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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Optimization of composite structures

Structural optimization is introduced and examples which illustrate potential problems associated with optimized structures are presented. Optimized structures may have very low load carrying ability for an off design condition. They tend to have multiple modes of failure occurring simultaneously and can, therefore, be sensitive to imperfections. Because composite materials provide more design variables than do metals, they allow for more refined tailoring and more extensive optimization. As a result, optimized composite structures can be especially susceptible to these problems.

Stroud, W. J.↗
NASA NTRS1982

Basis for equivalent fluence concept in space solar cells

The equivalent fluence concept is defined, and its use and potential problems are noted. Silicon and GaAs solar cells are compared in a radiation environment. The analysis indicates that valid equivalent fluence values may be easier to obtain in GaAs than in silicon.

Meulenberg, A.↗
NASA NTRS1983

Future of alternate fuels for turbine engines

The fuel property variations that were identified to be of concern with the utilization of alternate fuels for aircraft turbine engines are related to the potential problem areas.

Schelp, H.↗
NASA NTRS1983

ECUT: Energy Conversion and Utilization Technologies program biocatalysis research activity. Potential membrane applications to biocatalyzed processes: Assessment of concentration polarization and membrane fouling

Separation and purification of the products of biocatalyzed fermentation processes, such as ethanol or butanol, consumes most of the process energy required. Since membrane systems require substantially less energy for separation than most alternatives (e.g., distillation) they have been suggested for separation or concentration of fermentation products. This report is a review of the effects of concentration polarization and membrane fouling for the principal membrane processes: microfiltration, ultrafiltration, reverse osmosis, and electrodialysis including a discussion of potential problems relevant to separation of fermentation products. It was concluded that advanced membrane systems may result in significantly decreased energy consumption. However, because of the need to separate large amounts of water from much smaller amounts of product that may be more volatile than wate, it is not clear that membrane separations will necessarily be more efficient than alternative processes.

Ingham, J. D.↗
NASA NTRS1983

Analysis of the reflective multibandgap solar cell concept

A new and unique approach to improving photovoltaic conversion efficiency, the reflective multiband gap solar cell concept, was examined. This concept uses back surface reflectors and light trapping with several physically separated cells of different bandgaps to make more effective use of energy from different portions of the solar spectrum. Preliminary tests performed under General Dynamics Independent Research and Development (IRAD) funding have demonstrated the capability for achieving in excess of 20% conversion efficiency with aluminum gallium arsenide and silicon. This study analyzed the ultimate potential for high conversion efficiency with 2, 3, 4, and 5 different bandgap materials, determined the appropriate bandgaps needed to achieve this optimized efficiency, and identified potential problems or constraints. The analysis indicated that an improvement in efficiency of better than 40% could be attained in this multibandgap approach, compared to a single bandgap converter under the same assumptions. Increased absorption loss on the back surface reflector was found to incur a minimal penalty on efficiency for two and three bandgap systems. Current models for bulk absorption losses in 3-5 materials were found to be inadequate for explaining laboratory observed transmission losses. Recommendations included the continued development of high bandgap back surface reflector cells and basic research on semiconductor absorption mechanisms.

Stern, T. G.↗
NASA NTRS1982

'Light bar' attitude indicator

The development and evaluation of a light bar attitude indicator to help maintain proper aircraft attitude during high altitude night flying is described. A standard four-inch ADI was modified to project an artificial horizon across the instrument panel for pitch and roll information. A light bulb was put in the center of the ADI and a thin slit cut on the horizon, resulting in a thin horizontal sheet of light projecting from the instrument. The intensity of the projected beam is such that it can only be seen in a darkened room or at night. The beam on the instrument panel of the T-37 jet trainer is shown, depicting various attitudes. The favorable comments of about 50 pilots who evaluated the instrument are summarized, including recommendations for improving the instrument. Possible uses for the instrument to ease the pilot task are listed. Two potential problems in using the device are the development of pilot complacency and an upright-inverted ambiguity in the instrument.

