David H. Manzella

Benefits of Power and Propulsion Technology for a Piloted Electric Vehicle to an Asteroid

Abstract NASA’s goal for human spaceflight is to expand permanent human presence beyond low Earth orbit (LEO). NASA is identifying potential missions and technologies needed to achieve this goal. Mission options include crewed destinations to LEO and the International Space Station; high Earth orbit and geosynchronous orbit; cis-lunar space, lunar orbit, and the surface of the Moon; near-Earth objects; and the moons of Mars, Mars orbit, and the surface of Mars. NASA generated a series of design reference missions to drive out required functions and capabilities for these destinations, focusing first on a piloted mission to a near-Earth asteroid. One conclusion from this exercise was that a solar electric propulsion stage could reduce mission cost by reducing the required number of heavy lift launches and could increase mission reliability by providing a robust architecture for the long-duration crewed mission. Similarly, solar electric vehicles were identified as critical for missions to Mars, including orbiting Mars, landing on its surface, and visiting its moons. This paper describes the parameterized assessment of power and propulsion technologies for a piloted solar electric vehicle to a near-Earth asteroid. The objective of the assessment was to determine technology drivers to advance the stateof the art of electric propulsion systems for human exploration. Sensitivity analyses on the performance characteristics of the propulsion and power systems were done to determine potential system-level impacts of improved technology. Starting with a “reasonable vehicle configuration” bounded by an assumed launch date, we introduced technology improvements to determine the system-level benefits (if any) that those technologies might provide. The results of this assessment are discussed and recommendations for future work are described.

Feasibility of Large High-Powered Solar Electric Propulsion Vehicles: Issues and Solutions

Human exploration beyond low earth orbit will require the use of enabling technologies that are efficient, affordable, and reliable. Solar electric propulsion (SEP) has been proposed by NASA’s Human Exploration Framework Team (HEFT) as an option to achieve human exploration missions to Near Earth Objects (NEOs) because of its favorable mass efficiency as compared to traditional chemical systems. This paper describes the unique challenges and technology hurdles associated with developing a large high-power SEP vehicle. A subsystem level breakdown of factors contributing to the feasibility of SEP as a platform for future exploration missions to NEOs is presented including overall mission feasibility, trip time variables, propellant management issues, solar array power generation, array structure issues, and other areas that warrant investment in additional technology or engineering development.

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.

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.

Performance Evaluation of the NASA-300M 20 kW Hall Thruster

The performance of the NASA Glenn Research Center designed and fabricated 20 kW NASA-300M thruster was evaluated. Testing was performed at power levels between 2.5 and 20 kW with xenon and krypton propellants. Testing at all power levels and discharge voltage conditions indicated that the thruster operation was stable, no anomalous behavior or thermal limitations on thruster operation were observed. Xenon propellant testing at 20 kW indicated a peak total thrust efficiency of 67% and a peak total specific impulse of 2,920 s at discharge voltages of 500 and 600 V, respectively. Krypton propellant testing revealed peak total thrust efficiency of 63% and total specific impulse of 3,223 s at a discharge voltage of 600 V.

Development Status of the HiVHAC Hall Thruster

The High Voltage Hall Accelerator (HiVHAC) development program task, funded by the NASA Science Mission Directorates In-Space Propulsion Technology Program, is advancing the current state-of-the-art Hall thruste rs performance, life and cost. Its goal is to meet and/or exceed the requirements of Discovery class missions by developing a thruster that operates over a range of input powers from 0.3 to 3.5 kW, that can operate at specific impulses from 1,000 to 2,800 s, and that can proces s 300 kg of propellant while operating at full power. The HiVHAC program is currently building upon a history of design, analysis, fabrication, and test experience gained from a seri es of experimental investigations over the last several years. The latest design is the NASA- 103M.XL (eXtended Life) Hall thruster. This thruster incorporates design features enabling a projected lifetime in excess of 15,000 hours at a power level of 3.5 kW. A laboratory model of the NASA-103M.XL has demonstrated > 4,000 hours of wear testing at a dis charge voltage of 700 V. The next task of the HiVHAC program is to evolve this design into an engineering model thruster capable of demonstrating TRL-6 readiness. This paper will focus on the development status of the engineering model design.

