Status of the Next Ion Thruster Long Duration Test

Abstract

Abstract The status of NASA’s Evolutionary Xenon Thruster (NEXT) Long Duration Test (LDT) is presented. The test will be conducted with a 36 cm diameter engineering model ion thruster, designated EM3, to validate and qualify the NEXT thruster propellant throughput capability of 450 kg xenon. The ion thruster will be operated at various input powers from the NEXT throttle table. Pretest performance assessments demonstrated that EM3 satisfies all thruster performance requirements. As of June 26, 2005, the ion thruster has accumulated 493 hours of operation and processed 10.2 kg of xenon at a thruster input power of 6.9 kW. Overall ion thruster performance, which includes thrust, thruster input power, specific impulse, and thrust efficiency, has been steady to date with very little variation in performance parameters. I. Introduction The 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 (refs. 1 and 2). While the 2.3 kW NSTAR ion thruster input power and service life capabilities are appropriate for Discovery Class as well as other, smaller NASA missions, the application of NSTAR hardware to more demanding missions such as outer planet explorers and sample return missions is limited due its lack of power and total impulse capability. As a result, NASA’s Office of Space Science awarded a development project to a NASA Glenn Research Center (GRC)-led team to develop the next generation ion propulsion system (refs. 3 and 4). The propulsion system, called NASA’s Evolutionary Xenon Thruster (NEXT), consists of a 36 cm beam extraction diameter ion thruster, a lightweight, modular power processing unit with an efficiency and a specific mass equal-to or better-than the NSTAR power processor, and a xenon feed system that will significantly reduce mass and volume relative to the NSTAR feed system. Ion thruster performance requirements include a specific impulse of at least 4050 s at full power and a thruster efficiency of greater than 0.63 at full power. Regarding service life, the ion thruster must provide a 185 kg baseline requirement and a 300 kg nominal mission requirement xenon throughput capability. Therefore, based on the nominal mission requirement, the ion thruster must provide a 450 kg qualification throughput (ref. 5). The first wear test of a NEXT ion thruster was for a 2038 hour duration at full power and processed 43 kg of xenon (ref. 6). The service life capability of the NEXT ion thruster is being assessed by thruster wear tests and life-modeling of critical thruster components, such as the ion optics and cathodes. The maximum thruster input power level was chosen for the first 300 kg of propellant throughput because life-modeling predicted that this power level will cause the most severe thruster erosion. The objectives of the LDT include: characterizing thruster operation and performance over the duration of the test; identifying thruster life-limiting phenomena; and measuring thruster component wear rates and comparing them with that predicted from life models. In addition, after 300 kg propellant throughput has been achieved the thruster will be throttled into a design reference mission profile until qualification level propellant throughput has been demonstrated (ref. 5). This paper presents the status of the NEXT LDT. A description of the test article is discussed followed by a description of the test support hardware, which includes the power console, gas feed system, vacuum facility, and diagnostics. The test operating condition is then described. Finally, wear test results to date are presented and discussed.