This dissertation presents research aimed at extending the efficient operation of 1600 s specific impulse Hall thruster technology to the 2000 to 3000 s range. Motivated by previous industry efforts and mission studies, the aim of this research was to develop and characterize xenon Hall thrusters capable of both high-specific impulse and high-efficiency operation. During the development phase, the laboratory-model NASA 173M Hall thrusters were designed and their performance and plasma characteristics were evaluated. Experiments with the NASA-173M version 1 (v1) validated the plasma lens magnetic field design. Experiments with the NASA 173M version 2 (v2) showed there was a minimum current density and optimum magnetic field topography at which efficiency monotonically increased with voltage. Comparison of the thrusters showed that efficiency can be optimized for specific impulse by varying the plasma lens. During the characterization phase, additional plasma properties of the NASA 173Mv2 were measured and a performance model was derived. Results from the model and experimental data showed how efficient operation at high-specific impulse was enabled through regulation of the electron current with the magnetic field. The electron Hall parameter was approximately constant with voltage, which confirmed efficient operation can be realized only over a limited range of Hall parameters.

/pdf/development-and-characterization-of-high-efficiency-high-50q4vw4pje.pdf

Development and Characterization of High-Efficiency, High-Specific Impulse Xenon Hall Thrusters

HE overriding goal of advanced space propulsion is to reduce the costs of doing space missions, and to enable totally new types of missions that basically could not be performed (even at essentially unlimited cost) with existing technology. For example, with Earth-launch costs on the order of $10,000 per kilogram (comparable to the current cost of gold!) of delivered payload, one important application of advanced propulsion is to reduce thecostofaccessto space(andtransportation oncein space), both in the initial Earth-launch vehicle and then in the in-space vehicles, by reducing the total mass (most of which is propellant) that must be launched from Earth. This can be achieved by either developing more efe cient, higher-performance (i.e., higher specie c impulse Isp/ propulsion technologies, or by reducing the propellant requirements by reducing dry mass, mission velocity 1V, and so on. (Note however that launch cost is strongly driven by launch frequency; 1 thus, some advanced propulsion concepts attempt to both improve performance and increase launch rate.) A second goal of advanced propulsion is the ability to perform previously “ impossible” missions. An example of an impossible mission is attempting an interstellar mission using chemical propulsion. No matter how large the rocket, no matter how many stages it has, you simply cannot achieve the speeds (typically at least 10%of the speed of light) required for a practical interstellar mission using a chemical propulsion system. More generally, it is not practical to performaspace mission wherethe mission 1V isgreater than afew (e.g., two to three) times the propulsion system’ s exhaust velocity Vexhaust or, equivalently, Isp. Ultimately,theperformanceofanyrocketislimitedbytheRocket

Advanced Space Propulsion for the 21st Century

Low perturbation interrogation of the internal and near -field plasma structure of a Hall thruster using a high -speed probe positioning system.

: The University of Michigan and United States Air Force Research Laboratory have jointly developed a 5 kW class Hall effect thruster. This thruster was developed to investigate, with a variety of diagnostics, a thruster similar to that specified by IHPRPT goals. The configuration of this thruster is adjustable so that diagnostic access to the interior of the thruster can be provided as necessary, and to allow for the exploration of various thruster geometries. At nominal conditions, the thruster was designed to operate at 5 kW with a predicted specific impulse of 2200 s. The actual operating parameters at 5 kW were 2326 s specific impulse, with 246 mN of thrust at an efficiency of 57%. These conditions are comparable to those of thrusters under commercial development, making the information learned from the study of this thruster applicable to the understanding of its commercial counterparts.

