Performance Evaluation of the Next Ion Engine

Abstract

The performance test results of three NEXT ion engines are presented. These ion engines exhibited peak specific impulse and thrust efficiency ranges of 4060-4090 s and 0.68-0.69, respectively, at the full power point of the NEXT throttle table. The performance of the ion engines satisfied all project requirements. Beam flatness parameters were significantly improved over the NSTAR ion engine, which is expected to improve accelerator grid service life. The results of engine inlet pressure and temperature measurements are also presented. Maximum main plenum, cathode, and neutralizer pressures were 12,000 Pa, 3110 Pa, and 8540 Pa, respectively, at the full power point of the NEXT throttle table. Main plenum and cathode inlet pressures required about 6 hours to increase to steady-state, while the neutralizer required only about 0.5 hour. Steady-state engine operating temperature ranges throughout the power throttling range examined were 179-303 °C for the discharge chamber magnet rings and 132-213 °C for the ion optics mounting ring. 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 Discovery Class as well as other, smaller NASA missions, the application of NSTAR hardware to large flagship-type missions such as outer planet explorers and sample return missions is limited due its lack of power and total impulse capabilities.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), is being developed by a team composed of GRC, the Jet Propulsion Laboratory, Aerojet, Boeing Electron Dynamic Devices, Applied Physics Laboratory, University of Michigan, and Colorado State University.The NEXT propulsion system will consist 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. Each component of the propulsion system is required to achieve certain minimum performance, service life, and specific mass requirements. Performance requirements for the NEXT ion engine include a specific impulse of at least 4050 s at full power, and thruster efficiencies of greater than 0.63 and 0.42 at full and low power, respectively. The NEXT ion engine must further provide a 270 kg propellant throughput capability, which ultimately results in a 405 kg qualification throughput requirement.The NEXT propellant management system is required to deliver xenon flows to the ion engine with an uncertainty of ± 3%. Prov...

The High Power Electric Propulsion (HiPEP) Ion Thruster

“…As can be seen here, the specific impulse increases as expected monotonically with increasing power Thruster efficiencies greater than 65 % (NRA requirement) were demonstrated even for power levels as low as 6 kW as indicated in Fig. 7 32 This increase results in a slightly reduced discharge power requirement for a given beam current, thereby resulting in an improvement in thruster efficiency with increasing thruster power. Power levels up to nearly 40 kW are also illustrated in Fig.…”

Ion Engine Grid Gap Measurements

“…The neutralizer used for these tests was a NEXT laboratory model design, which is described in ref. 12. It will be shown later that the neutralizer had no discernable impact on the hot grid gap.…”

Single-String Integration Test Measurements of the NEXT Ion Engine Plume

“…11 Comparing the NEXT and NSTAR flatness parameters indicated that the NEXT EM1 ion engine beam flatness parameters were 45 to 85 percent higher than those of the NSTAR ion engine. 5,12 Higher flatness parameters apparently correspond directly with increased electron backstreaming limits, and are speculated to have contributed to increases in ion optics perveance and screen grid ion transparencies relative to those of the 30 cm ion optics on an NSTAR engine. The higher beam flatness parameters of the NEXT ion engine can also lead to reduced accelerator aperture enlargement near the grid center.…”

“…Details regarding the thruster design and performance have been published. [3][4][5][6] Integration of the EPT with the Aerojet manufactured breadboard PMS and the BEDD manufactured breadboard PPU into a "single-string" configuration was one of the major activities of Phase I. The objectives of this SingleString Integration Test (SSIT) were multi-fold: demonstrate operation of the thruster within specification of the NEXT throttle table 2 operating in concert with the breadboard PMS and PPU; verify full-functionality of the PMS and PPU; and, quantify other fault protection performance.…”