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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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NASA NTRS1975

Effect of various material properties on the adhesive stage of fretting

Various properties of metals and alloys have been studied with respect to their effect on the initial stage of the fretting process, namely adhesion. Crystallographic orientation, crystal structure, interfacial binding energies of dissimiliar metal, segregation of alloy constituents and the nature and structure of surface films have all been found to influence adhesion. High atomic density, low surface energy grain orientations exhibit lower adhesion than other orientations. Hexagonal metals in general manifest less adhesive wear than cubic metal. Knowledge of interfacial surface binding energies can assist in predicting adhesive transfer and wear. Selective surface segregation of alloy constituents can accomplish both a reduction in adhesion and improved surface oxidation characteristics. Equivalent surface coverages of various adsorbed species indicate that some are markedly more effective in inhibiting adhesion than others.

Buckley, D. H.↗

NASA NTRS1974

Effect of various material properties on the adhesive stage of fretting

Buckley, D. H.↗

NASA NTRS1976

The first Viking mission to Mars

The paper outlines the major goals and present achievements of the Viking 1 mission to Mars. The construction and instrumentation of the orbiter and lander are described. The criteria used to select the optimum landing site are discussed together with orbit adjustments and the landing process. Special attention is given to constraints on surface coverage and observation conditions.

Soffen, G. A.↗

NASA NTRS1977

Phobos and Deimos - Geodesy

Results of geodesy studies of Phobos and Deimos based on Mariner 9 imaging data are presented. This analysis includes a review of the surface coverage and high resolution pictures obtained and the determined sizes, shapes, topographies, and librations of the two Martian satellites. Also, exploration of Phobos and Deimos by missions such as Viking is discussed.

Duxbury, T. C.↗

NASA NTRS1977

An introduction to orbit dynamics and its application to satellite-based earth monitoring systems

The long term behavior of satellites is studied at a level of complexity suitable for the initial planning phases of earth monitoring missions. First-order perturbation theory is used to describe in detail the basic orbit dynamics of satellite motion around the earth and relative to the sun. Surface coverage capabilities of satellite orbits are examined. Several examples of simulated observation and monitoring missions are given to illustrate representative applications of the theory. The examples stress the need for devising ways of maximizing total mission output in order to make the best possible use of the resultant data base as input to those large-scale, long-term earth monitoring activities which can best justify the use of satellite systems.

Brooks, D. R.↗

NASA NTRS1978

Interaction of hydrogen chloride with alumina

The influence of temperature, pressure, and outgas conditions on the absorption of hydrogen chloride and water vapor on both alpha and gamma alumina was studied. Characterization of the adsorbents was performed using X-ray powder diffraction, scanning electron microscopy (SEM), low temperature nitrogen adsorption desorption measurements, BET nitrogen surface area measurements and electron spectroscopy for chemical analysis (ESCA). Water vapor adsorption isotherms at 30, 40, and 50 C were measured on alpha and gamma alumina after outgassing at 80, 200, and 400 C. Both outgas temperature and adsorption temperature influenced the adsorption of water vapor on the aluminas. The water vapor adsorption was completely reversible. Alpha alumina absorbed more water per unit area than gamma alumina. Differences in the adsorption capacity for water vapor of the two aluminas were explained on the basis of ideal surface models of alpha and gamma alumina. Isosteric heats of adsorption for water vapor on the aluminas were determined over a limited range of surface coverage.

Bailey, R. R.↗

NASA NTRS1978

Effect of oxygen, methyl mercaptan, and methyl chloride on friction behavior of copper-iron contacts

Sliding friction experiments were conducted with an iron rider on a copper disk and a copper rider on an iron disk. The sputter cleaned iron and copper disk surfaces were saturated with oxygen, methyl mercaptan, and methyl chloride at atmospheric pressure. Auger emission spectroscopy was used to monitor the surfaces. Lower friction was obtained in all experiments with the copper rider sliding on the iron disk than when the couple was reversed. For both iron and copper disks, methyl mercaptan gave the best surface coverage and was most effective in reducing friction. For both iron and copper disks, methyl chloride was the least effective in reducing friction. With sliding, copper transferred to iron and iron to copper.