/pdf/performance-characteristics-of-a-5-kw-laboratory-hall-qrova7v8wd.pdf

Performance characteristics of a 5 kW laboratory hall thruster

Anexperimentalapparatususingtriplelangmuirprobeswasdesignedtoobtainelectrontemperatureanddensity in theplume of a laboratory-model pulsed plasma thruster (PPT)operating at discharge energy levels of 5, 20, and 40 J. Electron temperature and density were obtained on two planes parallel and perpendicular to the thruster electrodes passing through the thruster’ s centerline. Measurements were obtained for radial distances of 6, 10, 12, 14,16,18,and20cmandforpolaranglesof10,20,30,and45degwithrespectto thecenteroftheTee on ® propellant face.Plumepropertiesshowlargeangularvariationontheperpendiculartotheelectrodesplanebutsmallvariation on the parallel plane cone rming the asymmetry of the PPT plume. Electron density and temperature decrease with increasing radial distance from the Tee on surface. The average maximum temperature is between 2 and 4 eV for all discharge energy levels considered. The average maximum electron density is 1 6 £ 10 20 , 1 6 £ 10 21 , and 1 8 £ 10 21 m i 3 for the 5-, 20-, and 40-J discharge. The time-average electron density increases with increasing discharge energy and is in the range between 10 19 and 2 £ 10 20 m i 3 for 5 J, 3 £ 10 19 and 10 21 m i 3 for 20 J, and 5 £ 10 19 and 1 4 £ 10 21 m i 3 for 40 J. Nomenclature An = area of probe n 1;2;3 ds = probe sheath thickness e

Langmuir Probe Measurements in the Plume of a Pulsed Plasma Thruster

: An overview of current electric propulsion research and development efforts within the United States Air Force is presented. The Air Force supports electric propulsion primarily through the Air Force Office of Scientific Research (AFOSR), the Air Force Research Laboratory (AFRL) and the AFOSR European Office of Aerospace Research and Development (EOARD). Overall direction for the programs comes from Air Force Space Command (AFSPC), with AFRL mission analysis used to define specific technological advances needed to meet AFSPC priorities. AFOSR funds basic research in electric propulsion throughout the country in both academia and industry. The AFRL Propulsion Directorate conducts electric propulsion efforts in basic research, engineering development, and space flight experiments. EOARD supports research at foreign laboratories that feeds directly into AFSR and AFRL research programs. Current research efforts fall into 3 main categories defined loosely by the thruster power level. All three agencies are conducting research at the low-power regime (P 30 kW) is realizing increased emphasis.

Overview of the USAF Electric Propulsion Program

: We report the first observation of a two-photon laser-induced fluorescence (LIF) technique in an arcjet plume. Ground state hydrogen atoms are detected with high spatial resolution near the thruster nozzle exit. Number density, axial and radial velocity, and translational temperature distributions are obtained in the expansion plume of a 1 kW arcjet operating on hydrogen propellant. Comparison of the ground state properties with previously measured excited state hydrogen data and recent computational data is discussed.

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA436728&Location=U2&doc=GetTRDoc.pdf

Laser induced fluorescence of ground state hydrogen atoms at nozzle exit of an arcjet thruster

: All overview of current electric propulsion research and development efforts within the United States Air Force is presented. The Air Force supports electric propulsion primarily through the Air Force Office of Scientific Research (AFOSR), the Air Force Research Laboratory (AFRL) and the AFOSR European Office of Aerospace Research and Development (BOARD). Overall direction for the programs comes from Air Force Space Command (AFSPC), with AFRL mission analysis used to define specific technological advances needed to meet AFSPC mission priorities. AFOSR funds basic research in electric propulsion throughout the country in both academia and industry. The AFRL Propulsion Directorate conducts electric propulsion efforts in basic research, engineering development, and space flight experiments. BOARD supports research at foreign laboratories that feeds directly into AFOSR and AFRL research programs. Current research efforts fall into 3 main categories defined loosely by the thruster power level. All three agencies are conducting research at the low-power regime (P 30 kW) is realizing increased emphasis.

/pdf/the-usaf-electric-propulsion-research-program-1hlm0ggiji.pdf

The USAF Electric Propulsion Research Program

Performance testing of a resistojet thruster for small satellite applications

Spacecraft thrusters capable of dual-mode operation, and a method of applying propulsion to a spacecraft using a dual-mode thruster are provided. In one embodiment, the thrusters of the current invention can operate as a chemical motor to provide high thrust and low propellant exhaust velocity to achieve fast maneuverability, or as an electric propulsion thruster to provide low thrust and high exhaust velocity to perform maneuvers with a minimal amount of propellant.

Ronald A. Spores

Papers

Overview of the USAF Electric Propulsion Program

Laser induced fluorescence of ground state hydrogen atoms at nozzle exit of an arcjet thruster

The USAF Electric Propulsion Research Program

Performance testing of a resistojet thruster for small satellite applications

Dual-mode chemical-electric thrusters for spacecraft