Thrust Increases in an Electron Cyclotron Resonance Thruster Using Custom Microwave Waveforms*

Low power electric propulsion is an enabling technology for many small satellite missions. Several technologies are under development with many having reached orbit over the past 2 years. Magnetic nozzle thrusters offer several potential advantages for these applications including simple operation, long lifetime, and the ability to use reactive propellants. However, their performance to date has not matched that of traditional EP technologies, with in laboratory efficiencies less than 20% at power levels under 50 watts. The current state of the art magnetic nozzle thrusters use electron cyclotron resonance to ionize and heat the propellant.

The work presented here seeks to optimize these thrusters using custom input waveforms, namely single frequency, two-frequency, and pulsed power waveforms. The input signals are generated using a broadband solid-state power amplifier with output frequencies ranging from 800-2500 MHz. Performance is measured using a sub-millinewton resolution thrust stand. By changing the waveform and keeping the geometry constant, test points can be changed while the test article is kept under vacuum, allowing hundreds of points to be tested each day. The test points are selected using a global optimization algorithm.