Engineering topics
Hill, M.
Publications and source records attributed to Hill, M..
Effect of Tube-Based X-Ray Microtomography Imaging on the Amino Acid and Amine Content of the Murchison CM2 Chondrite
X-ray and synchrotron X-ray micro-computed tomography (micro-CT) are increasingly being used for three dimensional reconnaissance imaging of chondrites and returned extraterrestrial material prior to detailed chemical and mineralogical analyses. Although micro-CT imaging is generally considered to be a non-destructive technique since silicate and metallic minerals in chondrites are not affected by X-ray exposures at the intensities and wavelengths typically used, there are concerns that the use of micro-CT could be detrimental to the organics in carbonaceous chondrites. We recently conducted a synchrotron micro-CT experiment on a powdered sample of the Murchison CM2 carbonaceous chondrite exposed to a monochromatic high energy (approximately 48 kiloelectronvolts) total X-ray radiation dose of approximately 1 kilogray (kGy) using the Advanced Photon Source beamline 13-BMD (13-Bending Magnet-D Beamline) at Argonne National Laboratory and found that there were no detectable changes in the amino acid abundances or enantiomeric compositions in the chondrite after exposure relative to a Murchison control sample that was not exposed. However, lower energy bremsstrahlung X-rays could interact more with amino acids and other lower molecular weight amines in meteorites. To test for this possibility, three separate micro-CT imaging experiments of the Murchison meteorite using the GE Phoenix v/tome/x s 240 kilovolt microfocus high resolution tungsten target X-ray tube instrument at the American Museum of Natural History (AMNH) were conducted and the amino acid abundances and enantiomeric compositions were determined. We also investigated the abundances of the C1-C5 amines in Murchison which were not analyzed in the first study.
Photogrammetry of the Map Instrument in a Cryogenic Vacuum Environment
MAP Instrument requirements dictated that the instruments Focal Plane Assembly (FPA) and Thermal Reflector System (TRS) maintain a high degree of structural integrity at operational temperatures (< 50K). To verify integrity at these extremes, an elaborate test fixture was constructed to provide a large cryogenic (< 20K) radiative environment and a mobile photogrammetry camera. This paper will discuss MAP's Instrument requirements, how those requirements were verified using photogrammetry, and the test setup used to provide the environment and camera movement needed to verify the instrument's requirements.
JPL's Multi-Mission Operations Strategy for the Next Decade
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A Multi-Mission Approach to Spacecraft Analysis
This paper describes the design of the JPL institutional Multi-Mission Spacecraft Analysis System (MSAS) and its initial adaptation to the Cassini mission.
Fluid management and its role in the future of Space Station
Technological challenges and suggested plans for meeting them pertaining to fluid management in the Space Station are discussed. A short overview is given of the major Space Station systems and operations which employ or rely on fluid management, followed by a description of the general system issues and challenges encountered in managing fluids in space. Examples of some current and near term activities directed toward providing the understanding and technologies necessary to overcome relevant problems are presented. Finally, suggested plans for similar but longer range research and development activities are offered. These plans emphasize the requirements and benefits of expanded in-space experiments, with the ultimate aim of using the Space Station as a facility for fluid management research and technology development efforts.
Low-thrust chemical propulsion system propellant expulsion and thermal conditioning study. Executive summary
Preferred techniques for providing abort pressurization and engine feed system net positive suction pressure (NPSP) for low thrust chemical propulsion systems (LTPS) were determined. A representative LTPS vehicle configuration is presented. Analysis tasks include: propellant heating analysis; pressurant requirements for abort propellant dump; and comparative analysis of pressurization techniques and thermal subcoolers.
Low-thrust chemical propulsion system propellant expulsion and thermal conditioning study
Thermal conditioning systems for satisfying engine net positive suction pressure (NPSP) requirements, and propellant expulsion systems for achieving propellant dump during a return-to-launch site (RTLS) abort were studied for LH2/LO2 and LCH4/LO2 upper stage propellant combinations. A state-of-the-art thermal conditioning system employing helium injection beneath the liquid surface shows the lowest weight penalty for LO2 and LCH4. A technology system incorporating a thermal subcooler (heat exchanger) for engine NPSP results in the lowest weight penalty for the LH2 tank. A preliminary design of two state-of-the-art and two new technology systems indicates a weight penalty difference too small to warrant development of a LH2 thermal subcooler. Analysis results showed that the LH2/LO2 propellant expulsion system is optimized for maximum dump line diameters, whereas the LCH4/LO2 system is optimized for minimum dump line diameter (LCH4) and maximum dump line diameter (LO2). The primary uncertainty is the accurate determination of two-phase flow rates through the dump system; experimentation is not recommended because this uncertainty is not considered significant.
Voyager 2 Saturn encounter attitude and articulation control experience
A description is given of the Voyager Attitude and Articulation Control System (AACS). The complex series of maneuvers required for Voyager 2 during the near encounter period to obtain fields and particle data, track the limb of Saturn during the earth occultation period, and reflect the RF beam off the Saturnian ring system are discussed. It is noted that some of these maneuvers involved rotating the spacecraft simultaneously about multiple axes while maintaining accurate pointing of the scan platform, a first for interplanetary missions. Also described are two anomalies experienced by the AACS during the near encounter period. The first was the significant roll attitude error that occurred shortly after all axis inertial control and that continued to grow until celestial reacquisition. The second was that the scan platform slewing in the azimuth axis stopped midway through the near encounter. These anomalies are analyzed, and their effect on future missions is assessed.
Voyager Saturn encounter attitude and articulation control experience
The Voyager attitude and articulation control system is designed for a three-axis stabilized spacecraft; it uses a biasable sun sensor and a Canopus Star Tracker (CST) for celestial control, as well as a dry inertial reference unit, comprised of three dual-axis dry gryos, for inertial control. A series of complex maneuvers was required during the first of two Voyager spacecraft encounters with Saturn (November 13, 1980); these maneuvers involved rotating the spacecraft simultaneously about two or three axes while maintaining accurate pointing of the scan platform. Titan and Saturn earth occulation experiments and a ring scattering experiment are described. Target motion compensation and the effects of celestial sensor interference are also considered. Failure of the CST, which required an extensive reevaluation of the star reference and attitude control mode strategy, is discussed. Results analyzed thus far show that the system performed with high accuracy, gathering data deeper into Saturn's atmosphere than on any previous planetary encounter.
Orbital refill of propulsion vehicle tankage
Techniques for orbital refueling of space based vehicles were developed and experimental programs to verify these techniques were identified. Orbital refueling operations were developed for two cryogenic orbital transfer vehicles (OTV's) and an Earth storable low thrust liquid propellant vehicle. Refueling operations were performed assuming an orbiter tanker for near term missions and an orbital depot. Analyses were conducted using liquid hydrogen and N2O4. The influence of a pressurization system and acquisition device on operations was also considered. Analyses showed that vehicle refill operations will be more difficult with a cryogen than with an earth storable. The major elements of a successful refill with cryogens include tank prechill and fill. Propellant quantities expended for tank prechill appear to to insignificant. Techniques were identified to avoid loss of liquid or excessive tank pressures during refill. It was determined that refill operations will be similar whether or not an orbiter tanker or orbital depot is available. Modeling analyses were performed for prechill and fill tests to be conducted assuming the Spacelab as a test bed, and a 1/10 scale model OTV (with LN2 as a test fluid) as an experimental package.