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At least 1,027 records · Page 57
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Problems with aging wiring in Naval aircraft

The Navy is experiencing a severe aircraft electrical wiring maintenance problem as a result of the extensive use of an aromatic polyimide insulation that is deteriorating at a rate that was unexpected when this wire was initially selected. This problem has significantly affected readiness, reliability, and safety and has greatly increased the cost of ownership of Naval aircraft. Failures in wire harnesses have exhibited arcing and burning that will propagate drastically, to the interruption of many electrical circuits from a fault initiated by the failure of deteriorating wires. There is an urgent need for a capability to schedule aircraft rewiring in an orderly manner with a logically derived determination of which aircraft have aged to the point of absolute necessity. Excessive maintenance was demonstrated to result from the accelerated aging due to the parameters of moisture, temperature, and strain that exist in the Naval Aircraft environment. Laboratory studies have demonstrated that MIL-W-81381 wire insulation when aged at high humidities followed the classical Arrhenius thermal aging relationship. In an extension of the project a multifactor formula was developed that is now capable of predicting life under varying conditions of these service parameters. An automated test system has also been developed to analyze the degree of deterioration that has occurred in wires taken from an aircraft in order to obtain an assessment of remaining life. Since it is both physically and financially impossible to replace the wiring in all the Navy's aircraft at once, this system will permit expedient scheduling so that those aircraft that are most probable to have wiring failure problems can be overhauled first.

Campbell, Frank J.↗
NASA NTRS1985

Exercise hyperthermia as a factor limiting physical performance - Temperature effect on muscle metabolism

The effect of trunk cooling on the muscle contents of ATP, ADP, AMP, creatine phosphate (CrP), and creatine, as well as of glycogen, some glycolytic intermediates, pyruvate, and lactate were assessed in 11 fasted dogs exercised at 20 C on treadmill to exhaustion. Without cooling, dogs were able to run 57 min, and their rectal (Tre) and muscle (Tm) temperatures increased to 41.8 and 43.0 C, respectively. Cooling with ice packs prolonged the ability to run by 45 percent, and resulted in lower Tre (by 1.1 C) and Tm (by 1.2 C). Depletion of muscle content of total high-energy phosphates (ATP + CrP) and glycogen, and increases in contents of AMP, pyruvate, and lactate were lower in cooled dogs than in non-cooled dogs. The muscle content of lactiate correlated positively with TM. These results indicate that hypothermia accelerates glycolysis, and shifts the equilibrium between high- and low-energy phosphates in favor of the latter. The adverse effect of hypothermia on muscle metabolism may be relevant to the limitation of endurance.

Kozlowski, S.↗
NASA NTRS1991

Characterization of a 5-eV neutral atomic oxygen beam facility

An experimental effort to characterize an existing 5-eV neutral atomic oxygen beam facility being developed at Princeton Plasma Physics Laboratory is described. This characterization effort includes atomic oxygen flux and flux distribution measurements using a catalytic probe, energy determination using a commercially designed quadrupole mass spectrometer (QMS), and the exposure of oxygen-sensitive materials in this beam facility. Also, comparisons were drawn between the reaction efficiencies of materials exposed in plasma ashers, and the reaction efficiencies previously estimated from space flight experiments. The results of this study show that the beam facility is capable of producing a directional beam of neutral atomic oxygen atoms with the needed flux and energy to simulate low Earth orbit (LEO) conditions for real time accelerated testing. The flux distribution in this facility is uniform to +/- 6 percent of the peak flux over a beam diameter of 6 cm.

Vaughn, J. A.↗
NASA NTRS1982

Response of rat body composition to simultaneous exercise and centrifugation at 3.14g

A study is described calling into question the hypothesis that an increased physical load during chronic centrifugation contributes to the body composition changes observed in centrifuged rats. Considering fat-free and fat-free dry masses of the total body and carcass, it is seen that centrifugation combined with either wheel running or restraint reduced these masses to approximately 85% of the respective 1-g values, that is, the same result with either sedentary rats or rats running several hundred meters per day. It is pointed out that if an effect of a centrifugation-induced load is present but hidden by opposing factors, an analysis of variance should reveal it as an interaction between acceleration and other variables; however, no such interactions are found here. Tables are included emphasizing the pervasive influence of chronic centrifugation after only 12 days exposure.

