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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Bit error rate measurement for evaluation of a fiber optic link

Digital fiber-optic data-link terminal modules are being developed in a number of laboratories, and often the modules take the form of black boxes without convenient access to internal signals. This paper discusses types of measurements which can be made using only the digital terminals of the link. Bit-error-rate (BER) vs signal-power data can, of course, provide a means for proving overall link performance, but it can also be used to determine certain internal parameters of the receiver. The theoretical dependence of the BER-vs-light-signal-power curve shape on receiver input-noise equivalent power and comparator slicing level is discussed. BER-vs-light-signal-power measurements obtained with an experimental link are presented and interpreted with the aid of the theoretical curves. The effects of other problems, such as hum or oscillation, on the BER data are mentioned. Sensitivity of the system BER to bit rate is also discussed, with application to determining system operating limits. Since BER measurements are simple to make and can easily be automated, they may prove to be a useful means for either laboratory evaluation or production-line acceptance testing of sealed terminal modules.

Bergman, L. A.↗
NASA NTRS1976

Development of low-cost silicon crystal growth techniques for terrestrial photovoltaic solar energy conversion

Because of the growing need for new sources of electrical energy, photovoltaic solar energy conversion is being developed. Photovoltaic devices are now being produced mainly from silicon wafers obtained from the slicing and polishing of cylindrically shaped single crystal ingots. Inherently high-cost processes now being used must either be eliminated or modified to provide low-cost crystalline silicon. Basic to this pursuit is the development of new or modified methods of crystal growth and, if necessary, crystal cutting. If silicon could be grown in a form requiring no cutting, a significant cost saving would potentially be realized. Therefore, several techniques for growth in the form of ribbons or sheets are being explored. In addition, novel techniques for low-cost ingot growth and cutting are under investigation.

Zoutendyk, J. A.↗
NASA NTRS1978

Adhesive-removal tool

Air-driven hand-held tool with acrylic cutting blade removes adhesives and paint from surfaces. Sidewise-slicing motion of cutter eliminates tendency to "bounce" on resilient materials.

Haynie, C. C.↗
NASA NTRS1979

Process for growing thin polished silicon sheets

Single-crystal sheets pulled from polten silicon floating on refractory melt require no slicing or polishing. Possible materials are chlorides and fluorides of barium, calcium, and strontium. Refractory melt may be able to absorb impurities from silicon and thus obviate postgrowth purification.

Radics, C. C.↗
NASA NTRS1977

Analysis of results of ASTP experiment in electrophoresis

The Apollo-Soyuz Test Project (ASTP) included an electrophoretic separation experiment of biological cells. The nature separation results of aldehyde-fixed rabbit, human and horse red blood cells, which were taken in the form of photographs taken at three-minute intervals, are the subject of this report. The electrophoretic separation was successful in that fractionation according to mobility did occur and was found in the sliced samples. Photographic evidence indicates that the low electroosmotic methylcellulose coating was successful in reducing the electroosmosis to a near zero value. Also, the flight film shows that the bands migrated down the column as theory would predict, producing two bands of high cell concentration separated and surrounded by regions of lower cell concentration. However, most likely some clumping of cells occurred to cause the trailing band to be larger than expected from theory. Overall, the experiment was a success in demonstrating a static electrophoresis separation under microgravity conditions with a resolution not possible on earth.

Vanderhoff, J. W.↗
NASA NTRS1977

The application of LANDSAT-1 imagery for monitoring strip mines in the new river watershed in northeast Tennessee, part 2

The author has identified the following significant results. LANDSAT imagery and supplementary aircraft photography of the New River drainage basin were subjected to a multilevel analysis using conventional photointerpretation methods, densitometric techniques, multispectral analysis, and statistical tests to determine the accuracy of LANDSAT-1 imagery for measuring strip mines of common size. The LANDSAT areas were compared with low altitude measurements. The average accuracy over all the mined land sample areas mapped from LANDSAT-1 was 90%. The discrimination of strip mine subcategories is somewhat limited on LANDSAT imagery. A mine site, whether active or inactive, can be inferred by lack of vegetation, by shape, or image texture. Mine ponds are difficult or impossible to detect because of their small size and turbidity. Unless bordered and contrasted with vegetation, haulage roads are impossible to delineate. Preparation plants and refuge areas are not detectable. Density slicing of LANDSAT band 7 proved most useful in the detection of reclamation progress within the mined areas. For most state requirements for year-round monitoring of surface mined land, LANDSAT is of limited value. However, for periodic updating of regional surface maps, LANDSAT may provide sufficient accuracies for some users.

