Application of high power millimeter-wave to space propulsion

A microwave beaming thruster boosted by a 170GHz gyrotron was investigated. Plasma was successfully initiated by focusing the millimetre wave beam using a parabolic reflector. The plasma propagation velocity was increased with the beam power density; the velocity became supersonic at the power density beyond 80 kW/cm/sup 2/. Propulsive impulse was measured through the flight experiments, and resulting momentum coupling coefficient, a ratio of thrust to input energy, was found drastically increased when the plasma propagation velocity becomes supersonic.