http://en.wikipedia.org/wiki/Magnetoplasmadynamic_thruster http://en.wikipedia.org/wiki/Magnetoplasmadynamic_thruster We also have these; it's probably more pr

http://en.wikipedia.org/wiki/Magnetoplasmadynamic_thruster http://en.wikipedia.org/wiki/Magnetoplasmadynamic_thruster We also have these; it's probably more practical, but it still requires a powerful onboard reactor (in practice, probably fission or fusion).