Microwave electrothermal propulsion for space

The microwave electrothermal thruster (MET) is attractive for medium- or high-power spacecraft propulsion. A propellant gas is heated by passing it through a microwave plasma discharge created in a resonant cavity by tuning either the TM(011) or the TM(012) mode for impedance-matched operation. The MET is electrodeless, synergistically combines high pressure and high power capability, provides external control over the energy-conversion discharge, and operates on hydrogen propellant. Upwards of 95% efficiency has been reported. Calculations of potential MET performance are reported. Apparatus for testing the MET to power levels of 30 kW at 915 MHz is described. The low-ripple operation of the microwave generator has been verified, as has a procedure for starting the microwave discharge and raising the power applied to the cavity. Impedance-matched resonant operation of the microwave cavity has been achieved