Pitts, G. C.↗
NASA NTRS2018

Quantum Machine Learning

Quantum computing promises an unprecedented ability to solve intractable problems by harnessing quantum mechanical effects such as tunneling, superposition, and entanglement. The Quantum Artificial Intelligence Laboratory (QuAIL) at NASA Ames Research Center is the space agency's primary facility for conducting research and development in quantum information sciences. QuAIL conducts fundamental research in quantum physics but also explores how best to exploit and apply this disruptive technology to enable NASA missions in aeronautics, Earth and space sciences, and space exploration. At the same time, machine learning has become a major focus in computer science and captured the imagination of the public as a panacea to myriad big data problems. In this talk, we will discuss how classical machine learning can take advantage of quantum computing to significantly improve its effectiveness. Although we illustrate this concept on a quantum annealer, other quantum platforms could be used as well. If explored fully and implemented efficiently, quantum machine learning could greatly accelerate a wide range of tasks leading to new technologies and discoveries that will significantly change the way we solve real-world problems.

Biswas, Rupak↗
NASA NTRS1988

Multipoint measurements of energetic particles in the magnetosphere

The benefits of energetic-particle measurements in the study of magnetospheric physics are reviewed, including the particles' relative ease of detection, their high rectilinear speed, their range of gyroradii, and their immunity to large-scale electric fields. With such particles, it is possible to observationally separate distinctive plasma regions, uniquely assess field-line topologies, examine connectivity from the magnetospheric equator to the ionosphere, and sense global changes in magnetospheric configuration. Multipoint measurements of energetic particles have contributed substantially to the understanding of the earth magnetopause, the leakage of particles into the upstream region, the effect of sudden storm compressions, the global nature of substorm dynamics, and the location and character of high-energy acceleration processes.

Baker, D. N.↗
NASA NTRS2003

Recent Results From Internal and Very-Near-Field Plasma Diagnostics of a High Specific Impulse Hall Thruster

Floating potential and ion current density measurements were taken on the laboratory model NASA-173Mv2 in order to improve understanding of the physical processes affecting Hall thruster performance at high specific impulse. Floating potential was measured on discharge chamber centerline over axial positions spanning 10 mm from the anode to 100 mm downstream of the exit plane. Ion current density was mapped radially up to 300 mm from thruster centerline over axial positions in the very-near-field (10 to 250 mm from the exit plane). All data were collected using a planar probe in conjunction with a high-speed translation stage to minimize probe-induced thruster perturbations. Measurements of floating potential at a xenon flow rate of 10 mg/s have shown that the acceleration layer moved upstream 3 1 mm when the voltage increased from 300 to 600 V. The length of the acceleration layer was 14 2 mm and was approximately constant with voltage and magnetic field. Ion current density measurements indicated the annular ion beam crossed the thruster centerline 163 mm downstream of the exit plane. Radial integration of the ion current density at the cathode plane provided an estimate of the ion current fraction. At 500 V and 5 mg/s, the ion current fraction was calculated as 0.77.

Hofer, Richard R.↗
NASA NTRS1983

The Jovian magnetosphere

Research on Jovian magnetospheric physics from 1979 through 1982 is surveyed, with a focus on the observations of Voyagers 1 and 2. Jovian fields and plasmas are characterized in the order of their distance from the planet, and special emphasis is given to the Io plasma torus (IPT) in the 4.9-8-Jovian-radius region and to the extended Jovian magnetotail. Topics reviewed include synchrotron radiation, magnetic-field models, Na and S emissions in the IPT, aurora, the magnetic-anomaly model, IPT plasma diffusion-convection, Io-generated Alfven wave, plasma configuration beyond the IPT, low-energy charged particles, cosmic-ray-energy particles, particle acceleration, magnetic configuration, tail current sheet and plasma disc, magnetopause and magnetosheath, interplanetary ions of Jovian origin, and the Jovian magnetosphere at Saturnian distances.

