PERFORMANCE EVALUATION AND OPTIMIZATION OF AN 8-GHz MICROWAVE ELECTROTHERMAL THRUSTER
Open Access
- Author:
- Blum, Jacob
- Graduate Program:
- Aerospace Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- None
- Committee Members:
- Michael Matthew Micci, Thesis Advisor/Co-Advisor
Michael Matthew Micci, Thesis Advisor/Co-Advisor - Keywords:
- MET
microwave electrothermal thruster
electric propulsion
aerospace engineering - Abstract:
- The performance of an 8-GHz microwave electrothermal thruster was measured using various thrust stand configurations with nitrogen gas as the propellant. The momentum of the exhausted propellant was transferred to the flexible beam by either a momentum trap or a deflection cone. The thrust stand used either a strain gauge or an optical distance sensor to measure the deflection of the flexible beam, which was ultimately converted into thrust measurements. The thruster was also optimized by parametrically testing a variety of different thruster components, including antenna depth, propellant injector cross-sectional diameter, nozzle material and throat diameter, and propellant gas type. Input powers ranging from 100 W to 350 W were used to induce electrical breakdown of the propellant gas (nitrogen, ammonia, and simulated decomposed hydrazine) and form a coalesced plasma. The thrust stand configuration that used a strain gauge and momentum trap produced thrust values within 3% of the theoretically calculated thrust. However, this configuration could not measure low thrust values. The thrust stand configuration that used a strain gauge and deflection cone was able to measure low thrust values; however, the thrust measurement procedure illustrated measurement contradictions, producing thrust values within both 0.7% and 11% of theoretical thrust values. The thrust stand configuration using the deflection cone and optical distance sensor eliminated the measurement contradictions; however, the configuration continued to provide thrust measurements that differed from the theoretical thrust calculations by upwards of 12%. The thruster configuration that achieved the highest specific impulse, thermal efficiency, and thruster efficiency is considered the optimal configuration. This experimentally determined optimal configuration used ammonia propellant and consisted of a two piece chamber separated by a separation plate; an antenna with a flat tip and a protruding depth 75% reduced from the baseline configuration; the smallest possible propellant injector diameter that does not choke the flow; and a stainless steel nozzle with a throat diameter 235% greater than the baseline nozzle throat diameter. This produced thermal and thruster efficiencies of approximately 75% and a specific impulse 33% higher than the highest specific impulse ever achieved by any microwave electrothermal thruster experiment using ammonia as the propellant. Recommendations for achieving more accurate thrust measurements as well as further thruster optimization are also discussed.