Review of alternative propellants in Hall thrusters

Hall thrusters, the most common type of electric propulsion system, typically use xenon as the propellant, given its inertness, its ability to be stored at a high density under pressure, and good thrust to power ratio coupled with a high specific impulse compared to chemical propulsion. However, the number of satellites utilizing electric propulsion units and particularly Hall thrusters is dramatically increasing, resulting in a strain on the availability of xenon propellant in the context of a volatile noble gas market. This phenomenon is seen with the dawn of large satellite constellations and the accelerated launch rate of satellite units, the majority of which now use a Hall thruster as their primary propulsion system. Alternatives to xenon are available in the form of other noble gases, molecular propellants and condensable elements. Such propellants offer certain advantages in terms of specific mission scenarios, or for certain propulsion system sizes. This paper represents a review of alternatives to the conventional xenon propellant for Hall thrusters, providing a comparative study of the most feasible alternatives. Various considerations of using alternative propellants are outlined, and a comprehensive database of experimentally measured Hall thruster performance is compiled to pair the measured performance using various propellants to the results of a theoretical propellant performance estimation.