Enevoldson, E. K.↗
NASA NTRS1983

Pyroelectric conversion in space: A conceptual design study

Pyroelectric conversion is potentially a very lightweight means of providing electrical power generation in space. Two conceptualized systems approaches for the direct conversion of heat (from sunlight) into electrical energy using the pyroelectric effect of a new class of polar polymers were evaluated. Both of the approaches involved large area thin sheets of plastic which are thermally cycled by radiative input and output of thermal energy. The systems studied are expected to eventually achieve efficiencies of the order of 8% and may deliver as much as one half kilowatt per kilogram. In addition to potentially very high specific power, the pyroelectric conversion approaches outlined appear to offer low cost per watt in the form of an easily deployed, flexible, strong, electrically ""self-healing'', and high voltage sheet. This study assessed several potential problems such as plasma interactions and radiation degradation and suggests approaches to overcome them. The fundamental technological issues for space pyroelectric conversion are: (1) demonstration of the conversion cycle with the proposed class of polymers, (2) achievement of improved dielectric strength of the material, (3) demonstration of acceptable plasma power losses for low altitude, and (4) establishment of reasonable lifetime for the pyroelectric material in the space environment. Recommendations include an experimental demonstration of the pyroelectric conversion cycle followed by studies to improve the dielectric strength of the polymer and basic studies to discover additional pyroelectric materials.

Olsen, R. B.↗
NASA NTRS1983

Ada and the NASA software environment

The NASA software, in broad categories, is described, and the software life cycle is characterized. Programming language policy and practices are reviewed. Applicability, benefits, and transition, as well as present and potential problems with Ada are examined.

Ng, E. W.↗
NASA NTRS1984

Thermal detectors as X-ray spectrometers

Sensitive thermal detectors should be useful for measuring very small energy pulses, such as those produced by the absorption of X-ray photons. The measurement uncertainty can be very small, making the technique promising for high resolution nondispersive X-ray spectroscopy. The limits to the energy resolution of such thermal detectors are derived and used to find the resolution to be expected for a detector suitable for X-ray spectroscopy in the 100 eV to 10,000 eV range. If there is no noise in the thermalization of the X-ray, resolution better than 1 eV full width at half maximum is possible for detectors operating at 0.1 K. Energy loss in the conversion of the photon energy to heat is a potential problem. The loss mechanisms may include emission of photons or electrons, or the trapping of energy in long lived metastable states. Fluctuations in the phonon spectrum could also limit the resolution if phonon relaxation times are very long. Conceptual solutions are given for each of these possible problems.

Moseley, S. H.↗
NASA NTRS1984

Evaluation of the HARDMAN comparability methodology for manpower, personnel and training

The methodology evaluation and recommendation are part of an effort to improve Hardware versus Manpower (HARDMAN) methodology for projecting manpower, personnel, and training (MPT) to support new acquisition. Several different validity tests are employed to evaluate the methodology. The methodology conforms fairly well with both the MPT user needs and other accepted manpower modeling techniques. Audits of three completed HARDMAN applications reveal only a small number of potential problem areas compared to the total number of issues investigated. The reliability study results conform well with the problem areas uncovered through the audits. The results of the accuracy studies suggest that the manpower life-cycle cost component is only marginally sensitive to changes in other related cost variables. Even with some minor problems, the methodology seem sound and has good near term utility to the Army. Recommendations are provided to firm up the problem areas revealed through the evaluation.

Zimmerman, W.↗
NASA NTRS1983

Optimization of composite structures

Structural optimization is introduced and examples which illustrate potential problems associated with optimized structures are presented. Optimized structures may have very low load carrying ability for an off design condition. They tend to have multiple modes of failure occurring simultaneously and can, therefore, be sensitive to imperfections. Because composite materials provide more design variables than do metals, they allow for more refined tailoring and more extensive optimization. As a result, optimized composite structures can be especially susceptible to these problems. Previously announced in STAR as N83-10447

Stroud, W. J.↗
NASA NTRS1984

Thermal detectors as X-ray spectrometers

Sensitive thermal detectors should be useful for measuring very small energy pulses, such as those produced by the absorption of X-ray photons. The measurement uncertainty can be very small, making the technique promising for high resolution nondispersive X-ray spectroscopy. The limits to the energy resolution of such thermal detectors are derived and used to find the resolution to be expected for a detector suitable for X-ray spectroscopy in the 100 eV to 10,000 eV range. If there is no noise in the thermalization of the X-ray, resolution better than 1 eV full width at half maximum is possible for detectors operating at 0.1 K. Energy loss in the conversion of the photon energy to heat is a potential problem. The loss mechanisms may include emission of photons or electrons, or the trapping of energy in long lived metastable states. Fluctuations in the phonon spectrum could also limit the resolution if phonon relaxation times are very long. Conceptual solutions are given for each of these possible problems.

