John R. Brophy

Status of the extended life test of the Deep Space 1 flight spare ion engine after 30,352 hours of operation

The extended life test (ELT) of the Deep Space 1 (DS1) spare flight ion thruster (FT2) was voluntarily terminated June 26th 2003. The test was started in Cotober of 1998, just prior to the launch of the DS1 spacecraft, with the primary purpose of determining the ultimate service life capability of the NASA 30-cm-ion thruster technology.

An overview of the Nuclear Electric Xenon Ion System (NEXIS) program

NASA is investigating high power, high specific impulse propulsion technologies that could enable ambitious flights such as multi-body rendezvous missions, outer planet orbiters and interstellar precursor missions. The requirements for these missions are much more demanding than those for state-of-the-art solar-powered ion propulsion applications. The purpose of the NEXIS program is to develop advanced ion thruster technologies that satisfy the requirements for high power, high specific impulse operation, high efficiency and long thruster life. The nominal design point for the NEXIS thruster is 20 kWe at a specific impulse of 7500 s with an efficiency over 78% and a xenon throughput capability of greater than 2000 kg. These performance and throughput goals will be achieved by applying a combination of advanced technologies including a large discharge chamber, erosion resistant carbon-carbon grids, an advanced reservoir hollow cathode and techniques for increasing propellant efficiency such as grid masking and accelerator grid aperture diameter tailoring. This paper provides an overview of the challenges associated with these requirements and how they are being addressed in the NEXIS program.

Performance Characterization and Vibration Testing of 30-cm Carbon-Carbon Ion Optics

Carbon-based ion optics have the potential to significantly increase the operable life and power ranges of ion thrusters because of reduced erosion rates compared to molybdenum optics. The development of 15-cm and larger diameter grids has encountered many problems, however, not the least of which is the ability to pass vibration testing. JPL has recently developed a new generation of 30-cm carbon-carbon ion optics in order to address these problems and demonstrate the viability of the technology. Perveance, electron backstreaming, and screen grid transparency data are presented for two sets of optics. Vibration testing was successfully performed on two different sets of ion optics with no damage and the results of those tests are compared to models of grid vibrational behavior. It will be shown that the vibration model is a conservative predictor of grid response and can accurately describe test results. There was no change in grid alignment as a result of vibration testing and a slight improvement, if any change at all, in optics performance.

Development and testing of carbon-based ion optics for 30-cm ion thrusters

Carbon-based ion optics have the potential to significantly increase the lifetime of state-of-the-art ion thrusters which use molybdenum optics because of the lower sputter yield and greater packing density of the carbon materials.

The NASA Electric Propulsion Program

Nearly all space missions require on-board propulsion systems and these systems typically have a major impact on spacecraft mass and cost. Electric propulsion systems offer major performance advantages over conventional chemical systems for many mission functions and the NASA Office of Space Access and Technology (OSAT) supports an extensive effort to develop the technology for high-performance, on-board electric propulsion system options to enhance and enable near- and far-term US space missions. This program includes research and development efforts on electrothermal, electrostatic, and electromagnetic propulsion system technologies to cover a wide range of potential applications. To maximize expectations of technology transfer, the program emphasizes strong interaction with the user community through a variety of cooperative and contracted approaches. This paper provides an overview of the OSAT electric propulsion program with an emphasis on recent progress and future directions.

Technology for a robotic Asteroid Redirect Mission and its extensibility to future human and robotic missions

Three aspects of the proposed Asteroid Redirect Mission (ARM) could be extended to provide greater capability for future NASA missions: higher-power versions of the baseline asteroid redirect vehicle, in-space resource utilization, and planetary defense. The baseline ARM vehicle assumes the use of a 50 kW beginning-of-life solar array which provides a maximum of 40 kW to the electric propulsion system. Launch dates in mid to late 2020 could provide the opportunity for the development and implementation of higher-power solar arrays and electric propulsion systems that are farther along the path to the 100-kW-class systems that could be used to support human missions to Mars. The ARM robotic vehicle conceptual design provides a straightforward approach to increasing the solar array power to ~100 kW for the first asteroid redirect mission. Transportation is also a major challenge for harvesting asteroids for the use of their material resources in space. ARM addresses this issue by selecting an asteroid that naturally returns close to Earth and then redirecting it into lunar orbit. Deriving propellants from asteroids is essential to a robust utilization of asteroid material resources. Two elements, magnesium and sulfur, abundantly available in common chondrite asteroids could be used as propellants in Hall thrusters and may be the key to asteroid mining. Finally, ARM has the potential to demonstrate two different planetary defense techniques: an enhanced gravity tractor, or an ion beam deflector. High-power solar electric propulsion (SEP) is needed for both techniques. Simple analyses highlight a clear choice between these options. To obtain the same force and total impulse applied to a potentially hazardous asteroid you can either develop higher power SEP systems for ion beam deflection or you can develop the capability to acquire hundreds of tons of mass from the asteroid for use with a lower power SEP system in an enhanced gravity tractor approach.

BMDO electric space-propulsion program

Electric propulsion (EP) applications being considered include: orbit insertion, orbit repositioning, station keeping, and elusive maneuvering. Typically, 1 to 5 kW are available for EP. A class of thrusters, the Hall-effect thrusters, is extensively researched, developed and flown by Russia. These thrusters, using xenon propellant, perform reliably, e.g., at 1.35 kW, 600 s specific impulse, 50 percent efficiency and greater than 2000 hr life. This specific impulse and efficiency combination is superior to the present arcjets for several Ballistic Missile Defense Organization (BMDO) applications. Three versions of the Hall thrusters are part of the experimental evaluation. Since todays goals are within reach of available thrusters and power sources, emphasis is being placed on such topics as: thruster lifetime, spacecraft interactions, electromagnetic interference, and erosion product deposition. Facilities in U.S. laboratories are being specially configured to achieve these goals.

Technology for a robotic asteroid redirect mission

In-space transportation technology is the key to unlocking the material resources of near-Earth asteroids for the benefit of human spaceflight activities beyond low-Earth orbit. High-power solar electric propulsion, with power levels of around 50 kW represents the most capable, affordable, near-term propulsion technology available and is enabling for the capture and retrieval of entire small near-Earth asteroids. Future technology advances, stimulated by the successful retrieval of the first asteroid, will likely include scaling to higher power levels, operation at higher specific impulse levels, and ultimately the use of asteroid-derived materials as propellant.

The status of ion propulsion development and implementation at JPL in 2003

The successful demonstration of ion propulsion on NASAs Deep Space 1 mission has stimulated substantial interest in the application of this technology to future solar system exploration missions.

Dawn ion propulsion system

The Dawn mission is designed to perform a scientific investigation of the main-belt asteroid (4) Ves…