Directly measuring thrust from a superconducting applied field magnetoplasmadynamic thruster

Abstract

The use of superconducting magnets with electric propulsion systems, such as applied-field magnetoplasmadynamic thrusters (AF-MPDTs), presents opportunities to study the relevant physics and scaling relationships to higher magnetic fields as well as improving the feasibility of using such thrusters on space-craft due to a potential size, weight and power reduction of the magnet system. A critical characterization of an electric propulsion system is its thrust, favoring a direct measurement to reduce uncertainty in the measurement’s accuracy. A superconducting magnet subsystem will present several additional challenges to this already challenging task. For a superconducting magnet to operate correctly it needs to be kept at cryogenic temperatures (<80 K), which for a space-bound system will be achieved via a mechanical cryocooler. The vibrations from such a cryocooler, combined with the stray field from the magnet, will impact the thrust measurement apparatus. The Robinson Research Institute (RRI) undertakes fundamental and applied superconductivity research, and has recently embarked on an AF-MPDT research program. The project involves an in-space demonstration of a superconducting magnet subsystem, and the development of a ground-based, kW-class superconducting AF-MPDT with applied fields of 1 T along with the establishment of ground test facilities. At DLR Göttingen, electric propulsion is tested for commercial and scientific customers which includes the development of electric propulsion diagnostics as well as thrusters. Test facilities include multiple thrust balances, one of these balances is an inverted double-pendulum based on a set of quartz glass rods, which has been used to measure different thrusters. This paper describes a collaborative project between RRI and DLR-Göttingen to develop direct, accurate thrust measurement capability of superconducting AF-MPDT. The project will also cross-validate measurement systems at our respective facilities and quantify the impact of vacuum-chamber size and background pressure.