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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 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Study of monopropellants for electrothermal thrusters

A 333 mN electrothermal thruster designed to use MIL-grade hydrazine was demonstrated to be suitable for operation with low freezing point monopropellants containing hydrazine azide, monomethylhydrazine, unsymmetrical-dimethylhydrazine and ammonia. The steady-state specific impulse was greater than 200 sec for all propellants. The pulsed-mode specific impulse for an azide blend exceeded 175 sec for pulse widths greater than 50 msec; propellants containing carbonaceous species delivered 175 sec pulsed-mode specific impulses for pulse widths greater than 100 msec. Longer thrust chamber residence times were required for the carbonaceous propellants; the original thruster design was modified by increasing the characteristic chamber length and screen packing density. Specific recommendations were made for the work required to design and develop flight worthy thrusters, including methods to increase propellant dispersal at injection, thruster geometry changes to reduce holding power levels and methods to initiate the rapid decomposition of the carbonaceous propellants.

Kuenzly, J. D.↗
NASA NTRS1975

Applications of Landsat imagery to geological research in Minnesota

A large part of northeastern Minnesota north of Lake Superior was studied using Landsat images. The area is being studied for its intercontinental rift and for large, low grade, copper-nickel deposits. By using Landsat imagery in conjunction with field data, it is possible to develop a much higher level of continuity and structural resolution in interpretations of the bedrock geology. Preliminary results indicate that it is possible to distinguish various surficial morphological features such as the Vermilion and Highland moraines, the Toimi drumlin field, and an unnamed drumlin field apparently associated with the Highland moraine.

Weiblen, P. W.↗
NASA NTRS1975

Design and implementation of a medium speed communications interface and protocol for a low cost, refreshed display computer

The design and implementation of hardware and software systems involved in using a 40,000 bit/second communication line as the connecting link between an IMLAC PDS 1-D display computer and a Univac 1108 computer system were described. The IMLAC consists of two independent processors sharing a common memory. The display processor generates the deflection and beam control currents as it interprets a program contained in the memory; the minicomputer has a general instruction set and is responsible for starting and stopping the display processor and for communicating with the outside world through the keyboard, teletype, light pen, and communication line. The processing time associated with each data byte was minimized by designing the input and output processes as finite state machines which automatically sequence from each state to the next. Several tests of the communication link and the IMLAC software were made using a special low capacity computer grade cable between the IMLAC and the Univac.

Phyne, J. R.↗
NASA NTRS1975

Crawler Transporter Steering and Jel Systems

The transporter weighing 2.8 million kilograms (6.3 million pounds) was used to lift a 5.7-million-kilogram (12.6-million-pound) combination of mobile launcher and space vehicle, transfer this load approximately 5.6 kilometers (3.5 miles) from its point of assembly, negotiate curves of 152-meter (500-foot) mean radius, climb a 5-percent grade while maintaining the 122-meter (400-foot) structure in a vertical position within 10 minutes of arc, and smoothly position this huge structure to within plus or minus 5.1 centimeters (plus or minus 2 inches) on support pedestals at the launch pad. The crawler-transporter is described in detail.

Davis, V. L.↗
NASA NTRS1975

Epitaxial solar cells fabrication

Silicon epitaxy has been studied for the fabrication of solar cell structures, with the intent of optimizing efficiency while maintaining suitability for space applications. SiH2CL2 yielded good quality layers and junctions with reproducible impurity profiles. Diode characteristics and lifetimes in the epitaxial layers were investigated as a function of epitaxial growth conditions and doping profile, as was the effect of substrates and epitaxial post-gettering on lifetime. The pyrolytic decomposition of SiH4 was also used in the epitaxial formation of highly doped junction layers on bulk Si wafers. The effects of junction layer thickness and bulk background doping level on cell performance, in particular, open-circuit voltage, were investigated. The most successful solar cells were fabricated with SiH2 CL2 to grow p/n layers on n(+) substrates. The best performance was obtained from a p(+)/p/n/n(+) structure grown with an exponential grade in the n-base layer.

Daiello, R. V.↗
NASA NTRS1975

Improving the toughness of refractory compounds

Composition and processing studies were conducted on silicon nitride and silicon carbide materials. Charpy mode impact testing to 2415 F established the effectiveness of higher purity silicon nitride powder sources in reducing the scatter of measurements and in improving short time bend strengths as well as bend stress rupture properties. Stabilized zirconia additions in particular were observed to dramatically enhance low and high temperature bend strengths and stress rupture properties for all grades of silicon nitride powder. Silicon carbide samples showed relatively poor impact resistance, although the maxima in stress rupture behavior was exhibited by this material.

