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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Quantum state transfer in double-quantum-well devices

A Monte Carlo simulation of double-quantum-well (DQW) devices is presented in view of analyzing the quantum state transfer (QST) effect. Different structures, based on the AlGaAs/GaAs system, were simulated at 77 and 300 K and optimized in terms of electron transfer and device speed. The analysis revealed the dominant role of the impurity scattering for the QST. Different approaches were used for the optimization of QST devices and basic physical limitations were found in the electron transfer between the QWs. The maximum transfer of electrons from a high to a low mobility well was at best 20%. Negative differential resistance is hampered by the almost linear rather than threshold dependent relation of electron transfer on electric field. By optimizing the doping profile the operation frequency limit could be extended to 260 GHz.

Jakumeit, Jurgen↗
NASA NTRS1973

Survival of bacterial isolates exposed to simulated Jovian trapped radiation belt electrons and solar wind protons

With missions to Jupiter, the spacecraft will be exposed for extended durations to solar wind radiation and the Jovian trapped radiation belt. This study is designed to determine the effect of these radiation environments on spacecraft bacterial isolates. The information can be used in the probability of contamination analysis for these missions. A bacterial subpopulation from Mariner Mars 1971 spacecraft (nine spore-forming and three non-spore-forming isolates) plus two comparative organisms, Staphylococcus epidermidis ATCC 17917 and a strain of Bacillus subtilis var. niger, were exposed to 2, 12, and 25 MeV electrons at different doses with simultaneous exposure to a vacuum of 1.3 x 10(-4) N m-2 at 20 and -20 degrees C. The radioresistance of the subpopulation was dependent on the isolate, dose and energy of electrons. Temperature affected the radioresistance of only the spore-forming isolates. Survival data indicated that spores were reduced approximately 1 log/1500 J kg-1 (10 J kg-1=1 krad), while non-spore-forming isolates (micrococci) were reduced 1.5-2 logs/1500 J kg-1 with the exception of an apparent radioresistant isolate whose resistance approached that of the spores. The subpopulation was found to be less resistant to lower energy than to higher energy electrons. The bacterial isolates were exposed to 3 keV protons under the same conditions as the electrons with a total fluence of 1.5 x 10(13) p cm-2 and a dose rate of 8.6 x 10(9) p cm-2 s-1. The results showed that only 20% of S. epidermidis and 45% of B. subtilis populations survived exposure to the 3 keV protons, while the mean survival of the spacecraft subpopulation was 45% with a range from 31.8% (non-spore-former) to 64.8% (non-spore-former). No significant difference existed between spore-forming and non-spore-forming isolates.

Electrons↗
NASA NTRS1966

Radiation used to temperature compensate semiconductor strain gages

Exposure to high energy electron radiation reduces the temperature coefficients of resistance and gage factor of a range of resistivities of n- and p-type semiconductor silicon strain gages. After irradiation, the gages are heated to a high temperature for a 24-hour period to stabilize their temperature coefficients.

Gross, C.↗
NASA NTRS1973

On the Design and Test of a Liquid Injection Electric Thruster

A liquid injection electric thruster (LINJET) was designed and tested. The results of the tests were very encouraging with thruster performance levels well in excess of design goals. Supporting activities to the engine design and test included a five-million pulse life test on the main capacitor, a 46-million pulse test on the trigger electronics, design and fabrication of a zero resistance torque connector for use with the torsional pendulum thrust stand, design and fabrication of a logic box for control of engine firing, and a physical and chemical properties characterization of the perfluorocarbon propellant. While the results were encouraging, testing was limited, as many problems existed with the design. The most significant problem was involved with excessive propellant flow which contributed to false triggering and shorting. Low power active thermal control of the propellant storage cavity, coupled with a re-evaluation of the injection ring pore size and area exposed to the main capacitor discharge are areas that should be investigated should this design be carried forward.

Jones, T. A.↗
NASA NTRS1975

Ternary compound thin film solar cells

A group of ternary compound semiconductor (I-III-VI2) thin films for future applications in photovoltaic devices is proposed. The consideration of these materials (CuInSe2, CuInTe2 and especially CuInS2) for long range device development is emphasized. Much of the activity to date has been concerned with the growth and properties of CuInX2 films. X-ray and electron diffraction analyses, Hall mobility and coefficient, resistivity and carrier concentration variations with substrate and film temperature as well as grain size data have been determined. Both p- and n-type films of CuInS2 and CuInSe2 have been produced. Single and double source deposition techniques have been utilized. Some data have been recorded for annealed films.

Kazmerski, L. L.↗
NASA NTRS1979

Thermoelectrically-cooled variable-temperature probe

Variable-temperature probe for electron spectroscopy requires no cryogenic liquids or resistance heating elements. Device consists of heat sink, probe tip, and nickel-plated copper body which resists oxidation and transfers heat efficiently between tip and heat sink.

