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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 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Two-electron bond-orbital model, 2

The two-electron bond-orbital model of tetrahedrally-coordinated solids is generalized and its application extended. All intrabond matrix elements entering the formalism are explicitly retained, including the direct overlap S between the anion and cation sp3 hybrid wavefunctions. Complete analytic results are obtained for the six two-electron eigenvalues and eigenstates of the anion-cation bond in terms of S, one-electron parameters V2 and V3, and two-electron correlation parameters V4, V5 and V6. Refined formulas for the dielectric constant and the nuclear exchange and pseudodipolar coefficients, as well as new expressions for the valence electron density, polarity of the bond and the cohesive energy, are then derived. The theory gives a good account of the experimentally observed trends in all properties considered and approximate quantitative agreement is achieved for the pseudodipolar coefficient.

Huang, C.↗
NASA NTRS1976

Tracker implementation for the orbiter Ku-band communications antenna

Possible implementations and recommendations for the Space Shuttle Ku-Band integrated communications/radar antenna tracking system were evaluated. Communication aspects involving the Tracking Data Relay Satellite (TDRS)/Orbiter Ku-Band link are emphasized. Detailed analysis of antenna sizes, gains and signal-to-noise ratios shows the desirability of using maximum size 36-inch diameter dish and a triple channel monopulse. The use of the original baselined 20 inch dish is found to result in excessive acquisition time since the despread signal would be used in the tracking loop. An evaluation of scan procedures which includes vehicle dynamics, designation error, time for acquisition and probability of acquisition shows that the conical scan is preferred since the time for lock-on for relatively slow look angle rates will be significantly shorter than the raster scan. Significant improvement in spherical coverage may be obtained by reorienting the antenna gimbal to obtain maximum blockage overlap.

Rudnicki, J. F.↗
NASA NTRS1975

A grid of model atmospheres for metal-deficient giant stars. I

A grid of flux-constant model atmospheres for stars with effective temperatures between 3750 and 6000 K, log g between 0.75 and 3.0, and (A/H) between -3.0 and 0.0 has been constructed. The line absorption is approximated by opacity distribution functions. Metal lines and molecular lines, including those from the infrared bands of CO and CN, are taken into account. The variation of the structure of the models with metal abundance and microturbulence parameter is found to be quite regular and not very drastic. The surface cooling produced by CO is important for all the models with a maximum temperature of 5000 K, while CN mainly causes a backwarming effect but is not very important for solar CNO abundances. The effects of convection, estimated by using the mixing-length approximation, are important only for the coldest models. The models compare very well with models from overlapping regions of other grids. A solar model consistent with the grid models is found to agree satisfactorily with empirical solar model atmospheres. The careful use of scaled solar models for stars with (A/H) approximately equal to zero is justified.

Gustafsson, B.↗
NASA NTRS1975

Scanning electron microscope investigation of the structural growth in thick sputtered coatings

Sputtered S-Monel, silver, and 304 stainless steel coatings and molybdenum disulfide coatings were deposited on mica and metal substrates with various surface finishes to investigate the structural growth of the coating by scanning electron microscopy. The geometry and the surface morphology of the nodules are characterized. Compositional changes within the coating were analyzed by energy dispersive X-ray analysis. Defects in the surface finish act as preferential nucleation sites and form isolated overlapping and complex nodules and various unusual surface overgrowths on the coating. The nodule boundaries are very vulnerable to chemical etching and these nodules do not disappear after full annealing. Further, they have undesirable effects on mechanical properties; cracks are initiated at the nodules when the coating is stressed by mechanical forces.

Spalvins, T.↗
NASA NTRS1975

On the source of lunar limb compressions

Magnetic-field measurements made on board the Apollo 15 and 16 subsatellites in low-altitude lunar orbit are used to study compressions of the magnetic field over terminator regions when the moon is in the solar wind. These compressional disturbances occur at just in front of the terminator, but only when specific selenographic regions appear at the lunar limb. The occurrence rate, strength, and position of the compression relative to the limb are different for each source region. Where overlaps of limb-compression occurrence statistics and lunar magnetic-field maps exist, the limb-compression occurrence rates have a high degree of correlation with magnetic-field strength. Thus the most probable cause of limb compressions is deflection of the solar wind by the lunar surface magnetic field as the solar wind flows past the lunar terminators.

Russell, C. T.↗
NASA NTRS1975

Looking forward to the present

The present understanding of the origin of life based on Oparin's (1924) conception of life as a manifestation of matter in a special stage of its development is outlined. The results of chemical analyses of lunar samples are discussed, and their implications regarding chemical reactions beginning with carbonaceous dust are considered. Amino acids isolated from lunar samples taken from different sites show a high degree of similarity, in agreement with the hypothesis that carbon compounds, including amino acid precursors, were implanted on the lunar surface by components of the solar wind. The amino acid precursors are most likely a cyanide compound. Overlapping amino acid/carbon ratios from lunar samples and samples of meteorites suggest a common cosmochemical state of carbon in the solar system.