Shahrokhi, F.↗
NASA NTRS1977

High efficiency thin-film GaAs solar cells

Several oxidation techniques are discussed which have been found to increase the open circuit (V sub oc) of metal-GaAs Schottky barrier solar cells, the oxide chemistry, attempts to measure surface state parameters, the evolving characteristics of the solar cell as background contamination (has been decreased, but not eliminated), results of focused Nd/YAG laser beam recrystallization of Ge films evaporated onto tungsten, and studies of AMOS solar cells fabricated on sliced polycrystalline GaAs wafers. Also discussed are projected materials availability and costs for GaAs thin-film solar cells.

Stirn, R. J.↗
NASA NTRS1977

Digital exploitation of synthetic aperture radar

A digital processing and analysis scheme for use with digitized synthetic aperture radar data was developed. Using data from a four channel system, the imagery is preprocessed using specially designed software and then analyzed using preexisting facilities originally intended for use with MSS type data. Geometric and radiometric correction may be performed if desired, as well as classification analysis, Fast Fourier transform, filtering and level slice and display functions. The system provides low cost output in real time, permitting interactive imagery analysis. System information flow diagrams as well as sample output products are shown.

Wagner, H. L.↗
NASA NTRS1977

On the photographic processing and digital texture for remote sensing of Kujukuri Coast of Chiba in Japan

Remote sensing of various coastal phenomena on the Kujukuri Coast and Kashimanada Coast was done by the use of aircraft for the purpose of investigating the characteristics of shore reefs and floating sand, and the depth of the sea. A multispectral camera and a video ITV camera were used as sensors. The first flight was over the Kashimanada and Kujukuri Coasts and the next flight was over the Katsuura Bay. The shape of shore reefs, the state of floating sand, the depth of the sea, etc., are represented by equidensitographs using texture. The interval of density slices is 0.05. Correlations between the textures represented by equidensitographs, digital graphs and analog display are estimated.

Genda, H.↗
NASA NTRS1977

Digital processing system for developing countries

An effort was undertaken to perform simple digital processing tasks using pre-existing general purpose digital computers. An experimental software package, LIGMALS, was obtained and modified for this purpose. The resulting software permits basic processing tasks to be performed including level slicing, gray mapping and ratio processing. The experience gained in this project indicates a possible direction which may be used by other developing countries to obtain digital processing capabilities.

Nanayakkara, C.↗
NASA NTRS1977

Integration of remote sensing and surface geophysics in the detection of faults

Remote sensing was included in a comprehensive investigation of the use of geophysical techniques to aid in underground mine placement. The primary objective was to detect faults and slumping, features which, due to structural weakness and excess water, cause construction difficulties and safety hazards in mine construction. Preliminary geologic reconnaissance was performed on a potential site for an underground oil shale mine in the Piceance Creek Basin of Colorado. LANDSAT data, black and white aerial photography and 3 cm radar imagery were obtained. LANDSAT data were primarily used in optical imagery and digital tape forms, both of which were analyzed and enhanced by computer techniques. The aerial photography and radar data offered supplemental information. Surface linears in the test area were located and mapped principally from LANDSAT data. A specific, relatively wide, linear pointed directly toward the test site, but did not extend into it. Density slicing, ratioing, and edge enhancement of the LANDSAT data all indicated the existence of this linear. Radar imagery marginally confirmed the linear, while aerial photography did not confirm it.

Jackson, P. L.↗
NASA NTRS1978

Multi-wire slurry wafering demonstrations

Ten slicing demonstrations on a multi-wire slurry saw, made to evaluate the silicon ingot wafering capabilities, reveal that the present sawing capabilities can provide usable wafer area from an ingot 1.05m/kg (e.g. kerf width 0.135 mm and wafer thickness 0.265 mm). Satisfactory surface qualities and excellent yield of silicon wafers were found. One drawback is that the add-on cost of producing water from this saw, as presently used, is considerably higher than other systems being developed for the low-cost silicon solar array project (LSSA), primarily because the saw uses a large quantity of wire. The add-on cost can be significantly reduced by extending the wire life and/or by rescue of properly plated wire to restore the diameter.

