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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 1,081 records · Page 60
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

A study of thermal transitions in a new semicrystalline thermoplastic polyimide

A polyimide derive from 4,4'-isophthaloyl diphthalic anhydride (IDPA) and 1,3-bis (4-aminophenoxy 4'-benzoyl) benzene (1,3-BABB) having semicrystalline behavior was prepared and characterized by differential scanning calorimetry (DSC) and wide angle X-ray scattering (WAXS). Thus a poly(amic acid) film cured in air for one hour each at 100 and 200 C displayed an endotherm at 286 C, followed by a crystallization exotherm at 317 C, and a second melting transition at 350 C. The 286 C melting point appeared to result from earlier solvent-induced crystallization. Films cast from DMAc, air dried, and soaked in methylene chloride could not be induced into semicrystallinity. The fully cured polyimide has a Tg of 216 C. Films heated to temperatures as high as 100 C for one hour in air were transparent and light yellow in color. Those films heated to or above 125 C were translucent. Polarized light microscopy revealed the presence of spherulites 608 micrometers in diameter in a sample cured to 275 C in air. Two film samples, one cured to 275 and the other to 325 C, were evaluated for tensile and ultimate strength, modulus, and percent elongation at 25 and 200 C. These values remained essentially constant at each test temperature.

Pratt, J. Richard↗
NASA NTRS1988

Dendritic growth and structure of undercooled nickel base alloys

The principal objectives of this overall investigation are to: study means for obtaining high undercooling in levitation melted droplets, and study structures produced upon the solidification of these undercooled specimens. Thermal measurements are made of the undercooling, and of the rapid recalescence, to develop an understanding of the solidification mechanism. Comparison of results is made with the modeling studies. Characterization and metallographic work is done to gain an understanding of the relationship between rapid solidification variables and the structures so produced. In ground based work to date, solidification of undercooled Ni-25 wt percent Sn alloy was observed by high-speed cinematography and the results compared with optical temperature measurements. Also in ground based work, high-speed optical temperature measurements were made of the solidification behavior of levitated metal samples within a transparent glass medium. Two undercooled Ni-Sn alloys were examined. Measurements were carried out on samples at undercoolings up to 330 K. Microstructures of samples produced in ground based work were determined by optical metallography and by SEM, and microsegregation by electron microprobe measurements. A series of flight tests were planned to conduct experiments similar to the ground based experiments. The Space Shuttle Columbia carried an alloy undercooled experiment in the STS 61-C mission in January 1986. A sample of Ni-32.5 wt percent Sn eutectic was melted and solidified under microgravity conditions.

Flemings, M. C.↗
NASA NTRS1989

Structural materials for space applications

The long-term performance of structural materials in the space environment is a key research activity within NASA. The primary concerns for materials in low Earth orbit (LEO) are atomic oxygen erosion and space debris impact. Atomic oxygen studies have included both laboratory exposures in atomic oxygen facilities and flight exposures using the Shuttle. Characterization of atomic oxygen interaction with materials has included surface recession rates, residual mechanical properties, optical property measurements, and surface analyses to establish chemical changes. The Long Duration Exposure Facility (LDEF) is scheduled to be retrieved in 1989 and is expected to provide a wealth of data on atomic oxygen erosion in space. Hypervelocity impact studies have been conducted to establish damage mechanisms and changes in mechanical properties. Samples from LDEF will be analyzed to determine the severity of space debris impact on coatings, films, and composites. Spacecraft placed in geosynchronous Earth orbit (GEO) will be subjected to high doses of ionizing radiation which for long term exposures will exceed the damage threshold of many polymeric materials. Radiation interaction with polymers can result in chain scission and/or cross-linking. The formation of low molecular weight products in the epoxy plasticize the matrix at elevated temperatures and embrittle the matrix at low temperatures. This affects both the matrix-dominated mechanical properties and the dimensional stability of the composite. Embrittlement of the matrix at low temperatures results in enhanced matrix microcracking during thermal cycling. Matrix microcracking changes the coefficient of thermal expansion (CTE) of composite laminates and produces permanent length changes. Residual stress calculations were performed to estimate the conditions necessary for microcrack development in unirradiated and irradiated composites. The effects of UV and electron exposure on the optical properties of transparent polymer films were also examined to establish the optimum chemical structure for good radiation resistance. Thoughts on approaches to establishing accelerated testing procedures are discussed.

