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At least 235 records · Page 13

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NASA NTRS1980

Silicon ribbon growth using scanned lasers

The recent demand for low-cost photovoltaic arrays has renewed the interest in growing silicon in ribbon form. The approach used in the present paper for the growth of low-cost silicon ribbon is shown schematically. A pair of scanned, focused CO2 laser beams is directed onto both sides of a preformed silicon ribbon. A narrow (about 1 mm high) molten zone is formed across the full width of the ribbon. As the silicon ribbon is passed through the laser-heated zone, large grains are produced in the recrystallized ribbon. The laser beam path is outlined schematically. As a general rule, the lenses are not positioned so as to bring the laser beams to a fine focus, since highly focused beams would vaporize the silicon surface rather than serve to melt the bulk. Silicon ribbon has been grown at rates up to 13.3 cm/min by this approach. The best solar cell fabricated so far on this material has a conversion efficiency of 12.7%.

Baghdadi, A.↗

NASA NTRS1980

Installing fiber insulation

A method for installing fragile, high temperature insulation batting in an elongated cavity or in a resilient wire sleeve to form a resilient seal. The batting is preformed to rough dimensions and wrapped in a plastic film, the film being of a material which is fugitive at a high temperature. The film is heat sealed and trimmed to form a snugly fit skin which overlaps at least at one end to permit attachment of a pull cord. The film absorbs the tensile force of pulling the film enclosed batting through the cavity or wire mesh sleeve and is subsequently driven off by high temperature baking, leaving only the insulation in the cavity or wire mesh sleeve.

Wang, D. S.↗

NASA NTRS1981

High-current, fast-switching transistor development

The design, wafer-processing techniques, and various measurements which include forward safe operating area, dc characteristics, and switching times are described for a larger-diameter (33) transistor. An improved base contact for equalizing the base-emitter voltage at high currents was developed along with an improved emitter contact preform which increases the silicon area available for current conduction. The electrical performance achieved is consistent with the proposed optimum design.

Hower, P. L.↗

NASA NTRS1982

Integral throat entrance development, qualification and production for the Antares 3 nozzle

Although design analyses of a G-90 graphite integral throat entrance for the Antares 3 solid rocket motor nozzle indicated acceptable margins of safety, the nozzle throat insert suffered a thermostructural failure during the first development firing. Subsequent re-analysis using properties measured on material from the same billet as the nozzle throat insert showed negative margins. Carbon-carbon was investigated and found to result in large positive margins of safety. The G-90 graphite was replaced by SAI fast processed 4-D material which uses Hercules HM 10000 fiber as the reinforcement. Its construction allows powder filling of the interstices after preform fabrication which accelerates the densification process. Allied 15V coal tar pitch is then used to complete densification. The properties were extensively characterized on this material and six nozzles were subjected to demonstration, development and qualification firings.

Clayton, F. I.↗

NASA NTRS1982

Preliminary design notes on a low F-number EMR

Conceptual design studies were completed on a new Electrostatic Membrane Reflector, EMR. This new model incorporates both a preformed, curved membrane reflector and membrane control surface. This improved model is the second step toward a high precision large space antenna that could eventually exhibit a performance in terms of aperture diameter to surface quality exceeding 1,000,000. Design trades indicate that the goal of a low ratio of focal length to aperture diameter (f sub n) can be achieved while operating in a humid sea-level environment. A nominal surface quality of 1.0 mm (RMS) is possible using available off-the-shelf commercial membranes. Both the membrane reflector and control electrode surface are fabricated from 12 gore segments and attached to the available 12 sided, 4.88 m diameter rim. The preferred conceptual design has a f sub n = 1.0. The 4.88 m aperture is performed with a centerline displacement of 0.306 m. The nominal spacing between the membrane reflector and the electrode control surface is 50.8 mm. The centerline membrane displacement from its performed to its tensioned, smooth shape is about 3 mm. The membrane tensioning is achieved by application of an electrostatic pressure of 2.6 N/sq cm and a voltage of about 38 kV.

