Physical Insight into Microwave Electrothermal Thruster Startup via Multi-Objective Design Optimization and Plasma Simulation

Microwave Electrothermal Thrusters are an effective and affordable space propulsion technology for small spacecraft platforms. They offer various advantages including operational lifetime, fuel efficiency, and fuel selection over other types of electrothermal thrusters. However, due to the complex physical mechanisms associated with multi-physics involved, there is still room left for optimization to achieve higher performance with reduced power. The present study consists of two steps; (1) multi-objective design optimization based on electromagnetic simulations; (2) assess the optimized geometries in plasma simulation. Focusing on the incipient stage of plasma ignition, the present study investigates how the electric field strength and bandwidth of the optimized resonator geometries correlate with the process of plasma generation. The plasma simulations are conducted for two types of propellants, namely argon and water vapor. The results show that these optimal geometries have sufficiently strong electric fields for both types of propellant to ignite plasma, and the evaluation of the plasma is related to the electric field and bandwidth.