The Variable Specific Impulse Magnetoplasma Rocket (VASIMR) is an electromagnetic thruster for spacecraft propulsion. It uses radio waves to ionize and heat a propellant. Then a magnetic field accelerates the resulting plasma to generate thrust (plasma propulsion engine). It is one of several types of spacecraft electric propulsion systems.

The VASIMR method for heating plasma was originally developed from nuclear fusion research. VASIMR is intended to bridge the gap between high-thrust, low-specific impulse and low-thrust, high-specific impulse systems. VASIMR is capable of functioning in either mode. Former NASA astronaut Franklin Chang Díaz created the VASIMR concept and has been developing it since 1977.[1]

VASIMRs units for development and test are assembled by Ad Astra Rocket Company.