A thruster for use with an external power supply. The thruster includes a propellant that exists in a non-gaseous state at standard temperature and pressure and has a melting point T.sub.m, a boiling point T.sub.b, and an evaporation rate. The thruster further includes a reservoir adapted to house the propellant and selectively heated to a temperature greater than T.sub.m and less than T.sub.b, and a power control mechanism positioned to control the amount of power from the external power supply being deposited into the reservoir to control the evaporation rate of the propellant.