Vasilos, T.↗
NASA NTRS1976

Third Working Meeting on Gallium Arsenide Solar Cells

Research results are reported for GaAs Schottky barrier solar cells, GaAlAs/GaAs heteroface solar cells, and GaAlAs graded band gap solar cells. Related materials studies are presented. A systems study for GaAs and Si solar concentrator systems is given.

Walker, G. H.↗
NASA NTRS1974

Simulated lightning test shuttle .03 scale model

Lightning Attach Point tests were conducted for the space shuttle launch configuration (Orbiter, External Tank and Solid Rocket Boosters). A series of 250 long spark tests (15 to 20 foot sparks) determined that the orbiter may be struck on the nose, windshield brow, tail and wingtips during launch but not on the main engine nozzles which have been shown to be vulnerable to lightning damage. The orbiter main engine and SRB exhaust plumes were simulated electrically with physical models coated with graded resistance paints. The tests showed that the exhaust plumes from the SRB provide additional protection for the main engine nozzles. However, the tests showed that the Orbiter Thermal Protection System (TPS), which has also been shown to be vulnerable to lightning damage, may be struck during launch. Therefore further work is indicated in the areas of swept stroke studies on the model and on TPS panels. Further attach point testing is also indicated on the free-flying orbiter. Photographs of the test setup are shown.

Clifford, D. W.↗
NASA NTRS1976

Silicon materials task of the low cost solar array project, part 2

Purity requirements for solar cell grade silicon material was developed and defined by evaluating the effects of specific impurities and impurity levels on the performance of silicon solar cells. Also, data was generated forming the basis for cost-tradeoff analyses of silicon solar cell material. Growth, evaluation, solar cell fabrication and testing was completed for the baseline boron-doped Czochralski material. Measurements indicate Cn and Mn seriously degrade cell performance, while neither Ni nor Cu produce any serious reduction in cell efficiency.

Hopkins, R. H.↗
NASA NTRS1976

Evaluation of selected chemical processes for production of low-cost silicon

Plant construction costs and manufacturing costs were estimated for the production of solar-grade silicon by the reduction of silicon tetrachloride in a fluidized bed of seed particles, and several modifications of the iodide process using either thermal decomposition on heated filaments (rods) or hydrogen reduction in a fluidized bed of seed particles. Energy consumption data for the zinc reduction process and each of the iodide process options are given and all appear to be acceptable from the standpoint of energy pay back. Information is presented on the experimental zinc reduction of SiCl4 and electrolytic recovery of zinc from ZnCl2. All of the experimental work performed thus far has supported the initial assumption as to technical feasibility of producing semiconductor silicon by the zinc reduction or iodide processes proposed. The results of a more thorough thermodynamic evaluation of the iodination of silicon oxide/carbon mixtures are presented which explain apparent inconsistencies in an earlier cursory examination of the system.

Blocher, J. M., Jr.↗
NASA NTRS1976

Report of 14-day bedrest simulation of Skylab

Part one of a two-phase bedrest project in which the physiological effects of weightlessness were simulated is presented. The project was designed to approximate the medical testing and dietary control of Skylab. The test period included a three week pre-flight period, a two week bedrest period and a two week post-flight period. The test subjects ate measured amounts of the Skylab diet and drank deionized water to recreate the metabolic balance studies of Skylab. The medical testing program, pre- and postbedrest, was similar to that of Skylab including: lower body negative pressure testing the orthostatic intolerance noted after both spaceflights and bedrest, bicycle ergometry testing the cardiovascular response to graded exercise, postural equilibrium, vestibular studies and electromyograms. Fluid and electrolyte shifts and balance were documented with intake and output records and radionuclide studies. The subjects were observed by a psychiatrist who watched for signs of mental stress in the test environment and changes in mental status.

Johnson, P. C.↗
NASA NTRS1976

Fabrication of polycrystalline solar cells on low-cost substrates

A new method of producing p-n junction semiconductors for solar cells was described; the principal objective of this investigation is to reduce production costs significantly by depositing polycrystalline silicon on a relatively cheap substrate such as metallurgical-grade silicon, graphite, or steel. The silicon layer contains appropriate dopants, and the substrates are coated with a diffusion barrier of silica, borosilicate, phosphosilicate, or mixtures of these compounds.

