The results of the NEXT 2000 h wear test are presented. This test was conducted with a 40 cm engineering model ion engine, designated EM1, at a 3.52 A beam current and 1800 V beam power supply voltage. Performance tests, which were conducted over a throttling range of 1.1 to 6.9 kW throughout the wear test, demonstrated that EM1 satisfied all thruster performance requirements. The ion engine accumulated 2038 h of operation at a thruster input power of 6.9 kW, processing 43 kg of xenon. Overall ion engine performance, which includes thrust, thruster input power, specific impulse, and thrust efficiency, was steady with no indications of performance degradation. The ion engine was also inspected following the test. This paper presents these findings. I. IntroductionThe success of the NASA Solar Electric Propulsion Technology Applications Readiness (NSTAR) program's ion propulsion system on the Deep-Space 1 spacecraft has secured the future for ion propulsion technology for other NASA missions.1 While the 2.3 kW NSTAR ion engine input power and service life capabilities are appropriate for low power missions, in-space propulsion technology analyses conducted by NASA identified the need for a higher power, higher throughput capability 25 kW ion propulsion system targeted for robotic exploration of the outer planets. As a result, NASA's Office of Space Science awarded a research project to a NASA Glenn Research Center (GRC)-led team to develop the next generation ion propulsion system. 2,3 The propulsion system, called NASA's Evolutionary Xenon Thruster (NEXT), consists of a 40 cm diameter ion engine, a lightweight, modular power processing unit with an efficiency and a specific power equal-to or better-than the NSTAR power processor, and a xenon feed system which uses proportional valves and thermal throttles to significantly reduce mass and volume relative to the NSTAR feed system.Ion engine performance requirements include a specific impulse and thruster efficiency of at least 4050 and 0.67, respectively, at full power. Based on NEXT Phase 1 design reference missions, the ion engine must provide a 270 kg propellant throughput capability at full power, which ultimately results in a 405 kg qualification throughput requirement.The service life capability of the NEXT ion engine is being assessed by engine wear tests and modeling of critical engine components, such as the ion optics and cathodes. The first wear test of a NEXT ion engine was planned for a 2000 hour duration at a 6.9 kW input power. The highest thruster input power level was chosen because modeling has predicted that this power level will cause the severest engine erosion. The objectives of this early wear test included: characterizing thruster operation and performance over the duration of the test; identifying thruster life-limiting phenomena; and measuring critical thruster component wear rates.This paper presents the results of the first NEXT wear test. A description of the test article is discussed in the next section. This is followed by a descripti...

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During a component compatibility test of the NASA HiVHAc Hall thruster, a number of plasma diagnostics were implemented to study the effect of varying facility background pressure on thruster operation. These diagnostics characterized the thruster performance, the plume, and the plasma oscillations in the thruster. Thruster performance and plume characteristics as functions of background pressure were previously published. This paper focuses on changes in the plasma oscillation characteristics with changing background pressure. The diagnostics used to study plasma oscillations include a high-speed camera and a set of high-speed Langmuir probes. The results show a rise in the oscillation frequency of the "breathing" mode with rising background pressure, which is hypothesized to be due to a shortening acceleration/ionization zone. An attempt is made to apply a simplified ingestion model to the data. The combined results are used to estimate the maximum acceptable background pressure for performance and wear testing.

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analysis of the discharge current waveforms showed that increasing the vacuum chamber background pressure resulted in a higher discharge current dominant breathing mode frequency. Finally, IVB maps of the TDU-1 thruster indicated that the discharge current became more oscillatory with higher discharge current peak-to-peak and RMS values with increased facility background pressure at lower thruster mass flow rates; thruster operation at higher flow rates resulted in less change to the thruster's IVB characteristics with elevated background pressure.