Mihora, D. J.↗

NASA NTRS1982

Time-resolved spectroscopy of solid poly/1-vinyl naphthalene/ following electron beam pulse radiolysis - Pulse radiolytic studies on polymers

Transient emission studies following pulse radiolysis of solid poly(1-vinyl naphthalene) show existence of excited monomers and two excimers. Quenching experiments indicate that excimers are not formed directly by recombination of ions but probably by trapping of migrating monomeric excitation in preformed traps whose density is approximately one in 1000.

Coulter, D. R.↗

NASA NTRS1983

High Power Switching Transistor

Improved switching transistors handle 400-A peak currents and up to 1,200 V. Using large diameter silicon wafers with twice effective area as D60T, form basis for D7 family of power switching transistors. Package includes npn wafer, emitter preform, and base-contact insert. Applications are: 25to 50-kilowatt high-frequency dc/dc inverters, VSCF converters, and motor controllers for electrical vehicles.

Hower, P. L.↗

NASA NTRS1983

Off-Design Turbine Modeling

Off-design efficiency and flow function obtained from design point input data. Computer program PART improved method of representing turbine component when preforming calculations of off-design-point data to total efficiency over range of pressure ratios and speeds specified by user. PART written in FORTRAN IV.

Converse, G. L.↗

NASA NTRS1982

Test and analysis of Celion 3000/PMR-15, graphite/polyimide bonded composite joints: Data report

Standard single lap, double lap and symmetric step lap bonded joints of Celion 3000/PMR-15 graphite/polyimide composite were evaluated. Composite to composite and composite to titanium joints were tested at 116 K (-250 F), 294 K (70 F) and 561 K (550 F). Joint parameters evaluated are lap length, adherend thickness, adherend axial stiffness, lamina stacking sequence and adherend tapering. Advanced joint concepts were examined to establish the change in performance of preformed adherends, scalloped adherends and hybrid systems. The material properties of the high temperature adhesive, designated A7F, used for bonding were established. The bonded joint tests resulted in interlaminar shear or peel failures of the composite and there were very few adhesive failures. Average test results agree with expected performance trends for the various test parameters. Results of finite element analyses and of test/analysis correlations are also presented.

Cushman, J. B.↗

NASA NTRS1983

Test and analysis of Celion 3000/PMR-15, graphite/polyimide bonded composite joints: Summary

Standard single lap, double lap and symmetric step lap bonded joints of Celion 3000/PMR-15 graphite/polyimide composite were evaluated. Composite to composite and composite to titanium joints were tested at 116K (-250 F), 294K (70 F) and 561K (550 F). Joint parameters evaluated were lap length, adherend thickness, adherend axial stiffness, lamina stacking sequence and adherend tapering. Tests of advanced joint concepts were also conducted to establish the change in performance of preformed adherends, scalloped adherends and hybrid systems. Special tests were conducted to establish material properties of the high temperature adhesive, designated A7F, used for bonding. Most of the bonded joint tests resulted in interlaminar shear or peel failures of the composite. There were very few adhesive failures. Average test results agree with expected performance trends for the various test parameters. Results of finite element analyses and of test/analysis correlations are also presented.

Cushman, J. B.↗

NASA NTRS1983

Sphere forming method and apparatus

A system is provided for forming small accurately spherical objects. Preformed largely spherical objects are supported at the opening of a conduit on the update of hot gas emitted from the opening, so the object is in a molten state. The conduit is suddenly jerked away at a downward incline, to allow the molten object to drop in free fall, so that surface tension forms a precise sphere. The conduit portion that has the opening, lies in a moderate vacuum chamber, and the falling sphere passes through the chamber and through a briefly opened valve into a tall drop tower that contains a lower pressure, to allow the sphere to cool without deformation caused by falling through air.

Youngberg, C. L.↗

NASA NTRS1984

Real-time synthetic aperture radar processing

Real-time acousto-optic SAR processors are described and experimentally demonstrated. SAR imaging is performed in one of the architectures by applying the signal to an acousto-optic device and correlating it with chirp signals recorded on an optical transparency by time integration on a CCD detector. In a different implementation, the imaging is preformed by interfering the light beams diffracted from two separate acousto-optic devices, one modulated the radar signal and the second by the reference chirp waveform.