Tenney, Darrel R.↗
NASA NTRS1989

Ultra-light duct for an anechoic wind tunnel

A tunnel ultra-light (or TUL) is a duct composed of acoustically transparent cloth designed to transform an open-jet wind tunnel into a closed-jet wind tunnel. This concept is of interest (a priori) for anechoic wind tunnels because it improves the aerodynamic quality without hindering the measurement of sound in the far field. A full scale device designed for the 3 m diameter test section of CEPRA 19 was described. The apparatus installation did not develop any significant problems, and the mechanical support turned out to be excellent. Aerodynamic and acoustic tests are discussed. Certain imperfections in the installation as tested - instabilities above 25 m/s and acceptable cloth transmission up to 4kHz were revealed. The system as tested could eventually be used in certain applications, for example, in ground based transport. However, the concept of TUL must be developed further to arrive at a reliable mechanism for use in a large number of applications.

Lambourion, J.↗
NASA NTRS1989

NASA advanced space photovoltaic technology-status, potential and future mission applications

The NASA program in space photovoltaic research and development encompasses a wide range of emerging options for future space power systems, and includes both cell and array technology development. The long range goals are to develop technology capable of achieving 300 W/kg for planar arrays, and 300 W/sq m for concentrator arrays. InP and GaAs planar and concentrator cell technologies are under investigation for their potential high efficiency and good radiation resistance. The Advanced Photovoltaic Solar Array (APSA) program is a near term effort aimed at demonstrating 130 W/kg beginning of life specific power using thin (62 micrometer) silicon cells. It is intended to be technology transparent to future high efficiency cells and provides the baseline for development of the 300 W/kg array.

Flood, Dennis J.↗
NASA NTRS1989

Software package for performing experiments about the convolutionally encoded Voyager 1 link

A software package enabling engineers to conduct experiments to determine the actual performance of long constraint-length convolutional codes over the Voyager 1 communication link directly from the Jet Propulsion Laboratory (JPL) has been developed. Using this software, engineers are able to enter test data from the Laboratory in Pasadena, California. The software encodes the data and then sends the encoded data to a personal computer (PC) at the Goldstone Deep Space Complex (GDSC) over telephone lines. The encoded data are sent to the transmitter by the PC at GDSC. The received data, after being echoed back by Voyager 1, are first sent to the PC at GDSC, and then are sent back to the PC at the Laboratory over telephone lines for decoding and further analysis. All of these operations are fully integrated and are completely automatic. Engineers can control the entire software system from the Laboratory. The software encoder and the hardware decoder interface were developed for other applications, and have been modified appropriately for integration into the system so that their existence is transparent to the users. This software provides: (1) data entry facilities, (2) communication protocol for telephone links, (3) data displaying facilities, (4) integration with the software encoder and the hardware decoder, and (5) control functions.

Cheng, U.↗
NASA NTRS1988

Investigation of stimulated Brillouin scattering switching in mid infrared fibers

Backward stimulated Brillouin scattering (SBS) has been experimentally studied in midinfrared transparent AgCl and KRS-5 fibers. In the present scheme, pump transmission through the fibers and acoustooptic radiative effects are simultaneously observed. The SBS shifted scattered light spectrum is investigated by laser heterodyne spectroscopy using HgCdTe and very fast metal-oxide-metal diode broadband mixers. The results suggest that reflection under high incident laser power departs from simple Fresnel surface reflection.