Buckley, D. H.↗

NASA NTRS1979

Synthesis of regional crust and upper-mantle structure from seismic and gravity data

Available seismic and ground based gravity data are combined to infer the three dimensional crust and upper mantle structure in selected regions. This synthesis and interpretation proceeds from large-scale average models suitable for early comparison with high-altitude satellite potential field data to more detailed delineation of structural boundaries and other variations that may be significant in natural resource assessment. Seismic and ground based gravity data are the primary focal point, but other relevant information (e.g. magnetic field, heat flow, Landsat imagery, geodetic leveling, and natural resources maps) is used to constrain the structure inferred and to assist in defining structural domains and boundaries. The seismic data consists of regional refraction lines, limited reflection coverage, surface wave dispersion, teleseismic P and S wave delay times, anelastic absorption, and regional seismicity patterns. The gravity data base consists of available point gravity determinations for the areas considered.

Alexander, S. S.↗

NASA NTRS1982

Topoclimatological survey of Switzerland

The application of Heat Capacity Mapping Mission data to subsynoptic climate analysis of Switzerland was examined. The data included the surface temperature distributions of urban heat islands and the Swiss Alps. Analog and digital data evaluation procedures are described as well as the ground truth acquisition and comparison program. The dependence of the temperature distributions on topography and surface coverage types is assessed. The results indicate that air temperature inversion zones are detectable.

Winiger, M.↗

NASA NTRS1983

Outer atmospheres of cool stars. XV - High-dispersion ultraviolet studies of active chromosphere G-K dwarfs

IUE ultraviolet echelle spectra of three late-type active chromosphere dwarf stars, Chi-1 Orionis, Xi Bootis, and Epsilon Eridani, are compared with previously published observations of the quiet chromosphere dwarfs Alpha Centauri A and Alpha Centauri B. The spectra indicate a gross strengthening of chromospheric and transition-region line fluxes from quiet to active dwarf stars without a fundamental change in their line shapes. Qualitatively the same spectroscopic behavior is seen in detail on the solar surface between regions of strong and weak magnetic fields. It is argued that the correspondence between the stellar and solar behavior is not accidental, but instead affirms that enhanced chromospheric and coronal emission on late-type main sequence stars is a result of increased surface coverage of magnetic active regions.

Ayres, T. R.↗

NASA NTRS1983

The role of magnetic fields in stellar chromospheres and transition regions

Consideration is given to the different roles that magnetic fields play in the control of the structure and energy balance in the chromospheres and transition regions of late-type stars, in view of IUE and Einstein satellite observations. The rotational modulation of structures ('plages') that are bright in UV emission lines and overlie dark star spots suggests that magnetic flux tubes are the dominant structural elements in late-type stellar atmospheres, as well. It is proposed that the existence of a boundary between solar-type stars and those with little or no plasma, as well as the different types of G-K giants and supergiants, may be understood in terms of the fractional surface coverage by closed magnetic structures. Models computed for active and quiet regions of the sun are compared with those for active and quiet stars.

Linsky, J. L.↗

NASA NTRS1986

Modeling for CO poisoning of a fuel cell anode

Poisoning losses in a half-cell in the 110-190 C temperature range have been measured in 100 wt pct H3PO4 for various mixtures of H2, CO, and CO2 gases in order to investigate the polarization loss due to poisoning by CO of a porous fuel cell Pt anode. At a fixed current density, the poisoning loss was found to vary linearly with ln of the CO/H2 concentration ratio, although deviations from linearity were noted at lower temperatures and higher current densities for high CO/H2 concentration ratios. The surface coverages of CO were also found to vary linearly with ln of the CO/H2 concentration ratio. A general adsorption relationship is derived. Standard free energies for CO adsorption were found to vary from -14.5 to -12.1 kcal/mol in the 130-190 C temperature range. The standard entropy for CO adsorption was found to be -39 cal/mol per deg K.

Dhar, H. P.↗

NASA NTRS1990

Energetics of molecular-beam epitaxy models

The removal energies of constituent atoms from various unreconstructed semiconductor surfaces are calculated using a Green function method. An efficient difference-equation approach within the second-neighbor tight-binding model is employed. For a compound AB, binding energies for the A and B atoms on the (111), (-1 -1 -1), (100), and (110) surfaces are calculated. Analyses are made of the energy to remove an atom from the nearly full surface and from the nearly empty surface. Results are presented for Si, GaAs, CdTe, and HgTe; and the surface sublimation energies are found to depend on surface coverage and do not display a simple linear relationship to the number of bonds broken, as is often assumed in modeling growth by MBE.