Moseley, S. H.↗
NASA NTRS1985

Electronics systems test laboratory testing of shuttle communications systems

Shuttle communications and tracking systems space to space and space to ground compatibility and performance evaluations are conducted in the NASA Johnson Space Center Electronics Systems Test Laboratory (ESTL). This evaluation is accomplished through systems verification/certification tests using orbiter communications hardware in conjunction with other shuttle communications and tracking external elements to evaluate end to end system compatibility and to verify/certify that overall system performance meets program requirements before manned flight usage. In this role, the ESTL serves as a multielement major ground test facility. The ESTL capability and program concept are discussed. The system test philosophy for the complex communications channels is described in terms of the major phases. Results of space to space and space to ground systems tests are presented. Several examples of the ESTL's unique capabilities to locate and help resolve potential problems are discussed in detail.

Stoker, C. J.↗
NASA NTRS1985

Orbital Debris

Earth orbital debris issues and recommended future activities are discussed. The workshop addressed the areas of environment definition, hazards to spacecraft, and space object management. It concluded that orbital debris is a potential problem for future space operations. However, before recommending any major efforts to control the environment, more data are required. The most significant required data are on the population of debris smaller than 4 cm in diameter. New damage criteria are also required. When these data are obtained, they can be combined with hypervelocity data to evaluate the hazards to future spacecraft. After these hazards are understood, then techniques to control the environment can be evaluated.

Donald J. Kessler↗
NASA NTRS1985

Icing tunnel tests of Electro-Impulse De-Icing of an engine inlet and high-speed wings

A brief review is given of four earlier tests in the NASA Lewis Icing Research Tunnel and of flight tests in NASA's Icing Research Aircraft and in a Cessna 206 airplane. Details are given of recent icing tunnel tests of thicker-skinned wings, a Gates Learjet, a composite leading edge, and a Boeing 767, and of a Falcon Fanjet engine inlet. These were tested at speeds from 87 to 220 knots, air temperatures from -2 to -15 C, LWC values of 0.6 to 2.4 grams/cu meter, and median droplet diameters from 12 to 20 microns. Energy requirements are reported, as well as conclusions from comparisons of several Electro-Impulse De-Icing coil system designs. Fundamental studies of the structural dynamics and ice shedding of a 12.7 cm (5 inch) diameter semicylinder are described. Some potential problem areas are discussed: fatigue of skin and coil mountings, system weight and cost, electro-magnetic interference and noise.

Zumwalt, G. W.↗
NASA NTRS1985

The energization of electrons and ions by electron beams injected in the ionosphere

This paper represents a continuation of an investigation of the nature and origin of the particle populations associated with an electron beam-emitting rocket experiment in the ionosphere. In this investigation, the intense flux of suprathermal electrons created around such a rocket has been studied by several groups. Arnoldy and Winckler (1981) have discussed the vehicle floating potential problem. The present paper is concerned with results which have been obtained from the Echo 4 and 5 experiments considered by Swanson (1983). Attention is given to instrumentation, suprathermal electrons, thermal ions, energetic ions, and ion resonances.

Arnoldy, R. L.↗
NASA NTRS1983

A study of some features of ac and dc electric power systems for a space station

This study analyzes certain selected topics in rival dc and high frequency ac electric power systems for a Space Station. The interaction between the Space Station and the plasma environment is analyzed, leading to a limit on the voltage for the solar array and a potential problem with resonance coupling at high frequencies. Certain problems are pointed out in the concept of a rotary transformer, and further development work is indicated in connection with dc circuit switching, special design of a transmission conductor for the ac system, and electric motors. The question of electric shock hazards, particularly at high frequency, is also explored. and a problem with reduced skin resistance and therefore increased hazard with high frequency ac is pointed out. The study concludes with a comparison of the main advantages and disadvantages of the two rival systems, and it is suggested that the choice between the two should be made after further studies and development work are completed.

Hanania, J. I.↗