Innovations in pulsed plasma thrusters to enable CubeSat science missions

Abstract

CubeSats and other small satellites in the 3-25 kg range are increasingly able to conduct meaningful science through advances in technology and miniaturization. However, much of the proposed science requires satellite mobility, which has advanced more slowly due to constraints on CubeSat launches. Pulsed Plasma Thrusters (PPTs) are a potential means of propulsion for these satellites that do not require fluid or gas tanks and feeds and are relatively compact. This makes them an ideal candidate as a low risk propulsion system for secondary payloads capable of passing safety concerns related to launch. Previously, the specific thrust, or thrust output per power input (mN/kW) of PPTs developed for space flight was low for the desired propulsion applications. This work examines the development of a PPT specifically for CubeSat propulsion. It also investigates how several science questions could be answered with these advances, with examples of missions to the asteroid belt and Europa. It is shown that the power, geometry, and propellant are influential factors that can lead to substantial gains in thruster performance. Where TeflonTM has been the propellant of choice for previously launched PPTs, the novel use of solid Sulfur propellant is demonstrated with a twofold increase in specific thrust, which is the highest of any material tested in this study. Furthermore, a switch from smooth to serrated coaxial electrodes provides an increase in the specific thrust by up to an additional factor of 2. These changes bring the current test system capabilities to 45 mN/kW with a specific impulse of 1200 sec. This provides the opportunity for CubeSat missions to execute orbital maneuvers with changes in velocity on a range from 50 to 500 m/s. A fully integrated flight model was built and tested to overcome issues arising from the transition from a benchtop system to a CubeSat formfactor and then further tested for launch and space environment compatibility. The miniaturized flight model achieves 25 mN/kW performance and is being tested on the University of Washington built HuskySat-1 3U+ CubeSat, which was launched Nov 2nd 2019 and deployed January 31st 2020.