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The Effects of Background Pressure on SPT-140 Thruster Performance at Multiple Power LevelsNASA's planned Psyche mission is scheduled to launch in 2022 and begin a 3.5-year cruise to the metallic asteroid Psyche, where it would examine this unique body. The baseline spacecraft design is a hybrid of JPL's deep-space heritage subsystems with commercial partner SSL's power, structure, and SPT-140 electric propulsion subsystems. Since the deep-space implementation of the SPT-140 differs from the commercial implementation, primarily in the need for deep power throttling, characterization of the system at lower powers is necessary. One specific area of interest is the sensitivity of thruster performance to background pressure in ground-based test facilities, which can have an impact on the prediction of in-space performance. Measurements of this pressure dependence were performed on a qualification-model SPT-140 thruster over the 0.9-4.5 kW range of interest for the Psyche mission. Thrust sensitivity to pressure, in an absolute sense, was largest at 4.5 kW and decreased with power until there was little-to-no measurable effect at 0.9 kW. In a relative sense, thrust sensitivity was similar at all powers above 0.9 kW with about 2-4% higher thrust measured at 10 μTorr than at the lowest operating pressure. Thruster stability margin, examined as a function of magnet current, did not have a strong dependence on facility pressure. Finally, an investigation of low-power operation at the lowest facility pressure showed that a combination of added cathode keeper current and additional cathode propellant flow significantly mitigated the larger negative cathode-to-ground voltages that were observed. These test results, combined with thruster life test results, inform the selection of proper low-power operating conditions for Psyche.
Document ID
20180005324
Document Type
Conference Paper
Authors
Snyder, John S. (Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Lenguito, Giiovanni (Space Systems/Loral Palo Alto, CA, United States)
Frieman, Jason D. (NASA Glenn Research Center Cleveland, OH, United States)
Haag, Thomas W. (NASA Glenn Research Center Cleveland, OH, United States)
Mackey, Jonathan A. (NASA Glenn Research Center Cleveland, OH, United States)
Date Acquired
September 17, 2018
Publication Date
July 9, 2018
Subject Category
Spacecraft Propulsion and Power
Report/Patent Number
GRC-E-DAA-TN57023
Meeting Information
AIAA/SAE/ASEE Joint Propulsion Conference(Cincinnati, OH)
Funding Number(s)
WBS: WBS 302584.02.01
CONTRACT_GRANT: NNN12AA01C
Distribution Limits
Public
Copyright
Public Use Permitted.

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