BPT-4000 Hall Thruster Extended Power Throttling Range Characterization for NASA Science Missions

Abstract

Commercial electric propulsion systems are now being considered as a cost effective solution for competitively awarded science missions such as the NASA Discovery and New Frontiers programs. Aerojet’s BPT-4000 Hall thruster, which has been identified as a candidate for near-term use on NASA science missions, has recently completed a 6,750 h qualification life test that demonstrated power throttling from 1 to 4.5 kW. To assess the suitability of extending the operating range further, a test campaign designed to assess the performance and plasma properties of the BPT-4000 over an extended throttling range has been implemented. An inverted-pendulum thrust stand is used for performance measurements. In the near-field plume, an emissive probe, cylindrical Langmuir probe, and current density probes are deployed to measure plasma potential, plasma density, electron temperature, and ion current density. In the far-field plume, an RPA, ExB probe, and emissive probe are used to measure the ion energy, ion species’ fractions, and plasma potential. The test campaign has demonstrated a 30X power throttling range from 0.15 to 4.5 kW, corresponding to discharge voltages of 125 to 700 V and discharge currents of 1 to 15 A. An eight hour firing demonstrated uninterrupted operation of the thruster at 0.25 kW (150 V, 1.67 A). At this operating condition, the voltage and current were 20% and 67%, respectively, above the minimum power operating condition of 150 V, 1.0 A that the thruster was operated at during the test campaign. The cathode remained healthy throughout testing and was capable of operating without a heater or keeper despite the currents required while at lowpower. An initial assessment of the thruster operating at discharge voltages in excess of 400 V has demonstrated the growth potential of this thruster to operate efficiently at specific impulses greater than 2500 s.