PROSPECTS FOR MICROWAVE HEATED PROPULSION.

The utilization of microwave energy in an electrothermal thruster scheme to heat gases to high temperatures followed by a nozzle expansion was examined. Hydrogen is the propellant of choice since it produces the highest exhaust velocity for a given chamber temperature, however, hydrogen does suffer frozen flow losses which are discussed. Five schemes for the absorption of microwave radiation in a high pressure gas are identified with two schemes being capable of isolating the high temperature gas region from material walls. Experimental evidence exists showing almost complete microwave absorption by the gas as well as hydrogen gas temperatures up to 9000 K equating to a specific impulse of 2000 seconds including frozen flow losses. The generation of microwave energy can be accomplished with electrical efficiencies approaching 85%, making the on-board generation of the microwaver power feasible.