Birmingham, T. J.↗
NASA NTRS1985

The physics of comets

This volume of the 'Fundamentals of Cosmic Physics' is concerned with the physics of comets. Aspects regarding the nucleus are discussed, taking into account observations, radius and albedo, mass, rotation, splitting and disruption, the temperature and sublimation of the cometary nucleus, the chemical composition, the electrostatic charging of the cometary nucleus, and the structure and evolution of the cometary nucleus. Other topics explored are related to the atmosphere and its interaction with the solar wind, the plasma tail, and the dust tail. Attention is given to excitation mechanisms, atmospheric abundances and production rates, chemical models of the inner coma, collisional processes and the multifluid approach, radiative transfer, the ionization processes, models of the inner layer, the outer coma, acceleration mechanisms in the plasma tail, the structure of the plasma tail, the cometary magnetosphere, dust grain orbits, gas-dust interaction in the inner coma, and the nature of the cometary dust.

Mendis, D. A.↗
NASA NTRS1998

SAMS-II Requirements and Operations

The Space Acceleration Measurements System (SAMS) II is the primary instrument for the measurement, storage, and communication of the microgravity environment aboard the International Space Station (ISS). SAMS-II is being developed by the NASA Lewis Research Center Microgravity Science Division to primarily support the Office of Life and Microgravity Science and Applications (OLMSA) Microgravity Science and Applications Division (MSAD) payloads aboard the ISS. The SAMS-II is currently in the test and verification phase at NASA LeRC, prior to its first hardware delivery scheduled for July 1998. This paper will provide an overview of the SAMS-II instrument, including the system requirements and topology, physical and electrical characteristics, and the Concept of Operations for SAMS-II aboard the ISS.

Wald, Lawrence W.↗
NASA NTRS2002

Effect of Gravity on the Near Field Flow Structure of Helium Jet in Air

Experiments have shown that a low-density jet injected into a high-density surrounding medium undergoes periodic oscillations in the near field. Although the flow oscillations in these jets at Richardson numbers about unity are attributed to the buoyancy, the direct physical evidence has not been acquired in the experiments. If the instability were indeed caused by buoyancy, the near-field flow structure would undergo drastic changes upon removal of gravity in the microgravity environment. The present study was conducted to investigate this effect by simulating microgravity environment in the 2.2-second drop tower at the NASA Glenn Research Center. The non-intrusive, rainbow schlieren deflectometry technique was used for quantitative measurements of helium concentrations in buoyant and non-buoyant jets. Results in a steady jet show that the radial growth of the jet shear layer in Earth gravity is hindered by the buoyant acceleration. The jet in microgravity was 30 to 70 percent wider than that in Earth gravity. The microgravity jet showed typical growth of a constant density jet shear layer. In case of a self-excited helium jet in Earth gravity, the flow oscillations continued as the jet flow adjusted to microgravity conditions in the drop tower. The flow oscillations were however not present at the end of the drop when steady microgravity conditions were reached.

Agrawal, Ajay K.↗
NASA NTRS2006

Getting a Kick Out of Numerical Relativity

Operating ground-based gravitational wave detectors and a planned instrument in space are bringing about the new field of gravitational wave astronomy. A prime source for any of these observatories is the merger of a system of two black holes. Brought together by copious losses of gravitational-wave energy, these systems merge in a burst of energy with a peak power exceeding any electromagnetic source. Observations of these sources will generate a wealth of astrophysical information, and may provide an unparalleled probe of strong-field gravitational physics, but a full interpretation of the observations will require detailed predictions from General Relativity. I will discuss recent advances in numerical simulations of binary black hole systems which are generating dramatic progress in understanding binary black hole mergers. Recent achievements include the first simulations of binary black hole systems through several orbits and merger, leading to detailed predictions for the final portion of the gravitational radiation waveforms from equal-mass mergers. For unequal-mass mergers, it has recently become possible to measure the impulsive kick imparted to the final black hole, by the asymmetry of the merger radiation. These first results announce an accelerating wave of progress soon to come from the energetic field of numerical relativity.