Fox, S. W.↗
NASA NTRS1976

Comparisons of measured and theoretical thermospheric daily composition variations

A comparison of the diurnal component of the daily variation in the neutral composition data from the San Marco 3 Nace (Neutral Atmospheric Composition Experiment) mass spectrometer at 220, 250, and 280 km, the OGO-6 model data at 450 km, rocket measurements of nitrogen between 140 and 300 km, and the two-constituent theoretical model of Mayr and Volland (1973) gives good agreement for molecular nitrogen and atomic oxygen. The Nace and rocket measurements overlap in altitude, and there is good agreement in the amplitude and phase of the diurnal and semidiurnal components for molecular nitrogen. The helium diurnal amplitude and phase of the theoretical model are in fair agreement with the Nace results, while the amplitude from the OGO-6 model at 450 km is much larger than the model predicts, a result suggesting that the OGO-6 model diurnal amplitude may be overestimated as the result of an incomplete separation of local-time and seasonal effects.

Kasprzak, W. T.↗
NASA NTRS1976

Lunar radargrammetry with ALSE-VHF imagery

Results are presented for a controlled experiment with a pair of overlapping lunar ALSE-VHF images produced in two consecutive revolutions of the Apollo command module around the moon. A theoretical treatment is presented of the mathematical tools for ALSE radargrammetry. Evaluation of radargrammetric mapping with single strips and a radar stereo model led to preliminary results in a test area around Mons Maraldi. Accuracy achieved with single radar images was about plus or minus 250 m along track and plus or minus 500 m across track. Stereoradargrammetry was used to generate a contour plot of Mons Maraldi and to evaluate the overall height accuracy obtainable from ALSE radar. About plus or minus 120 m of accuracy is obtained if the stereo model is corrected using a few control points. This makes ALSE stereo radar heights competitive with or even superior to vidicon data obtained for planetary exploration. The present basic limitation to radargrammetric accuracy from ALSE-VHF images is the identifiability of surface features.

Leberl, F.↗
NASA NTRS1976

Radiative transfer within the earth's troposphere and stratosphere - A simplified radiative-convective model

A radiative transfer model of the troposphere and stratosphere is presented which includes both long-wave cooling and solar heating due to H2O, CO2 and O3 and has a simplified formulation which facilitates the inclusion of Doppler broadening, H2O continuum bands, hot and minor isotopic bands of CO2, and overlap of H2O bands with CO2 and O3 bands. The radiative model is used to develop an accurate radiative-convective model for studying the global surface temperature, stratospheric thermal structure and the net outgoing long-wave flux.

Ramanathan, V.↗
NASA NTRS1976

Side-looking radar mosaicking experiment

A block of 24 overlapping synthetic aperture side-looking radar images flown over a well mapped area of about 90,000 sq km provided an opportunity to evaluate the mapping accuracy achieved in current radar mosaicking projects. The maps of scale 1:24,000 that are available in the imaged area permitted the study of the geometric errors of the radar mosaics and of individual radar strips. An estimate was obtained for the effect of the distribution and density of ground control points and for the accuracy of different mosaicking methods that are currently employed with synthetic aperture radar images. It is shown that a successful radar mosaicking process requires the elimination of image errors of up to several kilometers. These errors are introduced as a result of the limited precision of the inertial aircraft navigation. An example of a radar mapping effort in which the navigation errors could be eliminated is presented. The resulting radar mosaics have residual RMS mapping errors of planimetry of about plus or minus 150 m.

Leberl, F.↗
NASA NTRS1976

Atmospheric neutrons

Additional calibrations of the University of California double-scatter neutron detector and additional analysis corrections lead to slightly changed neutron fluxes. The theoretical angular distributions of Merker (1975) are in general agreement with the reported experimental fluxes but do not give the peaks for vertical upward and downward moving neutrons. The theoretical neutron escape current is in agreement with the experimental values from 10 to 100 MeV. The experimental fluxes obtained agree with those of Kanbach et al. (1974) in the overlap region from 70 to 100 MeV.