Psaltis, D.↗

NASA NTRS1981

Energy efficient engine. Volume 2. Appendix A: Component development and integration program

The large size and the requirement for precise lightening cavities in a considerable portion of the titanium fan blades necessitated the development of a new manufacturing method. The approach which was selected for development incorporated several technologies including HIP diffusion bonding of titanium sheet laminates containing removable cores and isothermal forging of the blade form. The technology bases established in HIP/DB for composite blades and in isothermal forging for fan blades were applicable for development of the manufacturing process. The process techniques and parameters for producing and inspecting the cored diffusion bonded titanium laminate blade preform were established. The method was demonstrated with the production of twelve hollow simulated blade shapes for evaluation. Evaluations of the critical experiments conducted to establish procedures to produce hollow structures by a laminate/core/diffusion bonding approach are included. In addition the transfer of this technology to produce a hollow fan blade is discussed.

Moracz, D. J.↗

NASA NTRS1984

Data appendix: F-number=1.0 EMR with a flexible back electrode

A 12.5 micron Tedlar low f-number electrostatic membrane reflector was tested. The antenna reflector was designed to achieve a spherical reflector surface with a focal length to diameter ratio f(sub n) of one and a potential accuracy of 1.0 over its 4.88 m diameter. The configuration required the cutting and joining of twelve pie-shaped panels to form the reflector surface. Electrostatic forces are used to tension this preformed membrane reflector. The test data is spare-only three sets of measurements were taken due to lack of funds.

Mihora, D. J.↗

NASA NTRS1986

Wrinkle-Free Hydroforming of Wire Mesh

Plastic films lubricate workpiece so it deforms smoothly. Thin layers of plastic below top die and above bottom die ensure wire screen slides as shaped by hydroforming. Plastic layers are 0.0043 in. (0.11 m) thick. Preformed to contours of dies and final workpiece. New method of hydroforming fine-wire-mesh heat-shield screens eliminates wrinkles and marks. Prevents screen from being damaged and pores from becoming blocked.

Fadness, J.↗

NASA NTRS1985

Evaluation of a high temperature adhesive for fabricating graphite/PMR-15 polyimide structures

Tests are conducted to measure shear strength, shear modulus and flatwise tensile strength of the A7F (amide-imide modified LARC-13) adhesive system. An investigation is also conducted to determine the effect of geometric material parameters, and elevated temperature on the static strength of standard joints. Single-lap and double-lap composite joints, and single, double and step lap composite to metal joints are characterized. A series of advanced joints consisting of preformed adherends, adherends with scalloped edges and joints with hybrid interface plies are tested and compared to baseline single and double-lap designs.

Hill, S. G.↗

NASA NTRS1986

Molecular replication

The object of our research program is to understand how polynucleotide replication originated on the primitive Earth. This is a central issue in studies of the origins of life, since a process similar to modern DNA and RNA synthesis is likely to have formed the basis for the most primitive system of genetic information transfer. The major conclusion of studies so far is that a preformed polynucleotide template under many different experimental conditions will facilitate the synthesis of a new oligonucleotide with a sequence complementary to that of the template. It has been shown, for example, that poly(C) facilitates the synthesis of long oligo(G)s and that the short template CCGCC facilities the synthesis of its complement GGCGG. Very recently we have shown that template-directed synthesis is not limited to the standard oligonucleotide substrates. Nucleic acid-like molecules with a pyrophosphate group replacing the phosphate of the standard nucleic acid backbone are readily synthesized from deoxynucleotide 3'-5'-diphosphates on appropriate templates.

Orgel, L. E.↗

NASA NTRS1985

Changes in atmospheric CO2 - Factors regulating the glacial to interglacial transition

Observations of pCO2 and delta-C-13 for the deep sea, and delta-C-13 for shallow waters, furnish important constraints on the chemistry of the glacial ocean. The concentration of preformed nutrients in the model presented reflects the concentration of nitrogen at depth, the efficiency with which nitrogen is supplied to the cold surface water by exchange with the intermediate layer, the extent to which nutrients in the cold surface regime are diluted by low nutrient water from lower latitude, and the efficiency with which nutrients are used up by the local cold water biota.

Ennever, F. K.↗