Source record↗
NASA NTRS2002

Monte Carlo transport model comparison with 1A GeV accelerated iron experiment: heavy-ion shielding evaluation of NASA space flight-crew foodstuff

Deep-space manned flight as a reality depends on a viable solution to the radiation problem. Both acute and chronic radiation health threats are known to exist, with solar particle events as an example of the former and galactic cosmic rays (GCR) of the latter. In this experiment Iron ions of 1A GeV are used to simulate GCR and to determine the secondary radiation field created as the GCR-like particles interact with a thick target. A NASA prepared food pantry locker was subjected to the iron beam and the secondary fluence recorded. A modified version of the Monte Carlo heavy ion transport code developed by Zeitlin at LBNL is compared with experimental fluence. The foodstuff is modeled as mixed nuts as defined by the 71st edition of the Chemical Rubber Company (CRC) Handbook of Physics and Chemistry. The results indicate a good agreement between the experimental data and the model. The agreement between model and experiment is determined using a linear fit to ordered pairs of data. The intercept is forced to zero. The slope fit is 0.825 and the R2 value is 0.429 over the resolved fluence region. The removal of an outlier, Z=14, gives values of 0.888 and 0.705 for slope and R2 respectively. c2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved.

NASA Discipline Radiation Health↗
NASA NTRS1989

Models of flaring loops

The somewhat questionable concept of an isolated flare loop and the various physical mechanisms believed to be responsible, to some degree, for energy transport within the loop structure is reviewed. Observational evidence suggests a predominant role for high-energy electrons as an energy transport mechanism, and the consequences of such a scenario is explored in some detail, focusing on radiation signatures in the soft X-ray, hard X-ray, and EUV wavebands, as observed by recent satellite observatories. It is found that the predictions of flare loop models are in fact in excellent agreement with these observations, reinforcing both the notion of the loop as a fundamental component of solar flares and the belief that electron acceleration is an integral part of the flare energy release process.

Emslie, A. Gordon↗
NASA NTRS2001

Coupled Growth in Hypermonotectics

The overall objective of this project is to obtain a fundamental understanding of the physics controlling solidification processes in immiscible alloy systems. The investigation involves both experimentation and the development of a model describing solidification in monotectic systems. The experimental segment was designed to first demonstrate that it is possible to obtain interface stability and steady state coupled growth in hypermonotectic alloys through microgravity processing. Microgravity results obtained to date have verified this possibility. Future flights will permit experimental determination of the limits of interface stability and the influence of alloy composition and growth rate on microstructure. The objectives of the modeling segment of the investigation include prediction of the limits of interface stability, modeling of convective flow due to residual acceleration, and the influence of surface tension driven flows at the solidification interface. The study of solidification processes in immiscible alloy systems is hindered by the inherent convective flow that occurs on Earth and by the possibility of sedimentation of the higher density immiscible liquid phase. It has been shown that processing using a high thermal gradient and a low growth rate can lead to a stable macroscopically planar growth front even in hypermonotectic alloys. Processing under these growth conditions can avoid constitutional supercooling and prevent the formation of the minor immiscible liquid phase in advance of the solidification front. However, the solute depleted boundary layer that forms in advance of the solidification front is almost always less dense than the liquid away from the solidification front. As a result, convective instability is expected. Ground based testing has indicated that convection is a major problem in these alloy systems and leads to gross compositional variations along the sample and difficulties maintaining interface stability. Sustained low gravity processing conditions are necessary in order to minimize these problems and obtain solidification conditions which approach steady state.

