AD Astra Rocket had an agreement with NASA  to develop a powerful plasma engine with a variable impulse, the VASIMR (Variable Specific Impulse Magnetoplasma Rocket).

-See also the Franklin (Frank) Chang chapter in an apendix of this work.

The engine that is being tested at the moment is the VX-200
Thanks to the new technologies on superconductors which are necessary for the electro magnets that accelerate the engine's exhaust.

"Vasimr plasma engine"

-The fuel it uses is hidrogen or helium as gas that is ionized in coils and launched by the high velocity nozzle. Compared with a classic rocket engine the weight of the needed fuel goes from 7.5 tons to 300kgs. They reach very high temperatures.

"Testing a VASIMR"