Development of a national thrust test facility for electric propulsion at Robinson Research Institute, New Zealand

Abstract

The Robinson Research Institute is developing a type of electric propulsion for spacecraft called an applied-field magneto-plasma-dynamic (AF-MPD) thruster. The applied field module of the thruster features a cryocooler-cooled high-temperature-superconducting (HTS) magnet generating central fields exceeding 1 Tesla. This paper reports on the progress to date of the thruster test facilities established at the Institute to enable development of the AF-MPD and electric propulsion in general. The vacuum facilities consist primarily of a 1 m diameter, 3 m3 cylindrical chamber with a high-vacuum pumping speed, measured to be about 4200 L/s (Ar). The chamber can be reduced from atmospheric pressure to 1E10-5 hPa in about 2 h, enabling a rapid testing turn-around time, and maintains 5E10-4 hPa during thruster operation at typical mass flow rates of 5 mg/s (Ar). A pendulum thrust-stand has been purpose built to withstands static thruster loads of up to 30 kg and measure thrust forces up to 200 mN. It is also designed to be inherently insensitive to the unique challenges of measuring AF-MPD with superconducting magnets; strong magnetic fields, cryocooler vibration, and the thermal gradients. Initial thrust-stand testing, whilst implementing both water-cooling and a cryocooler showed it to be capable of measuring forces to a precision of approximately 1 mN and with an absolute accuracy of +/-2.3 mN (full scale). An extensive suite of software tools has also been developed to coordinate the large set of instruments needed to run the vacuum facilities, the thrust-stand, HTS magnet and cryocooler in addition to the many other auxiliary- and logging systems. Various upgrades to the facilities are in progress or planned.