The Combination of Two Concentric Discharge Channels into a Nested Hall-Effect Thruster.

Abstract

Hall-effect thrusters continue to be one of the most efficient technologies for spacecraft maneuvering and stationkeeping. One of the ongoing efforts in the electric propulsion community is to scale Hall-effect thrusters to high powers (10 kW - 1 MW) while maximizing performance and minimizing the thruster’s mass and size. A nested Hall-effect thruster is one configuration that can satisfy these goals, but the concept was largely untested until the development of a demonstration thruster by the University of Michigan and the Air Force Research Laboratory, with later sponsorship from the Air Force Office of Scientific Research. This prototype nested Hall-effect thruster, known as the X2, features two concentric, annular discharge channels in which xenon gas undergoes ionization and acceleration. Both discharge channels proved capable of operating separately or simultaneously using a shared hollow cathode. Performance measurements showed capabilities on par with state-of-the-art Hall- effect thrusters with additional benefits in low-voltage operation with simultaneous firing of both channels. The X2’s unique features include the availability of single-channel and dual-channel modes. The combination of all modes extends the throttling range of the X2 by allowing the exit area to vary according to the desired thrust-to-power ratio and specific impulse. This study of the X2 nested Hall-effect thruster also investigates how two simultaneously firing channels combine. Thrust measurements show a small increase in performance beyond common facility effects on electric propulsion devices. An array of plasma diagnostics provide further detail on the mechanisms that are responsible for the thrust augmentation, including changes in ion acceleration and ion beam current.