Fundamental Limitations of Rotating Magnetic Field Thrusters

Abstract

This dissertation investigates the challenges in achieving high efficiency for rotating magnetic field (RMF) thrusters. These thrusters are a novel form of in-space electric propulsion aimed towards high power applications (>100 kW) and operation on non-traditional propellants such as air, water, or carbon dioxide. These capabilities could enable missions such as air-breathing satellites in very low earth orbit, cargo transportation to Mars, or rapid repositioning in cis lunar space. RMF thrusters may be well suited to these applications; however, the efficiency of research prototypes remains low at around 1%, whereas state-of-the-art electric thrusters reach upwards of 60%.

This work showcases the development of several RMF thruster prototypes with the aim of characterizing their performance and improving their efficiency. Analysis of the overall propulsive efficiency of the initial RMF thruster prototype was conducted using plasma diagnostic probes. This analysis revealed that the RMF thruster is severely limited in its ability to convert power coupled into the propellant into an energetic beam, and the majority of the power is lost through visible light.

Because of this result, an updated thruster was constructed to operate continuously, instead of the typical discrete pulsed operation. This operational regime was found to raise propulsive efficiency by a factor of over 400%; however, the overall thruster efficiency still only reached a maximum of just under 3%. To further explain the performance of these thrusters, an analytical performance model was development to predict performance in the continuous mode. This model agrees with the present experimental results and predicts RMF thruster efficiency of up to 65% through critical design changes to the device.

This effort marks the first comprehensive diagnostic evaluation of RMF thrusters, the first operation of an RMF thruster in the continuous mode, and an updated inferred maximum theoretical efficiency for this technology.