Additional mission applications for NASA's 13.3-kW Ion propulsion system

NASAs Space Technology Mission Directorate has been recently developing critical technologies for high-power solar electric propulsion (SEP), including large deployable solar array structures and high-power electric propulsion components. An ion propulsion system based on these developments has been considered for many SEP technology demonstration missions, including the Asteroid Redirect Robotic Mission (ARRM) concept. These studies and the high-power SEP technology developments have generated excitement within NASA about the use of the ARRM ion propulsion system design for other types of potential missions. One application of interest is for Mars missions, especially with the types of orbiters now under consideration for flights in the early 2020s to replace the aging Mars Reconnaissance Orbiter. High-power SEP can deliver large payloads to Mars with many additional capabilities, including large orbital plane changes and round-trip missions, compared to chemically-propelled spacecraft. Another application for high-power SEP is for exo-planet observation missions, where a large starshade spacecraft would need to be repositioned with respect to its companion telescope relatively frequently and rapidly. SEP is an enabling technology for the ambitious science goals of these types of missions. This paper will discuss the benefits of high-power SEP for these concepts based on the STMD technologies now under development.

Development of a Hollow Cathode Assembly for the High Voltage Hall Accelerator

*† ‡ § The results of the H Igh Voltage Hall A Ccelerator ( HIVHA C) cathode d evelopment task are presented. The goal of th is task was to develop a cathode configuration that operate d in spot mode with minimal keeper power for the prescribed HIVHAC throttle table anode current levels and flow rates . Cathodes with equal cathode tube diameter but varied cathode orifice diameter, keeper configuration, and cathode orifice plate -keeper plate gap were tested. The nominal cathode configuration was that of the International Space Station (ISS ) plasma contactor cathode . The ca thode configuration that best satisfie d the HIVHAC throttle table has a cathode orifice diameter that is 40 % of the ISS plasma co ntactor cathode orifice diameter and a keeper configuration and cathode orifice plate -keeper plate gap identical to that of the ISS plasma contactor cathode . I. Introduction he H Igh Voltage Hall ACcelerator ( HIVHAC ) development program was selected under NASA’s In -Space Propulsion Technology Cycle 2 NASA Research Announcement (NRA) solicitation for “kilowatt solar electric prop ulsion system technology .” NASA Glenn Research Center (GRC) performed mission analysis comparing Hall thruster technology to NASA Evolutionary Xenon Thruster (NEXT) technology for deep space design reference missions (DSDRM) to Saturn and Neptune . The an alysis showed that if a spacecraft uses Hall thruster technology for earth orbit escape and interplanetary transfer, the spacecraft will obtain either a trip time reduction or a payload increase over a spacecraft employing a chemical propulsion system . Ba sed on these findings, NASA GRC proposed to develop a 6-8 kW Hall thruster that operates at a specific impulse of 22 00 -2800 seconds, uses xenon propellant, and has a thrust er efficiency of higher than 62 %. In May of 2003, HIVHAC was selected for award wit h NASA GRC leading partners Aerojet Redmond Rocket Center, the Jet Propulsion Laboratory (JPL), and the University of Michigan. 1 In 2004, the HIVHAC power requirement decreased to 0.3 -2.8 kW in order to expand the applicability of HIVHAC to Discovery clas s missions and New Frontiers class missions . 2

Radioisotope Electric Propulsion (REP): A Near-term Nuclear Propulsion System

Studies over the last decade have shown Radioisotope-based Nuclear Electric Propulsion (NEP) to be enhancing and, in some cases, enabling for many potential science missions. Also known as Radioisotope Electric Propulsion (REP), the technology offers the performance advantages of traditional fission-based NEP (i.e., high specific impulse (Isp) electric propulsion at large distances from the Sun), but with much smaller, affordable spacecraft. Future use of REP requires development of radioisotope power sources with system specific powers well above that of current systems. The U.S. Department of Energy (DOE) and NASA are currently developing the Advanced Stirling Radioisotope Generator (ASRG) Engineering Unit, which is culminating in flight qualification-level and extended life testing by the end of 2008. This advancement, along with recent work on small ion thrusters and lifetime extension technology for Hall thrusters, could enable missions using REP sometime during the next decade.