Numerical modeling and evaluation of 8.2-GHz microwave electrothermal thruster (MET) performance using atomic and molecular gases

Microwave Electrothermal Thrusters (MET) have been proposed as a feasible electric propulsion (EP) system for micro- and nano satellites with an intermediate thrust and specific impulse range. The MET use microwave energy to heat propellant gas and sustain a plasma through collisions between free electrons and heavy particles within electromagnetic resonant cavity. This study was motivated by the need for a computational modeling that encompasses complex multi-physics of electromagnetics, fluid dynamics and plasma phenomena. We develop a 2D axisymmetric model of 8.2-GHz resonant cavity consisting of an empty and plasma section divided by a dielectric plate, and a nozzle at the end of the plasma section. In this study, we first find a resonant frequency in the absence of plasma (unloaded cavity) and implement cold gas flow without microwave power. Then we demonstrate the highly coupled effect of wave-flow-plasma phenomena in the MET discharge using helium and ammonia gases as propellants. To evaluate the MET performance, we calculate thrust and specific impulse using simulation data and perform several parametric studies. From our preliminary results, we observed that the specific impulse is dependent on the microwave input power, on the other hand, the thrust is sensitive to the mass flow rate. In our final work, comprehensive parametric studies to optimize the performance of MET will be included.