NASA's Evolutionary Xenon Thruster (NEXT) Component Verification Testing

‡Component testing is a critical facet of the comprehensive thruster life validation strategy devised by the NASA’s Evolutionary Xenon Thruster (NEXT) program. Component testing to-date has consisted of long-duration high voltage propellant isolator and high-cycle heater life validation testing. The high voltage propellant isolator, a heritage design, will be operated under different environmental condition in the NEXT ion thruster requiring verification testing. The life test of two NEXT isolators was initiated with comparable voltage and pressure conditions with a higher temperature than measured for the NEXT prototype-model thruster. To date the NEXT isolators have accumulated 18,300 hours of operation. Measurements indicate a negligible increase in leakage current over the testing duration to date. NEXT ½” heaters, whose manufacturing and control processes have heritage, were selected for verification testing based upon the change in physical dimensions resulting in a higher operating voltage as well as potential differences in thermal environment. The heater fabrication processes, developed for the International Space Station (ISS) plasma contactor hollow cathode assembly, were utilized with modification of heater dimensions to accommodate a larger cathode. Cyclic testing of five ½” diameter heaters was initiated to validate these modified fabrication processes while retaining high reliability heaters. To date two of the heaters have been cycled to 10,000 cycles and suspended to preserve hardware. Three of the heaters have been cycled to failure giving a B10 life of 12,615 cycles, approximately 6,000 more cycles than the established qualification B10 life of the ISS plasma contactor heaters. Nomenclature B1 = statistical number of cycles in which 1% of components are expected to fail with 90% Confidence B10 = statistical number of cycles in which 10% of components are expected to fail with 90% Confidence F(t) = fraction of units failing t = cycles to failure t0 = origin of distribution η = characteristic life or scale parameter β = slope or shape parameter