Colloid microthruster system life test

Abstract

Results from over 1750 hr of microthruster system operation are presented. The system consists of a three-needle thruster, bare tungsten wire filament neutralize!*, bladderless blow- down propellant feed system, and 5-w power and signal conditioning unit. Neutralizer opera- tion was terminated after 950 hr because of electron leakage to high voltage through some insulator holes. The test was stopped when expulsion pressure was lost from the trapped volume of pressurizing gas in the feed system. Normal operation at 8-/xlb thrust and 950-sec specific impulse demonstrated extremely smooth steady-state performance and reproducible turn-on and turn-off characteristics. mass-flow measurements were made with this system by weighing it before and after 166 hr operation. The measured mass flow was 15% lower than the average computed time-of-flight mass flow, but only 0.3% higher than the calibrated mass- flow data previously reported.2-3 Acceleration and vibration tests to Titan III-C booster vehicle requirements were conducted. After vibration, the feed line to the thruster was found severed at its coupling. The coupling was not used in subsequent design. Electromagnetic compatibility characteristics of the sys- tem were compared with MIL-STD-461A specifications. It was concluded that lightweight, readily available components could be inserted between a spacecraft power source and the input inverter to the power conditioning unit to effectively suppress electromagnetic conduction. The microthruster complied with specification limits for electromagnetic emis- sions from its exhaust beam. The yaw control configuration thermal analysis was per- formed for a three-axis stabilized spacecraft in synchronous equatorial orbit. Thruster heater peak and average power levels required to maintain the needles at given operating conditions were determined from the analysis. This in- formation impacted on subsequent system design. Based on engineering data obtained from the earlier micro- thruster system, a single-thruste r, flight-protot ype system was developed. of life testing. This paper presents the results of 1792 hr