A thrust stand for direct force measurement of superconducting high-field AF-MPD thrusters

Abstract The Robinson Research Institute is developing a type of electric propulsion for spacecraft called an applied-field magneto-plasma-dynamic thruster (AF-MPD) that is operating in the 500–1500 W range using argon as the propellant. The applied field module of the thruster is a cryocooler-cooled high-temperature-superconducting (HTS) electromagnet generating a central field exceeding 1 T. Ground-based characterisation of this type of electric thruster is challenging due to the millinewton-range thrust forces from the applied field module and numerous facility effects. This paper reports on the development of a purpose-built pendulum thrust-stand able to measure millinewton thrust whilst subjected to Tesla level magnetic flux densities and the vibrational loads generated by a mechanical cryocooler—required to maintain the HTS magnet at cryogenic temperatures between 55 and 75 K. Measurement data, postprocessing methods and uncertainty calculations are presented for direct AF-MPD thrust-measurements. These demonstrate accuracies of between ±1–2 mN (1 σ ) are achievable in the 100 mN calibration range when operating an AF-MPD thruster weighting 32 kg, with a 1 T central magnetic field and with the thruster exposed to 60 Hz oscillatory accelerations peaking at ±1.47 m s −2 , generated by a mechanical cryo-cooler.