! For orbit management thrusting though this might yield a very weight-efficient system!