Yu, Chung↗
NASA NTRS1988

Nonlinear absorption properties of AlGaAs/GaAs multiple quantum wells grown by metalorganic chemical vapor deposition

The nonlinear absorption properties of the excitonic resonances associated with multiple quantum wells (MQWs) in AlGaAs/GaAs grown by metalorganic chemical vapor deposition are reported. The dependence of the saturation properties on growth parameters, especially growth temperature, and the well width are described. The minimum measured saturation intensity for these materials is 250 W/sq cm, the lowest reported value to date. The low saturation intensities are the result of excellent minority carrier properties. A systematic study of minority carrier lifetimes in quantum wells are reported. Lifetimes range from 50-350 ns depending on growth temperature and well width. When corrected for lateral diffusion effects and the measured minority carrier lifetime, the saturation data suggest that saturation intensities as low as 2.3 W/sq cm can be achieved in this system. The first measurements of the dependence of the exciton area and the magnitude of the excitonic absorption on well width are prsented. The growth of MQW structures on transparent GaP substrates is demonstrated and the electroabsorption properties of these structures are reviewed.

Lee, Hsing-Chung↗
NASA NTRS1988

Extraction of topography from side-looking satellite systems - A case study with SPOT simulation data

A simulated data set was used to evaluate techniques for extracting topography from side-looking satellite systems for an area of northwest Washington state. A negative transparency orthophotoquad was digitized at a spacing of 85 microns, resulting in an equivalent ground distance of 9.86 m between pixels and a radiometric resolution of 256 levels. A bilinear interpolation was performed on digital elevation model data to generate elevation data at a 9.86-m resolution. The nominal orbital characteristics and geometry of the SPOT satellite were convoluted with the data to produce simulated panchromatic HRV digital stereo imagery for three different orbital paths and techniques for reconstructing topographic data were developed. Analyses with the simulated HRV data and other data sets show that the method is effective.

Ungar, Stephen G.↗
NASA NTRS1988

Reliable broadcast in hypercube multicomputers

A simple algorithm for broadcasting in a hypercube multicomputer containing faulty nodes/links is proposed. The algorithm delivers multiple copies of the broadcast message through disjoint paths to all the modes in the system. Its salient feature is that the delivery of the multiple copies is transparent to the processes receiving the message and does not require the processes to know the identity of the faulty processors. The processes on nonfaulty nodes that receive the message identify the original message from the multiple copies using some scheme appropriate for the fault model used. The algorithm completes in n + 1 steps if each node can simultaneously use all of its outgoing links. If each node cannot use more than one outgoing link at a time, then the algorithm requires 2n steps.

Ramanathan, P.↗
NASA NTRS1989

IRAS observations of a large sample of normal irregular galaxies

IRAS 12, 25, 60, and 100 micron data are presented for a sample of Irr galaxies which span a large range in star-formation activity. It is found that the dwarf, giant, and amorphous Irr's generally have similar IR properties. The typical L(IR)/L(H-alpha) ratios of most classes of Irr's, except for many of the luminous blue galaxies, are low compared with those of spiral galaxies and are consistent with the Irr's being relatively transparent systems without large amounts of optically hidden star formation. Compared with spiral galaxies, the Irr's have similar L(IR)/L(B) ratios, warmer S(100)/S(60) ratios, cooler S(25)/S(12) ratios, and lower dust-to-H I gas mass ratios. The temperature, dust-to-H I gas mass ratios, and L(IR)/L(B) ratios do not correlate with the metallicity of the ionized gas of the Irr's. A correlation between the IR fluxes and both the H-alpha and the blue stellar fluxes is found for the Irr's.

Hunter, Deidre A.↗
NASA NTRS1988

Soluble and colorless polyimides

Results are reported in the form of reaction diagrams, graphs, and tables of research being conducted to synthesize and characterize linear aromatic polyimides which are soluble in common organic solvents and optically transparent in the 400-600 nm spectral range. These flexible and high-temperature polymeric films and coatings are needed for specific applications on space components such as antennas, solar cells, and thermal control coating systems. Several series of these polyimide films have been produced by making variations in the polymer molecular structure aimed at reducing the electronic interactions between the polymer chains.