Chu, T. L.↗
NASA NTRS1976

Graphite and ablative material response to CO2 laser, carbon-arc, and xenon-arc radiation

The behavior was investigated of graphite and several charring ablators in a variety of high-radiative heat-flux environments. A commercial-grade graphite and nine state-of-the-art charring ablators were subjected to various radiative environments produced by a CO2 laser and a carbon arc. Graphite was also tested in xenon-arc radiation. Heat-flux levels ranged from 10 to 47 MW/sq m. Tests were conducted in air, nitrogen, helium, and a CO2-N2 mixture which simulated the Venus atmosphere. The experimental results were compared with theoretical results obtained with a one-dimensional charring-ablator analysis and a two-dimensional subliming-ablator analysis. Neither the graphite nor the charring ablators showed significant differences in appearance or microstructure after testing in the different radiative environments. The performance of phenolic nylon and graphite was predicted satisfactorily with existing analyses and published material property data. Good agreement between experimental and analytical results was obtained by using sublimation parameters from a chemical nonequilibrium analysis of graphite sublimation. Some charring ablators performed reasonably well and could withstand radiative fluxes of the level encountered in certain planetary entries. Other materials showed excessive surface recession and/or large amounts of cracking and spalling, and appear to be unsuitable for severe radiative environments.

Brewer, W. D.↗
NASA NTRS1976

Assessment of NDE Reliability Data

Twenty sets of relevant Nondestructive Evaluation (NDE) reliability data have been identified, collected, compiled, and categorized. A criterion for the selection of data for statistical analysis considerations has been formulated. A model to grade the quality and validity of the data sets has been developed. Data input formats, which record the pertinent parameters of the defect/specimen and inspection procedures, have been formulated for each NDE method. A comprehensive computer program has been written to calculate the probability of flaw detection at several confidence levels by the binomial distribution. This program also selects the desired data sets for pooling and tests the statistical pooling criteria before calculating the composite detection reliability. Probability of detection curves at 95 and 50 percent confidence levels have been plotted for individual sets of relevant data as well as for several sets of merged data with common sets of NDE parameters.

Yee, B. G. W.↗
NASA NTRS1975

Prostaglandin control of renal circulation in the unanesthetized dog and baboon

Effects of indomethacin and meclofenamate, inhibitors of prostaglandin synthesis, were evaluated in the regulation of renal blood flow in conscious and anesthetized dogs and in tranquilized baboons, instrumented with arterial pressure catheters and renal blood flow probes. Indomethacin, 10 mg/kg, did not alter renal blood flow or resistance significantly in the conscious dog. In the anesthetized dog, however, indomethacin caused a reduction in renal blood flow and an elevation of renal vascular resistance. Meclofenamate, 4 mg/kg, reduced renal flow and increased renal vascular resistance in conscious dogs. In conscious dogs and tranquilized primates, indomethacin and meclofenamate reduced the reactive hyperemia in the renal bed. Methoxamine and angiotensin II infused in graded doses induced significantly greater renal vasoconstriction in conscious dogs in the presence of indomethacin. Thus, in the conscious animal, prostaglandins appear to play only a minor part in the control of renal circulation at rest, but they are of greater importance in mediating the renal responses to reactive hyperemia and to vasoconstriction.

Swain, J. A.↗
NASA NTRS1975

Solar house system interfaced with the power utility grid

Photovoltaic cells may be used to convert sunlight directly into electrical energy and into low-grade heat to be used for large scale terrestrial solar energy conversion. Both forms of energy can be utilized if such cells are deployed in close proximity to the consumer (rooftop). CdS/Cu2S solar cells are an example of cells which may be produced inexpensively enough to become economically attractive. Cell parameters relevant for combined solar conversion are presented. Critical issues, such as production yield, life expectancy, stability of performance, are discussed. Systems design parameters related to operating temperatures are analyzed. First results obtained on Solar One, the experimental solar house of the University of Delaware, are given. Economic aspects are discussed.

Boeer, K. W.↗
NASA NTRS1976

Epitaxial silicon solar cells

P+/p/n/n+ epitaxial silicon solar-cell structures were fabricated with the n-base region intentionally graded over 2 orders of magnitude in a thickness of 35 microns. Solar cells made from these layers exhibited near-ideal I-V characteristics in the practical operating range, with an open-circuit voltage of 636 mV, fill factor of 0.79, and AM1 efficiency of 12.6%. A similar epitaxial structure containing no gradient in the n-base showed good solar-cell performance but lower open-circuit voltage (603 mV).

Daiello, R. V.↗