The investigation of alternative solid propellants in hall effect thrusters

Abstract

This thesis documents the process of integrating metallic propellants into a stable, low-power, controllable, and scalable thruster-tank system in sub-kW Hall thrusters that can replicate gaseous propellant performance, suitable for Smallsat platform operation. A novel sublimation-based propellant storage and delivery system (PSDS) was designed, developed, and experimentally validated over 4 iterations. The first iteration labeled Mark 1 PSDS demonstrated sustained generation of the zinc gas phase by sublimation to 0.296 mg/s (6.091 SCCM). The minimum power requirement for the generation of the zinc gas phase was 30 W heat up / 10-15 W steady-state operation. A theoretical flow model was developed to estimate the transport of zinc and magnesium propellants in a given feed geometry. Mark 2 PSDS achieved zinc propellant transport up to 0.2925 ± 0.0278 mg/s (6.016 ± 0.5718 SCCM). Live load cell measurements were used to demonstrate the accuracy of the propellant flow model with an error of up to 7%. The maximum power consumption in the Mark 2 PSDS was 50 W, which included the power expenditure for preventing propellant condensation within the tank section. The third PSDS iteration, Mark 3 was designed for integration with a 100 W cylindrical Hall thruster. Mark 3 achieved a total zinc propellant output of up to 0.362 ± 0.010 mg/s (7.452 ± 0.205 SCCM) and a total magnesium output of up to 8.334 ± 0.383 mg/s (461.151 ± 21.208 SCCM) in sublimation mode. The operational power requirements when coupled to the thruster were 55 W during heat-up and 20-30 W in steady-state operation with zinc and 100 - 120 W during heat-up and estimated 100 W during steady-state operation on magnesium. A scaled version of the PSDS design was labeled Mark 4 for integration with a 350 W Hall thruster. The Mark 4 PSDS achieved 1.060 ± 0.056 mg/s (21.804 ± 1.160 SCCM) zinc propellant output at 80 - 100 W during heat-up and 70 - 80 W in steady state operation. An existing 100 W cylindrical Hall thruster was modified to pair with the Mark 3 PSDS. Zinc and magnesium operation was demonstrated below 100 W achieving a peak of 1.2 mN thrust, a specific impulse of 448 s, and an efficiency of 2.8 %. A 350 W hollow anode annular Hall thruster was designed, manufactured, and tested, demonstrating 5.0 mN, 400 s, 4.1 % anode efficiency with zinc in limited PSDS operational capacity resulting from critical manufacturing defects. Gaseous propellant performance was demonstrated at 2.7 mN, 649 s, 7.1 % efficiency with nitrogen, 9.3 mN, 1594 s, 18.1 % efficiency with argon, 14.7 mN, 1599 s, 30.5 % with krypton and 18.9 mN, 1730 s, 42.5 % efficiency with xenon.

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Identifiers

ORCID for Vlad-George Tirila: orcid.org/0000-0002-2139-2686

ORCID for Alexander Wittig: orcid.org/0000-0002-4594-0368

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