Originally Posted By: Momos

I don't know the figures for VASIMIR and co, but it all sounds very unlikely. Either we need lots of propellant or a really big nuclear power plant.

But that's the point of vasimr - you use a nuclear reactor to provide the kinetic energy you impart on your fuel. You can get extremely high ISP's that way, thus cutting your fuel bill. At the highest efficiency settings (low-thrust, but high exhaust velocity), I've read predictions that VASIMR may have higher ISP's than any other potential tech aside from anti-matter.