Environmental Testing of NASA's Evolutionary Xenon Thruster Prototype Model 1 Reworked Ion Engine

NASA's Evolutionary Xenon Thruster propulsion system is an advanced ion propulsion system that is oriented toward robotic exploration of the solar system using solar electric power. The subsystem includes an ion engine, a power processing unit, feed system components, and a thruster gimbal. The prototype model engine, PM1, was subjected to qualification-level environmental testing to demonstrate compatibility with environments representative of anticipated mission requirements. Although the testing was largely successful, several issues were identified, including the fragmentation of potting cement on the discharge and neutralizer cathode heater terminations during vibration, which led to abbreviated thermal testing, and the generation of particulate contamination from manufacturing processes and engine materials. The engine was reworked to address most of these findings and renamed PM1R, and the environmental test sequence was repeated. Thruster functional testing was performed before and after the vibration and thermal-vacuum tests. Random vibration testing, conducted with the thruster mated to the breadboard gimbal, was executed at 10.0 g(rms) for 2 min in each of the three axes. Thermal-vacuum testing included three thermal cycles from -120 to 215 degrees C with hot engine restarts. Thruster performance was nominal throughout the test program, with minor variations in a few engine operating parameters likely caused by facility effects. There were no significant changes in engine performance as characterized by the engine operating parameters, ion optics performance measurements, and beam current density measurements, indicating no significant changes to the hardware as a result of the environmental testing. The redesigned cathode heater terminations successfully survived the vibration environments. NASA's Evolutionary Xenon Thruster PM1R engine and the breadboard gimbal were found to be well designed to meet environmental requirements based on the results reported herein.