Kelso, R. M.↗
NASA NTRS1977

Factors affecting laser-trim stability of thick film resistors

Various factors affecting precision of trim and resistor stability were considered. The influence of machine operating parameters on resistor performance was examined and quantified through statistically designed experiments for a Q switched YAG laser system. Laser kerf quality was studied by scanning electron microscopy and related to kerf isolation resistance measurements. A relatively simple production oriented, quality control test is proposed for rapid determination of kerf electrical stability. In addition, the effect of cut design and extent of trim on precision and stability were discussed.

Cote, R. E.↗
NASA NTRS1980

GaAs homojunction solar cell development

The Lincoln Laboratory n(+)/p/p(+) GaAs shallow homojunction cell structure was successfully demonstrated on 2 by 2 cm GaAs substrates. Air mass zero efficiencies of the seven cells produced to date range from 13.6 to 15.6 percent. Current voltage (I-V) characteristics, spectral response, and measurements were made on all seven cells. Preliminary analysis of 1 MeV electron radiation damage data indicate excellent radiation resistance for these cells.

Flood, D. J.↗
NASA NTRS1984

The influence of hold times on LCF and FCG behavior in a P/M Ni-base superalloy

The relative importance of creep and environmental interactions in high temperature fatigue behavior has been investigated for as-HIP Rene 95. Strain-controlled low cycle fatigue and load-controlled fatigue crack growth tests were performed at elevated temperatures in argon, followed by fractographic analyses of the fracture surfaces by scanning electron microscopy. Fatigue lives were drastically reduced and crack growth rates increased one hundred fold as a result of superposition of hold times on continuous cycling. A change in fracture mode with hold time also was noted. Chromium oxide was detected on the fracture surface by Auger electron spectroscopy. The drastic changes in fatigue resistance due to hold times were attributed primarily to environmental interactions with fatigue processes.

Choe, S. J.↗
NASA NTRS1986

Simulations of collisionless shocks

A problem of critical importance to space and astrophysics is the existence and properties of high-Mach-number shocks. In this letter the results of simulations of perpendicular shocks with Alfven Mach number 22 are presented. It is shown that the shock structure is a sensitive function of resistivity, becoming turbulent when the resistivity is too low. The problem of electron heating, and the extension of the results to higher Mach numbers are discussed.

Quest, K. B.↗
NASA NTRS1989

Progress in indium phosphide solar cell research

Progress, dating from the start of the Lewis program, is reviewed emphasizing processing techniques which have achieved the highest efficiencies in a given year. To date, the most significant achievement has been attainment of AM0 total area efficiencies approaching 19 percent. Although closed tube diffusion is not considered to be an optimum process, reasonably efficient 2cm x 2cm and 1cm x 2cm InP cells have been produced in quantity by this method with a satellite to be launched in 1990 using these cells. Proton irradiation of these relatively large area cells indicates radiation resistance comparable to that previously reported for smaller InP cells. A similar result is found for the initial proton irradiations of ITO/InP cells processed by D. C. sputtering. With respect to computer modelling, a comparison of n/p homojunction InP and GaAs cells of identical geometries and dopant concentrations has confirmed the superior radiation resistance of InP cells under 1 MeV electron irradiations.

Weinberg, Irving↗
NASA NTRS1988

Switch-on shocks

It is argued that parallel propagating Alfven waves steepen to second order in the wave amplitude, rather than first order, as is the case for oblique MHD waves. An analytical solution for the structure of weak switch-on shocks is derived. The Rankine-Hugoniot relations for finite amplitude switch-on shocks are obtained in a compact form. The differential equation for resistive switch-on shocks is solved, and the resistive critical Mach number is obtained. The differential equation for resistive switch-on shocks with finite ion inertia is identical to the one obtained in the pure resistive case. It is argued that efficient electron heat conduction can significantly extend the range of upstream parameters for which switch-on shocks are expected.

Kennel, C. F.↗
NASA NTRS1992

High performance polymers and polymer matrix composites for spacecraft structural applications

A program implemented by NASA Langley Research Center to develop and evaluate new polymers and polymer matrix composites for spacecraft structural applications is examined. Various polymeric films, moldings, and adhesives are evaluated for resistance to atomic oxygen and high energy electron and UV radiation. Thin films from the poly(arylene ether)s containing phenylphosphine oxide groups and the siloxane-epoxies exhibited minor weight loss compared to Kapton polyimide after exposure. Large doses (greater than 10 exp 9 rads) of electron radiation, simulating 30 yr of exposure in GEO, are found to alter the chemical structure of epoxies by both chain scission and cross-linking. The thermal cycling representative of both LEO and GEO environments can cause microcracking in composites which can in turn affect the dimensional stability and produce mechanical property reductions. The processing and fabrication issues associated with precision composite spacecraft components are also addressed.

Bowles, D. E.↗
NASA NTRS1996

Mechanics Methodology for Textile Preform Composite Materials

NASA and its contractors have completed a program to develop a basic mechanics underpinning for textile composites. Three major deliverables were produced by the program: 1. A set of test methods for measuring material properties and design allowables; 2. Mechanics models to predict the effects of the fiber preform architecture and constituent properties on engineering moduli, strength, damage resistance, and fatigue life; and 3. An electronic data base of coupon type test data. This report describes these three deliverables.

Poe, Clarence C., Jr.↗