Preszler, A. M.↗
NASA NTRS1976

Spectral properties of hydrogen, helium, methane, and ammonia at thermal infrared wavelengths

The paper presents some results of a theoretical and laboratory program to determine the thermal infrared spectral properties of the principal gaseous constituents of the atmosphere of Jupiter. Birnbaum (1975) has measured laboratory spectra in the 16- to 1000-micron wavelength range for hydrogen and hydrogen-helium mixtures at Jovian temperatures. These are compared with theoretically computed spectra in order to determine the temperature dependence of the line strengths in the pressure-induced rotational band and the overlap parameters from the translational band. Existing spectral data for methane do not agree well with measurements of the nu 4 band at room temperature. A revised allocation of line intensities is proposed. Existing data for the nu 2 (10-micron) band of ammonia agree reasonably well with measurements at room temperature and at -77 C, but there are some important discrepancies which remain to be explained.

Taylor, F. W.↗
NASA NTRS1977

Uniform spray coating for large tanks

System employs spray facility located within ventilated plastic booth to uniformly coat exterior of large cylindrical tanks with polyurethane foam insulation. Coating target is rotated on turntable while movable spray guns apply overlapping spirals of foam. Entire operation may be controlled by single operator from remote station.

Carter, J. M.↗
NASA NTRS1976

Linear charge coupled device detector array for imaging light propagating in an integrated thin-film optical waveguide

Device design, fabrication, and operation of a linear charge coupled device (CCD) detector array integrated with a thin film optical waveguide and applications of this structure to integrated optical signal processing and fiber optical communications were discussed. A two phase, overlapping-gate CCD is connected in parallel by means of a series of gates to an array of photodiodes. The photodiode provides an electrode free surface region so that a highly efficient waveguide detector coupling technique can be implemented. A thermally-oxidized layer of SiO2 forms an effective substrate for the optical waveguide.

Chen, C. L.↗
NASA NTRS1976

Pressure model of a four-way spool valve for simulating electrohydraulic control systems

An equation that relates the pressure flow characteristics of hydraulic spool valves was developed. The dependent variable is valve output pressure, and the independent variables are spool position and flow. This causal form of equation is preferred in applications that simulate the effects of hydraulic line dynamics. Results from this equation are compared with those from the conventional valve equation, whose dependent variable is flow. A computer program of the valve equations includes spool stops, leakage spool clearances, and dead-zone characteristics of overlap spools.

Gebben, V. D.↗
NASA NTRS1975

Simulation of Thematic Mapper performance as a function of sensor scanning parameters

The investigation and results of the Thematic Mapper Instrument Performance Study are described. The Thematic Mapper is the advanced multispectral scanner initially planned for the Earth Observation Satellite and now planned for LANDSAT D. The use of existing digital airborne scanner data obtained with the Modular Multispectral Scanner (M2S) at Bendix provided an opportunity to simulate the effects of variation of design parameters of the Thematic Mapper. Analysis and processing of this data on the Bendix Multispectral Data Analysis System were used to empirically determine categorization performance on data generated with variations of the sampling period and scan overlap parameters of the Thematic Mapper. The Bendix M2S data, with a 2.5 milliradian instantaneous field of view and a spatial resolution (pixel size) of 10-m from 13,000 ft altitude, allowed a direct simulation of Thematic Mapper data with a 30-m resolution. The flight data chosen were obtained on 30 June 1973 over agricultural test sites in Indiana.

Johnson, R. H.↗
NASA NTRS1974

Techniques for delineation and portrayal of land cover types using ERTS-1 data

The author has identified the following significant results. ERTS data was used to map land cover in agricultural areas, although in some parts of Pennsylvania, with small irregular fields, many of the pixels overlap field boundaries and cause difficulties in classification. Various techniques and devices were used to display the results of these land cover analyses. The most promising approach would be a user-interactive color monitor interfaced with a large computer so that classification results could be displayed on the CRT and these results output by a hard complete copier.

Mcmurtry, G. J.↗
NASA NTRS1977

Analysis of diffential absorption lidar technique for measurements of anhydrous hydrogen chloride from solid rocket motors using a deuterium fluoride laser

An active optical technique (differential absorption lidar (DIAL)) for detecting, ranging, and quantifying the concentration of anhydrous HCl contained in the ground cloud emitted by solid rocket motors (SRM) is evaluated. Results are presented of an experiment in which absorption coefficients of HCl were measured for several deuterium fluoride (DF) laser transitions demonstrating for the first time that a close overlap exists between the 2-1 P(3) vibrational transition of the DF laser and the 1-0 P(6) absorption line of HCl, with an absorption coefficient of 5.64 (atm-cm) to the -1 power. These measurements show that the DF laser can be an appropriate radiation source for detecting HCl in a DIAL technique. Development of a mathematical computer model to predict the sensitivity of DIAL for detecting anhydrous HCl in the ground cloud is outlined, and results that assume a commercially available DF laser as the radiation source are presented.

Bair, C. H.↗