Mitchell L. R. Walker

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This article presents the theory and operation of a null-type, inverted pendulum thrust stand. The thrust stand design supports thrusters having a total mass up to 250 kg and measures thrust over a range of 1 mN to 5 N. The design uses a conventional inverted pendulum to increase sensitivity, coupled with a null-type feature to eliminate thrust alignment(More)
As part of a larger e↵ort by the American Institute of Aeronautics and Astronautics (AIAA) Electric Propulsion Technical Committee to provide standards for electric thruster measurement and test, we have been developing recommended practices for direct thrust measurements. Measurement of thrust is the most fundamental requirement in thruster performance(More)
The effects of dissimilar probe design and facility backpressure on the measured ion current densities of Hall thrusters are investigated. JPL and GRC designed nude Faraday probes are used to simultaneously measure the ion current density of a 5 kW Hall thruster in the Large Vacuum Test Facility (LVTF) at the University of Michigan. The probes are located(More)
A neutral gas background pressure map of the Large Vacuum Test Facility (LVTF) at the University of Michigan is presented. The LVTF was mapped at a series of cold anode flow rates corresponding to P5 Hall thruster operating conditions of 1.5, 3.0, and 9.0 kW. The chamber pressure was mapped at nominal xenon pumping speeds of 140,000 and 240,000 l/s with a(More)
The ability of a magnetically-filtered Faraday probe (MFFP) to obtain the ion current density profile of a Hall thruster is investigated. The MFFP is designed to eliminate the collection of low energy, charge-exchange (CEX) ions by using a variable magnetic field as an ion filter. In this study, a MFFP, boxed Faraday probe (BFP), and nude Faraday probe are(More)
A neutral background pressure map of the Large Vacuum Test Facility (LVTF) at the University of Michigan is presented. The LVTF was mapped at hot anode (i.e., discharge on) flow rates of 5.25 and 10.46 mg/s, corresponding to P5 Hall thruster operating conditions of 1.5 and 3.0 kW. The chamber pressure was mapped at nominal xenon pumping speeds of 140,000(More)
A rf power system has been developed, which allows the use of rf plasma devices in an electric propulsion test facility without excessive noise pollution in thruster diagnostics. Of particular importance are thrust stand measurements, which were previously impossible due to noise. Three major changes were made to the rf power system: first, the cable(More)
TECHNICAL NOTES are short manuscripts describing new developments or important results of a preliminary nature. These Notes cannot exceed 6 manuscript pages and 3 figures; a page of text may be substituted for a figure and vice versa. After informal review by the editors, they may be published within a few months of the date of receipt. Style requirements(More)