Carl Hartsfield

Satellite propulsion spectral signature detection and analysis through Hall effect thruster plume and atmospheric modeling

Space Situational Awareness (SSA) is of utmost importance in todays congested and contested space environment. Satellites must perform orbital corrections for station keeping, devices like high efficiency electric propulsion systems such as a Hall effect thrusters (HETs) to accomplish this are on the rise. The health of this system is extremely important to ensure the satellite can maintain proper position and perform its intended mission. Electron temperature is a commonly used diagnostic to determine the efficiency of a hall thruster. Recent papers have coordinated near infrared (NIR) spectral measurements of emission lines in xenon and krypton to electron temperature measurements. Ground based observations of these spectral lines could allow the health of the thruster to be determined while the satellite is in operation. Another issue worth considering is the availability of SSA assets for ground-based observations. The current SSA architecture is limited and task saturated. If smaller telescopes, like those at universities, could successfully detect these signatures they could augment data collection for the SSA network. To facilitate this, precise atmospheric modeling must be used to pull out the signature. Within the atmosphere, the NIR has a higher transmission ratio and typical HET propellants are approximately 3x the intensity in the NIR versus the visible spectrum making it ideal for ground based observations. The proposed research will focus on developing a model to determine xenon and krypton signatures through the atmosphere and estimate the efficacy through ground-based observations. The model will take power modes, orbit geometries, and satellite altitudes into consideration and be correlated with lab and field observations.

Design and Characterization of a Space-Based Imaging Experiment Computer Unit

AbstractThe space-based chromotomographic experiment (CTEx), a hyperspectral imager, is currently in development at the Air Force Institute of Technology. This paper details an investigation of hermetic enclosures to house commercial off-the-shelf (COTS) components. These enclosures will enable the use of electronics in space which may not be available in a space-qualified form for years and reduce cost/schedule constraints. This activity produced an experimentally validated thermal mathematical model supporting further trade-space refinement and operational planning aspects for this device. Results support the transition of this next-generation technology from the laboratory to a fully-realized, space-readied platform uniquely capable of generating hyperspectral data at high spectral and temporal resolutions.

Pseudo Linear Hall Effect Thruster Characterization Through Potential, Magnetic, and Optical Measurements

Electric propulsion systems are a more mass efficient method for providing a change in velocity, ΔV, to on-orbit spacecraft, than their chemical counterparts. In comparison, electric systems generally have a much higher specific impulse, Isp, than chemical systems. One option within the realm of electric propulsion is Hall Effect Thrusters, which have moderately high specific impulse values. From their advent in the 1960s, Hall Effect Thrusters have been used for orbit station keeping, attitude control, and orbit transfer. Although the discharge cavity is conventionally circular, pseudo-linear or racetrack shaped cavities have been developed. Even though Hall thrusters have decades of flight heritage, there are still many plasma behavioral characteristics which are still unknown. Multiple non-intrusive measurement techniques were used to investigate plasma behavior both in the plume and in the channel of a pseudo linear Hall thruster. Through the visible emissions captured by a high-speed camera, breathing mode characteristics were induced and analyzed. Spoke structures were observed in only certain parts of the thruster channel. Additionally, the plume divergence was characterized by use of a Faraday probe along two axes of the thruster, indicating significantly different “keep out” regions for potential thruster use on spacecraft. Also, an irregularity was observed in the channel of the pseudo-linear thruster, which potentially could affect the lifespan of the thruster.

Satellite propulsion spectral signature detection and analysis

Space Situational Awareness (SSA) is of utmost importance in todays space dependent, congested and contested environment. The health of a propulsion system is vital to ensure proper function and thus proper mission placement. Electric propulsion is gaining popularity for satellite propulsion systems due to higher efficiencies, specific impulse, and the savings it offers in both spacecraft mass and launch costs. Electron temperature is a commonly used diagnostic to determine the efficiency of a Hall thruster. Recent papers have coordinated near infrared (NIR) spectral measurements of ionization lines in xenon and krypton to electron temperature measurements. This research will characterize NIR plume emissions for a 600 Watt Hall thruster using both xenon and krypton propellants for a variety of observation angles and operating power levels. By determining spectral differences when altering these variables, it would be possible to identify angle, power level, and propellant in order to provide information on electron temperature and thus efficiency. Although they have a high specific impulse, electric propulsion systems provide lower thrust than chemical alternatives. This means that the firing times needed for spacecraft maneuvers can be on the order of hours to months. This provides an opportunity for this characterization to not only be put to use in chamber experiments but on-orbit as well. Ground-based observations of these spectral lines would allow for identification of the type of thruster as well as the health of the system while the satellite is in operation on-orbit. The current SSA architecture is limited and task saturated. If smaller telescopes, like those at universities, could successfully detect these signatures they could augment data collection for the SSA network. To facilitate data collection, precise atmospheric modeling must be used to identify the signature. Within the atmosphere, the NIR has a higher transmission rate and typical HET propellants are approximately 3x the intensity in the NIR versus the visible spectrum making it ideal for ground based observations. This research will combine emission measurements with atmospheric and plume models to develop a single end-to-end model that will determine xenon and krypton signatures through the atmosphere, discernable differences in power level and viewing angle of Hall thruster systems, and estimate the efficacy through ground-based observations.

Optimized Dual-Expander Aerospike Nozzle Upper Stage Rocket Engine

The Air Force Institute of Technology (AFIT) is researching the cryogenic DualExpander Aerospike Nozzle (DEAN) upper stage rocket engine. The objectives for the DEAN design are 50,000 pounds-force (222 kilonewtons) vacuum thrust, 464 seconds of vacuum specific impulse and a thrust-to-weight ratio of 106.5. Previous work at AFIT focused on first developing a feasible closed design model and secondly expanding the model to support parametric trade studies and optimization. The current model utilizes NASA’s Numerical Propulsion System Simulation (NPSS) and Phoenix Integration’s ModelCenter. Current work expands the NPSS and ModelCenter DEAN model to estimate engine weight and optimize thrust-to-weight ratio. Furthermore, the DEAN model has been enhanced to allow further exploration of the solution space while offering the opportunity to identify critical technologies/parameters.