Krishnamurthy, Srinivasan↗

NASA NTRS1991

HCl dissolved in solid mixtures of nitric acid and ice - Implications for the polar stratosphere

The solubility of HCl in polar stratospheric cloud (PSC) particles plays an important role in the heterogeneous chemistry of the lower polar stratosphere. New laboratory studies are reported showing a strong dependence of the HCl solubility on the HNO3 content in ice particles. At 200 K and a partial HCl pressure of 10 exp -6 torr, the HCl content in NAT is 0.35 mol pct, decreasing about a factor of 3 for every ten-fold decrease in the substrate's HNO3 content. At an HCl pressure of 10 exp -7 torr, the content is about 40 percent of that at 10 exp -6 torr. HCL dissolved in pure water ice at these partial pressures is less than 0.002 mol pct. The surface coverage of HCl on small ice samples was estimated to be about 0.1 monolayer at 10 exp -6 torr exposure.

Marti, James↗

NASA NTRS1992

Interleaving Magellan altimetry data acquisition between mapping cycles 1 and 2

The Magellan spacecraft has been systematically mapping the surface of Venus since September 15, 1990, using side-looking synthetic aperture radar imaging and nadir-pointed altimetry. Venus rotates slowly under the nearly polar mapping orbit, completing a full revolution in 243 days, one 'mapping cycle'. The altimeter collects a 10 km swath of altitude measurements each orbit. The groundtrack advances 21 km each orbit due to the rotation of Venus, leaving an 11 km gap of unmeasured terrain. To obtain global surface coverage by the altimeter, these gaps are eliminated by interleaving the swaths collected during the second mapping cycle with those from the first mapping cycle. Interleaving was put into effect by a propulsive maneuver, executed at the end of the first mapping cycle, on May 17, 1991. The orbit node was changed by +0.106 degrees, so that the cycle 2 groundtracks would bisect adjacent cycle 1 groundtracks. This paper describes the maneuver design and execution results, including the problem and solution of the groundtrack prediction to the end of the first mapping cycle.

Engelhardt, D. B.↗

NASA NTRS1992

Potentiostatic and ac impedance studies of the hydrogen electrodes used in Ni/H2 batteries

In a study of electrode activity for hydrogen evolution and hydrogen ionization, knowledge of the detailed kinetics and of the surface coverage by adsorbed hydrogen is essential. In the Ni/H2 battery, the hydrogen electrode is subjected to high hydrogen pressure; elucidation of the variation of kinetic parameters with hydrogen pressure is therefore of interest. Potentiostatic and ac impedance spectroscopic techniques were used in the present study. The equivalent circuit of the reaction, the kinetic parameters, and their pressure dependence have been determined.

Le Helloco, Jean-Guy↗

NASA NTRS2001

Lunar Crustal Magnetism: Correlations with Geology

With Lunar Prospector reflectometry data we now have sufficient surface coverage to allow detailed comparisons between crustal magnetism and geology. We find substantial evidence that lunar magnetism is dominated by the effects of impact processes. Additional information is contained in the original extended abstract.

Halekas, J. S.↗

NASA NTRS2002

Sensor Web Architectural Concepts and Implementation Challenges - An Heuristic Approach

There is a significant interest in the Earth Science remote sensing community to increase the number of observations. The obvious reasons for such a push is to improve the temporal and surface coverage of measurements. However, there is little analysis available in terms of benefits, costs and optimized set of sensors needed to make these necessary observations. In reality, this is a complex problem that should be carefully studied and balanced over many boundaries. For example, the question of technology maturity versus users desire to obtain additional measurements is non congruent. This is further complicated by the limitations of the laws of physics and the economic conditions. With the advent of advance technology, it is anticipated that the cost of the spacecraft technology will become more affordable. However, the specialized detector subsystems, and the precision flying techniques may still require substantial innovation, development time and cost. Additionally, the space deployment scheme should also be given a careful attention because of a high expense. Nonetheless, it is important to carefully examine the science priorities and steer the development efforts that can commensurate with the tangible requirements. This paper outlines a possible set of architectural concepts, operational scenarios and potential benefits of one scheme versus another. It further makes some suggestions where one can draw some boundary conditions to incrementally solve this predicament.

Habib, Shahid↗