Throttled Performance of the SPT-140 Hall Thruster

Since 2006, JPL has investigated many different commercially-available electric thruster systems for application to deep-space missions. The 4.5-kW SPT-140 Hall thruster system, now under qualification by SSL for communications satellites, carries significant heritage to SSL’s successful SPT-100 system and is attractive for many types of NASA missions. The SPT-140 qualification program is based on commercial mission requirements, however, and does not address the power throttling requirements typically needed for deep-space missions. In order to evaluate the potential of the system, a preliminary investigation of the throttled performance was conducted with a development model thruster, DM4. The thruster was operated at powers of 225 W to 6000 W to assess its performance and stability characteristics. Magnet tunings were performed across the throttle range. Performance data including thrust, specific impulse, and thruster efficiency are presented; at the 300 V, 15 A operating condition these were 281 mN, 1820 s, and 55%, respectively. Discharge current oscillations were typically 1% to 8% of the mean discharge current, and nearly independent of discharge current and voltage. Thruster operation was stable at very low powers although cathode-to-ground voltages become increasingly negative at powers less than 1000 W. This effect was mitigated by the application of additional cathode flow and cathode keeper current. Overall it was determined that the SPT-140 thruster is a viable candidate for NASA science missions and further investigation of the system is warranted.