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Atomspheric discharge using a high power millimeter wave and its application to rocket propulsion

Microwave Rocket is an application of atmospheric discharge using a high power millimeter-wave beam. When a high power pulsed millimeter-wave beam is provided into a focusing reflector, atmospheric discharge arises in the vicinity of the focal point. The induced plasma absorbs the following part of the millimeter-wave pulse and propagates towards the beam source while generating a shock wave. The shock wave drives impulsive thrust. Because propulsive energy is provided by a microwave beam transmitted from outside, the vehicle is not necessary to load an energy source by itself. In this study, pressure histories in the thruster were measured under the 20Hz and 50Hz repetitive-pulse operation of 1sec duration. The shock wave is formed at each pulse and the thrust impulse is generated. Thrust impulses were estimated from pressure history. The thrust impulse was smaller than impulse at the first pulse and thrust impulse becomes steady at latter pulses. As a result, the steady operation was achieved in both frequencies. The 1sec duration operation with 50Hz repetition frequency was conducted with a thruster mounted on a movable stand. From the trajectory measured by a laser displacement gauge, the thruster was found to have moved at the constant acceleration motion. The acceleration and thrust force were estimated a=1.6m/s2 and F=3.4N, respectively. The thrusts estimated from the pressure history and from the trajectory showed a good agreement.