Single-Channel Hollow Cathodes in 5–20-eV Argon Discharge for Spacecraft Thruster Applications

High-power magnetoplasmadynamic (MPD) thrusters are an attractive option for providing primary propulsion on flagship-class spaceflight missions beyond the Low Earth Orbit (LEO), such as piloted Mars and Mars cargo, and more near-term cargo missions supporting a crewed lunar outpost due to their unique ability to process large amounts of power in a relatively small footprint size. This results in significant savings in system mass and volume over competing propulsion options such as ion or Hall-effect thrusters. This paper presents a partial summary of data from recent research at the University of Southern California, in collaboration with NASA´s Jet Propulsion Laboratory, investigating several concerns of the mechanisms influencing the performance and lifetime of high-current single-channel hollow cathodes (SCHCs), the central electrode, and the primary life-limiting component in MPD thrusters. The overall objective of such research is to extend the operational lifetime of the cathode to mission-enabling lengths, generally considered to be in the range of 5-10 000 h. Specifically covered are the trends seen in the discharge efficiency and power, the size of the plasma attachment to the cathode (the active zone), the cathode exit plume plasma density and energy, and the plasma property distributions of the internal plasma column of an SCHC.