Chen, C. P.↗
NASA NTRS1978

Impact behavior of filament wound graphite/epoxy fan blades

The fabrication and impact tests of graphite/epoxy filament wound fan blades are discussed. Blades which were spin tested at tip speeds up to 305 meters per second retained their structural integrity. Two blades were each impacted with a 454 gram slice of a 908 gram simulated bird at a tip speed of 263 meters per second and impact angles of 22 and 32 deg. The impact tests were recorded with high-speed movie film. The blade which was impacted at 22 deg sustained some root delamination but remained intact. The 32 deg impact separated the blade from the root. No local damage other than leading edge debonding was observed for either blade. Results of a failure mode analysis are also discussed.

Bowles, K. J.↗
NASA NTRS1977

Laser-zone growth in a Ribbon-To-Ribbon (RTR) process. Silicon sheet growth development for the large area silicon sheet task of the low cost silicon solar array project

The Ribbon-to-Ribbon (RTR) approach to silicon ribbon growth is investigated. An existing RTR apparatus is to be upgraded to its full capabilities and operated routinely to investigate and optimize the effects of various growth parameters on growth results. A new RTR apparatus was constructed to incorporate increased capabilities and improvements over the first apparatus and to be capable of continuous growth. New high power lasers were implemented and this led to major improvements in growth velocity -- 4 inch/min. growth has been demonstrated. A major step in demonstration of the full feasibility of the RTR process is reported in the demonstration of RTR growth from CVD polyribbon rather than sliced polyribbon ingots. Average solar cell efficiencies of greater than 9% and a best cell efficiency of 11.7% are reported. Processing was shown to provide a substantial improvement in material minority carrier diffusion length. An economic analysis is reported which treats both the polyribbon fabrication and RTR processes.

Gurtler, R. W.↗
NASA NTRS1978

Development of an improved high efficiency thin silicon solar cell

Efforts were concerned with optimizing techniques for thinning silicon slices in NaOH etches, initial investigations of surface texturing, variation of furnace treatments to improve cell efficiency, initial efforts on optimization of gridline and cell sizes and Pilot Line fabrication of quantities of 2 cm x 2 cm 50 micron thick cells.

Lindmayer, J.↗
NASA NTRS1976

A new lightweight solar cell

Highly reproducible, very thin (40-80 microns thick) silicon solar cells are examined. These cells are the product of silicon thinning techniques that produce very flexible, resilient slices as compared to other techniques. Measurements on solar cells 2 cm by 2 cm by 50 microns thick producing 60 mW or more at AM0 are described. These cells have fine-line metallizations, tantalum oxide antireflection coatings and back-surface aluminum alloy.

Lindmayer, J.↗
NASA NTRS1976

Single crystal and polycrystalline GaAs solar cells using AMOS technology

A description is given of current technology for fabricating single AMOS (antireflection-coated metal oxide semiconductor) solar cells, with attention given to thermal, plasma, and anodic oxidation, native oxide stripping, and X-ray photoelectron spectroscopy results. Some preliminary results are presented on the chemistry and electrical characterization of such cells, and the characteristics of cells fabricated on sliced polycrystalline GaAs wafers are examined. Consideration is also given to the recrystallization of evaporated Ge films for use as low-cost substrates for polycrystalline GaAs solar cells.

Stirn, R. J.↗
NASA NTRS1977

Zn diffusion in Al/0.7/Ga/0.3/As compared with that in GaAs

Zinc was diffused into 4 times 10 to the 17th per cu cm n-type Al(0.7)Ga(0.3)As grown by liquid-phase epitaxy and also into n-type 2 times 10 to the 17th per cu cm doped GaAs slices at 600, 650, and 750 C. The Zn diffusion coefficient in the Al(0.7)Ga(0.3)As was about one order of magnitude larger than in GaAs. The significance of this fact is that diffusion of Zn through a 0.5 micron Al(0.7)Ga(0.3)As layer appears to be possible with adequate control of the junction depth in the underlying GaAs.

Flat, A.↗