Luis R. Pinero

Development of an Ion Thruster and Power Processor for New Millennium's Deep Space 1 Mission

James S. Sovey, John A. Hamley, Thomas W. Haag, Michael J. Patterson, Eric J. Pencil,Todd T. Peterson, Luis R. Pinero, John L. Power, Vincent K. Rawlin, and Charles J. SarmientoNASA Lewis Research Center, Cleveland, OhioJohn R. Anderson, Raymond A. Becker, John R. Brophy, and James E. PolkJet Propulsion Laboratory, Pasadena, CaliforniaGerald Benson, Thomas A. Bond, G. I. Cardwell, Jon A. Christensen, Kenneth J. Freick,David J. Hamel, Stephen L. Hart, John McDowell, Kirk A. Norenberg, T. Keith Phelps,Ezequiel Solis, and Harold YostHughes Electron Dynamics Division, Torrance, CaliforniaMichael MatrangaSpectrum Astro Incorporated, Gilbert, ArizonaPrepared for the33rd Joint Propulsion Conference and Exhibitcosponsored by AIAA, ASME, SAE, and ASEESeattle, Washington, July 6-9, 1997National Aeronautics andSpace AdministrationLewis Research Center

Ion propulsion development activities at the NASA Glenn Research Center

The NASA Glenn Research Center (GRC) ion propulsion program addresses the need for high specific impulse ion propulsion systems and technology across a broad range of mission applications and power levels. Development areas include high-throughput NSTAR derivative engine and power processing technology, lightweight high-efficiency sub-kilowatt ion propulsion, micro-ion propulsion concepts, engine and component technologies for highpower (30 kW class) ion engines, and fundamentals. NASA GRC is also involved in two highly focussed activities: development of 5/10-kW class next-generation ion propulsion system technology, and development of high-specific impulse (> 10,000 seconds) ion propulsion technology applicable to deep-space and interstellar-precursor missions.

In-Space Propulsion High Voltage Hall Accelerator Development Project Overview

NASA’s Science Mission Directorate In-Space Propulsion Technology Project is funding the development of a high specific impulse long life Hall thruster. The goal of the high voltage Hall accelerator (HiVHAc) project is to develop a flight-like, engineering model (EM) Hall thruster that can meet future NASA science mission requirements. These requirements are met by a thruster that operates over an input power range from 0.3 to 3.5 kW, attains specific impulses from 1,000 to 2,700 seconds, and processes at least 300 kg of xenon propellant at full power. To demonstrate the HiVHAc project goal, two laboratory thrusters have been built and tested. The latest laboratory thruster, the NASA-103M.XL, incorporated a life-extending discharge channel replacement innovation and has been operated for approximately 5,000 hours at a discharge voltage of 700 volts. In 2007, NASA Glenn Research Center teamed with Aerojet to design and manufacture a flight-like HiVHAc EM thruster which incorporated this life-extending channel replacement innovation. The EM thruster was designed to withstand the structural and thermal loads encountered during NASA science missions and to attain performance and lifetime levels consistent with NASA missions. Aerojet and NASA Glenn Research Center have completed the EM thruster design, structural and thermal analysis, fabrication of thruster components, and have assembled and extensively tested one EMl thruster. Performance and thermal characterization of the engineering model thruster has been performed for discharge power levels up to 3.5 kW. The results indicate discharge efficiencies up to of 63% and discharge specific impulse up to 2,930 seconds. In addition to the thruster development, the HiVHAc project is leveraging power processing unit and xenon flow system developments sponsored by other projects but that can apply directly to a HiVHAc system. The goal is to advance the technology readiness level of a HiVHAc propulsion system to 6.

NEXT Single String Integration Test Results

As a critical part of NASAs Evolutionary Xenon Thruster (NEXT) test validation process, a single string integration test was performed on the NEXT ion propulsion system. The objectives of this test were to verify that an integrated system of major NEXT ion propulsion system elements meets project requirements, to demonstrate that the integrated system is functional across the entire power processor and xenon propellant management system input ranges, and to demonstrate to potential users that the NEXT propulsion system is ready for transition to flight. Propulsion system elements included in this system integration test were an engineering model ion thruster, an engineering model propellant management system, an engineering model power processor unit, and a digital control interface unit simulator that acted as a test console. Project requirements that were verified during this system integration test included individual element requirements ; integrated system requirements, and fault handling. This paper will present the results of these tests, which include: integrated ion propulsion system demonstrations of performance, functionality and fault handling; a thruster re-performance acceptance test to establish baseline performance: a risk-reduction PMS-thruster integration test: and propellant management system calibration checks.