St. Clair, Anne K.↗
NASA NTRS1989

Heterogeneous dissemination of projectile materials in the impact melts from Wabar crater, Saudi Arabia

The initial observations of Spencer (1933) that two distinct impact melts coexist at the 90-m-diameter Wabar crater, Saudi Arabia, is confirmed. A dark or 'black' melt contains on the order of 4 percent meteoritic contamination, while the transparent or 'white' melt contains less than 1 percent. The Fe/Ni ratios in both varieties exhibit considerable scatter on electron-microprobe scales, akin to those reported by others for metal spherules in the black melt. If the meteoritic component is subtracted, both melts are chemically very similar. Clasts engulfed by the Wabar melts were investigated also, as they represent the progenitor lithologies from which the melts formed. Bulk compositions for these clasts reveal subtle differences in modal feldspar content within the quartz-rich Wabar target. Both melts require that a minimum of two target lithologies be present in the Wabar melt zone.

Horz, F.↗
NASA NTRS1989

Polyimides containing carbonyl and ether connecting groups - II

In a study of polyimides containing carbonyl and ether connecting groups between aromatic rings, several new polyimides were prepared and characterized. A few of these polymers were semicrystalline. Glass transition temperatures ranged from 164 to 258 C, and crystalline melt temperatures were observed between 350 and 424 C. The semicrystalline polyimide from the reaction of 3.3',4,4'-benzophenonetetracarboxylic dianhydride and 1,3-bis(4-aminophenoxy-4'-benzoyl)benzene provided transparent orange films with excellent tensile properties, exceptional resistance to solvents and strong base, and high thermooxidative stability. In addition, this polyimide provided excellent adhesive strength for joining titanium (6Al-4V) to titanium.

Hergenrother, P. M.↗
NASA NTRS1989

Triton - Do we see to the surface?

The quantity and physical state of methane and nitrogen in the atmosphere of Neptune's satellite Triton and on the surface are evaluated by means of new telescopic data and laboratory measurements of these volatiles. Methane ice is seen in some spectral regions, indicating that the atmosphere is sufficiently transparent to permit sunlight penetration to the surface. Some of the molecular nitrogen absorption occurs in the atmosphere, though some must occur in condensed nitrogen (liquid or solid) on Triton's surface, or in a thin cloud of condensed nitrogen. The Voyager spacecraft cameras should see the surface of Triton.

Cruikshank, D. P.↗
NASA NTRS1989

Thermal infrared (2.5-13.5-micron) spectroscopic remote sensing of igneous rock types on particulate planetary surfaces

The compositional significance of outstanding spectral features in the reflectance spectra of particulate igneous rocks was investigated by analyzing directional reflectance spectra, obtained with an FTIR spectrophotometer at 2.17-13.5 microns, of a suite of well-characterized igneous rocks ground to fine particle size. It was found that, using spectral features associated with the principal Christiansen frequency and with a region of relative transparency between the Si-O stretching and bending bands, it is possible to identify general rock type using the Walter and Salisbury (1989) SCFM chemical index, SCFM, defined as SCFM = SiO2/(SiO2 + CaO + FeO + MgO). It is emphasized, however, that the appearance and the wavelength of these features may be affected by environmental factors.

Salisbury, John W.↗
NASA NTRS1990

Finding Optimal Gains In Linear-Quadratic Control Problems

Analytical method based on Volterra factorization leads to new approximations for optimal control gains in finite-time linear-quadratic control problem of system having infinite number of dimensions. Circumvents need to analyze and solve Riccati equations and provides more transparent connection between dynamics of system and optimal gain.

Milman, Mark H.↗
NASA NTRS1990

Pressure-Measuring Diaphragm Transmits Optical Signals

Proposed sapphire diaphragm performs two functions in instrumented research engine or pressure vessel. Serves both as pressure sensor and as window for observation, optical probing, or optical transmission of other measurements. Deflections of sapphire diaphragm alters resistances of strain gauges mounted around its periphery. At same time, transparent material enables optical measurements of conditions in chamber. Additional information obtained about conditions in chamber without need for additional sensor mounts.

Hill, Arthur J.↗