Andrews, J. Barry↗
NASA NTRS2016

Suited and Unsuited Hybrid III Impact Testing and Finite Element Model Characterization

NASA spacecraft design requirements for occupant protection are a combination of the Brinkley Dynamic Response Criteria and injury assessment reference values (IARV) extracted from anthropomorphic test devices (ATD). For the ATD IARVs, the requirements specify the use of the 5th percentile female Hybrid III and the 95th percentile male Hybrid III. Each of these ATDs is required to be fitted with an articulating pelvis (also known as the aerospace pelvis) and a straight spine. The articulating pelvis is necessary for the ATD to fit into spacecraft seats, while the straight spine is required as injury metrics for vertical accelerations are better defined for this configuration. Sled testing of the Hybrid III 5th Percentile Female Anthropomorphic Test Device (ATD) was performed at Wright-Patterson Air Force Base (WAPFB). Two 5th Percentile ATDs were tested, the Air Force Research Lab (AFRL) and NASA owned Hybrid III ATDs with aerospace pelvises. Testing was also conducted with a NASA-owned 95th Percentile Male Hybrid III with aerospace pelvis at WPAFB. Testing was performed using an Orion seat prototype provided by Johnson Space Center (JSC). A 5-point harness comprised of 2 inch webbing was also provided by JSC. For suited runs, a small and extra-large Advanced Crew Escape System (ACES) suit and helmet were also provided by JSC. Impact vectors were combined frontal/spinal and rear/lateral. Some pure spinal and rear axis testing was also performed for model validation. Peak accelerations ranged between 15 and 20-g. This range was targeted because the ATD responses fell close to the IARV defined in the Human-Systems Integration Requirements (HSIR) document. Rise times varied between 70 and 110 ms to assess differences in ATD responses and model correlation for different impact energies. The purpose of the test series was to evaluate the Hybrid III ATD models in Orion-specific landing orientations both with and without a spacesuit. The results of these tests were used by the NASA Engineering and Safety Center (NESC) to validate the finite element model (FEM) of the Hybrid III 5th Percentile Female ATD. Physical test data was compared to analytical predictions from simulations, and modelling uncertainty factors have been determined for each injury metric. Additionally, the test data has been used to further improve the FEM, particularly in the areas of the ATD preload, harness, and suit and helmet effects.

Lawrence, C.↗
NASA NTRS1985

Advanced ion thruster research

A series of experiments conducted on a ring cusp magnetic field ion thruster; in which the anode, cathode and discharge chamber backplate were moved relative to the magnetic cusp; are described. Optimum locations for the anode, cathode and backplate which yield the lowest energy cost per plasma ion and highest extracted ion fraction are identified. The results are discussed in terms of simple physical models. The results of preliminary experiments into the operation of hollow cathodes on nitrogen and xenon over a large pressure range (0.1 to 100 Torr) are presented. They show that the cathode discharge transfers from the cathode insert to the exterior edge of the orifice plate as the interelectrode pressure is increased. Experimental evidence showing that a new ion extractor grid concept can be used to stabilize the plasma sheath at the screen grid is presented. This concept, identified by the term constrained sheath optics, is shown to hold ion beamlet divergence and impingement characteristics to stable values as the beamlet current and the net and total accelerating voltages are changed. The current status of a study of beamlet vectoring induced by displacing the accelerator and/or decelerator grids of a three grid ion extraction system relative to the screen grid is discussed.

Wilbur, P. J.↗
NASA NTRS1991

Plastic scintillator block as photon beam monitor for EGRET calibration

The EGRET (Energetic Gamma Ray Experiment Telescope) detector has been calibrated at SLAC (Stanford Linear Accelerator) and, to a lesser degree, at the MIT Bates Linear Accelerator Center. To monitor the photon beams for the calibration, a plastic scintillator block, 5 cm x 5 cm in cross section, 15 cm in length, and viewed by a single photomultiplier tube, was used for the entire beam energy range of 15 MeV to 10 GeV. The design operation, and method of analysis of the beam intensity are presented. A mathematical framework has been developed to treat the general case of a beam with multiphoton beam pulses and with a background component. A procedure to deal with the fluctuations of the beam intensity over a data-taking period was also developed. The photon beam monitor is physically sturdy, electronically steady, simple to construct, and easy to operate. Its major merits lie in its sheer simplicity of construction and operation and in the wide energy range it can cover.

Lin, Y. C.↗