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

Near-Term High Power Ion Propulsion Options for Earth- Orbital Applications

There is a convergence in requirements among various elements of the U.S. government and commercial industry relative to high-power electric propulsion systems for Earth- orbital applications, and in the advancement of high power lightweight photovoltaic array technologies. Some of these requirements and capabilities align well with NASA electric propulsion technologies, and specifically ion propulsion. NASAs investment strategy in electric propulsion over the last decade has established the ground work for the development of a number of high power ion thruster concepts, which have evolved to various levels of technology readiness. Some of these concepts could provide the basis for the development of flight ion propulsion systems consistent with Earth-orbital applications needs. This could allow for the fielding of high power systems (20 - 80 kW) with single thruster power handling capability of up to 20 kW and higher, and do so within a decade. This paper identifies and examines a number of thruster options. Assessments of technology readiness level, development roadmaps, technology challenges, and schedule are provided.

Performance of the NEXT Engineering Model Power Processing Unit

The NASA s Evolutionary Xenon Thruster (NEXT) project is developing an advanced ion propulsion system for future NASA missions for solar system exploration. An engineering model (EM) power processing unit (PPU) for the NEXT project was designed and fabricated by L-3 Communications under contract with NASA Glenn Research Center (GRC). This modular PPU is capable of processing up from 0.5 to 7.0 kW of output power for the NEXT ion thruster. Its design includes many significant improvements for better performance over the state-of-the-art PPU. The most significant difference is the beam supply which is comprised of six modules and capable of very efficient operation through a wide voltage range because of innovative features like dual controls, module addressing, and a high current mode. The low voltage power supplies are based on elements of the previously validated NASA Solar Electric Propulsion Technology Application Readiness (NSTAR) PPU. The highly modular construction of the PPU resulted in improved manufacturability, simpler scalability, and lower cost. This paper describes the design of the EM PPU and the results of the bench-top performance tests.

Performance and Environmental Test Results of the High Voltage Hall Accelerator Engineering Development Unit

NASA Science Mission Directorates In-Space Propulsion Technology Program is sponsoring the development of a 3.5 kW-class engineering development unit Hall thruster for implementation in NASA science and exploration missions. NASA Glenn and Aerojet are developing a high fidelity high voltage Hall accelerator that can achieve specific impulse magnitudes greater than 2,700 seconds and xenon throughput capability in excess of 300 kilograms. Performance, plume mappings, thermal characterization, and vibration tests of the high voltage Hall accelerator engineering development unit have been performed. Performance test results indicated that at 3.9 kW the thruster achieved a total thrust efficiency and specific impulse of 58%, and 2,700 sec, respectively. Thermal characterization tests indicated that the thruster component temperatures were within the prescribed material maximum operating temperature limits during full power thruster operation. Finally, thruster vibration tests indicated that the thruster survived the 3-axes qualification full-level random vibration test series. Pre and post-vibration test performance mappings indicated almost identical thruster performance. Finally, an update on the development progress of a power processing unit and a xenon feed system is provided.

Overview of the Development of a Low Cost High Voltage Hall Accelerator Propulsion System for NASA Science Missions

NASA’s Science Mission Directorate In-Space Propulsion Technology Program is funding NASA Glenn Research Center (GRC) to develop a high specific impulse, long-life, low-cost high voltage Hall accelerator (HiVHAc) engineering model (EM) Hall effect thruster. NASA GRC and Aerojet have completed the fabrication and extensive testing of a HiVHAc EM thruster that incorporates a discharge channel replacement mechanism as a means of achieving long-life. HiVHAc EM performance characterization indicated that the design met and exceeded desired performance levels. A new throttle table that includes high thrust-to-power operation has improved the thruster’s performance for some NASA science missions. However, testing also revealed that thermal, magnetic circuit saturation, and channel replacement mechanism issues and challenges exist. As a result, NASA GRC and Aerojet initiated and completed design changes to the EM thruster to alleviate encountered issues and challenges. In addition, the HiVHAc project is leveraging power processing unit (PPU) developments by Aerojet and by NASA’s Small Business Initiative Research Program. This includes evaluating performance of a wide-output range brassboard PPU that can process input voltages between 80 and 160 volts and is capable of output voltages between 200 and 700 V. Finally, the HiVHAc project has leveraged xenon feed system development by the Science Mission Directorate’s In Space Propulsion Technology Program. The HiVHAc project and Air Force Research Laboratory are funding the development of the next generation of light-weight, low-power consumption, and small-footprint xenon feed system. The unit, designated xenon flow control module, is manufactured by VACCO and will be delivered to NASA GRC in September 2011.

NEXT Thruster Component Verification Testing

Abstract Component testing is a critical part of thruster life validation activities under NASA’s Evolutionary Xenon Thruster (NEXT) project testing. The high voltage propellant isolators were selected for design verification testing. Even though they are based on a heritage design, design changes were made because the isolators will be operated under different environmental conditions including temperature, voltage, and pressure. The life test of two NEXT isolators was therefore initiated and has accumulated more than 10,000 hr of operation. Measurements to date indicate only a negligibly small increase in leakage current. The cathode heaters were also selected for verification testing. The technology to fabricate these heaters, developed for the International Space Station plasma contactor hollow cathode assembly, was transferred to Aerojet for the fabrication of the NEXT prototype model ion thrusters. Testing the contractor-fabricated heaters is necessary to validate fabrication processes for high reliability heaters. This paper documents the status of the propellant isolator and cathode heater tests.