Monopropellant Thruster Exhaust Plume Contamination Measurements
Final rept. Jun 1974-Jun 1975
AIR FORCE ROCKET PROPULSION LAB EDWARDSAFB CA
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The potential spacecraft contaminants in the exhaust plume of a 0. 89N 0.2 lbf monopropellant hydrazine thruster were measured in an ultrahigh vacuum molecular sink facility. The engine plume was directed toward five quartz crystal microbalances QCMs located at angles of approximately 0, or - 15, and or - 30 degrees with respect to the nozzle centerline. The crystal temperatures were controlled such that the mass adhering to the crystal surface at temperatures of from 106 K to 256 K degrees could be measured. Thruster duty cycles of 25 ms on5 seconds off, 100 ms on10 seconds off, and 200 ms on20 seconds off were investigated. The change in contaminant production with thruster life was assessed by subjecting the thruster to a 100,000 pulse aging sequence and comparing the before and after contaminant deposition rates. The predominant contaminant at a surface temperature of 106 degrees K was postulated to be ammonia, while water and undecomposed hydrazine probably represent the primary constituents remaining on a surface at 144 degrees K. The deposits on higher temperature surfaces were much more difficult to characterize, but small amounts of water and hydrazine, which subsequently revaporize, hydrazine compounds, and aniline or aniline-derived hydrocarbons are likely candidates. Duty cycle appeared to have little effect on contaminant production except as the duty cycle influenced the average propellant flowrate. A decrease in the contaminants measured by the 144 degrees K surface and an increase in deposits on the 172 K and 200 degrees K surfaces were noted as the thruster was aged.
- Liquid Propellant Rocket Engines