Vincent K. Rawlin

NEXT: NASA's Evolutionary Xenon Thruster

NASA’s Glenn Research Center has been selected to lead development of NASA’s Evolutionary Xenon Thruster (NEXT) system. The central feature of the NEXT system is an electric propulsion thruster (EPT) that inherits the knowledge gained through the NSTAR thruster that successfully propelled the Deep Space 1 to asteroid Braille and comet Borrelly, while significantly increasing the thruster power level and making improvements in performance parameters associated with NSTAR. The EPT concept under development has a 40 cm beam diameter, twice the effective area of the Deep-Space 1 thruster, while maintaining a relatively-small volume. It incorporates mechanical features and operating conditions to maximize the design heritage established by the flight NSTAR 30 cm engine, while incorporating new technology where warranted to extend the power and throughput capability.

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 Projects in U.S.: Space Electric Rocket Test I to Deep Space 1

The historical background and characteristics of the experimental flights of ion propulsion systems and the major ground-based technology demonstrations are reviewed. The results of the first successful ion engine flight in 1964, Space Electric Rocket Test (SERT) I, which demonstrated ion beam neutralization, are discussed along with the extended operation of SERT II starting in 1970. These results together with the technologies employed on the early cesium engine flights, the applications technology satellite series, and the ground-test demonstrations, have provided the evolutionary path for the development of xenon ion thruster component technologies, control systems, and power circuit implementations. In the 1997-1999 period, the communication satellite flights using ion engine systems and the Deep Space 1 flight confirmed that these auxiliary and primary propulsion systems have advanced to a high level of flight readiness.

Ion Thruster Development Trends and Status in the United States

The current interest in ion thrusters for near-Earth and deep-space missions has occurred because of long-term development efforts yielding an understanding of the physical phenomena involved in thruster operation and hardware that is suited to a wide range of missions. Features of state-of-the-art thrusters are described in terms of the various physical processes that occur within them. Tradeoffs that must be considered to arrive at thruster designs suited to commercialization are discussed.

NSTAR flight thruster qualification testing

Deep Space 1 is a technology demonstration mission scheduled to be launched in October 1998. One of those technologies is the NSTAR 30 cm diameter xenon ion thruster which will provide the primary propulsion. Three Flight-design thrusters were designed and built by Hughes Electron Dynamics Division, with assistance from NASAs Lewis Research Center. The first thruster was a Pathfinder to finalize the fabrication and assembly procedures for the other thrusters. Two flight-worthy thrusters were then fabricated and tested to Protoflight Qualification levels at NASAs Lewis Research Center and Jet Propulsion Laboratory. Each thruster was performance tested before and after Vibration Tests, integrated with different flight power processors and digital control interface units, and underwent Thermal Vacuum Tests with engine starts from -97 °C. Performance tests included neutralizer, discharge chamber, and ion optics characterizations as well as measurements of thruster efficiency over the full 0.5 to 2.3 kW power throttle range. The performance, at both component and thruster levels, was as expected and found to be quite repeatable with negligible dispersion between thrusters. After final functional tests, one thruster was installed on the DS 1 spacecraft while the other was set aside as a flight spare.

Results of an On-Going Long Duration Ground Test of the DS1 Flight Spare Engine

Ground testing of the DS1 night spare thruster (FT2) is presently being conducted. To date, the thruster has accumulated over 4500 hours of operation. Comparison of FT2 with the performance of the engineering model thruster 2 (EMT2) during the 8.2 khr test shows a transient, lasting for about 3000 hours, during which the discharge chamber efficiency decreases for both thrusters. The flow rates are 2% lower for FT2 than for EMT2 and the discharge chamber performance is 4.5% lower for FT2 during the transient. Sensitivity data obtained during the test show that the lower flow rate accounts for about half of the observed difference. After the initial transients decay, the performance of both thrusters is comparable with the exception of the electron backstreaming margin--which is 6 V lower for FT2.

NASA 30 Cm Ion Thruster Development Status

A 30 cm diameter xenon ion thruster is under development at NASA to provide an ion propulsion option for missions of national interest and it is an element of the NASA Solar Electric Propulsion Technology Applications Readiness (NSTAR) program established to validate ion propulsion for space flight applications. The thruster has been developed to an engineering model level and it incorporates innovations in design, materials, and fabrication techniques compared to those employed to conventional ion thrusters. The performance of both functional and engineering model thrusters has been assessed including thrust stand measurements, over an input power range of 0.5-2.3 kW. Attributes of the engineering model thruster include an overall mass of 6.4 kg, and an efficiency of 65 percent and thrust of 93 mN at 2.3 kW input power. This paper discusses the design, performance, and lifetime expectations of the functional and engineering model thrusters under development at NASA.

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.

Performance characteristics of the deep space 1 flight spare ion thruster long duration test, the first 21,300 hours of operation

A long duration test of the DSl flight spare ion thruster (FT2) is presently being conducted at the Jet Propulsion Laboratory. To, date the thruster has accumulated over 23,500 hours of operation, and 190 kg of Xenon propellant, over 230% of the initial design life. The primary objectives of the test include the processing of 200 kg of Xenon propellant, the identification of unknown failure modes, the characterization and drivers of these failure modes, and to measure performance degradation as the thruster wears. The test is fitted with an extensive array of diagnostics to measure engine wear and performance degradation. To date the most notable erosion processes include severe discharge cathode keeper erosion, accelerator grid erosion, reduction in electrical isolation of the neutralizer assembly, and deposit formation within the neutralizer orifice, reducing margin from plume mode. Over the past 23,500 hours of operation, performance degradation has been minimal, and it is anticipated that the above erosion processes will not preclude the thruster from processing over 200 kg of Xenon.

Performance of 10-kW class xenon ion thrusters

Presented are performance data for laboratory and engineering model 30 cm-diameter ion thrusters operated with xenon propellant over a range of input power levels from approximately 2 to 20 kW. Also presented are preliminary performance results obtained from laboratory model 50 cm-diameter cusp- and divergent-field ion thrusters operating with both 30 cm- amd 50 cm-diameter ion optics up to a 20 kW input power. These data include values of discharge chamber propellant and power efficiencies, as well as values of specific impulse, thruster efficiency, thrust and power. The operation of the 30 cm- and 50 cm-diameter ion optics are also discussed.