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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 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Numerical solution of the Navier-Stokes equations with topography

A finite difference scheme for solving the equations of fluid motion in a generalized coordinate system has been constructed. The scheme conserves mass and all the first integral moments of the motion. The scheme also advectively 'almost conserves' second moments, in that the magnitude of implicit numerical smoothing is typically about an order smaller than explicit viscosity and diffusion. Calculations with the model support the theoretical conjecture that the difference scheme is stable whenever the analogous Cartesian scheme is stable. The scheme has been used to calculate dry atmospheric convection due to differential heating between top and bottom of mountainous terrain. The general small-scale characteristics of mountain up-slope winds have been simulated. In addition, the results have demonstrated the crucial role played by the eddy diffusivities and the environmental stability, in determining both the quantitative and the qualitative features of the circulation.

Gal-Chen, T.↗
NASA NTRS1975

Martian topography derived from occultation, radar, spectral, and optical measurements

A new global topographic map of the planet Mars, derived primarily from Mariner 9 data, is presented. Spacecraft radio signal occultation times, remote sensing of infrared and ultraviolet spectra, and earth-based radar measurements are included in the data base. Large-scale topographic relief is seen with definite fluid flow patterns established over much of the surface consistent with earlier analyses. An optical flattening of 0.0059 is obtained with a center-of-mass to center-of-figure offset of approximately 2 km to the south and 1 km toward the Tharsis ridge. Mathematical models approximating the topographic figure and 6.1-mb isobaric surface for Mars are included in this presentation.

Christensen, E. J.↗
NASA NTRS1975

Topography of the polar layered deposits of Mars

Synthesis of polar topographic data derived from the Mariner 9 radio occultation, ultraviolet spectrometer, and television imaging experiments provides new information on the behavior of polar volatiles and the topographic configuration of the Martian polar layered deposits. Gentle slopes in the vicinity of the south pole may serve to shift the point of minimum annual solar insolation from the pole to a site within the perimeter of the offset residual frost cap. Localized defrosting which gives rise to the dark-banded appearance of both residual caps correlates with a series of outward-facing slopes descending from central topographic highs. Stability of the volatile involved apparently is largely insolation controlled. The south polar residual cap lies entirely higher (at lower pressure) than the northern cap, implying that the south residual cap is an unlikely site for any permanent surface deposit of solid carbon dioxide.

Dzurisin, D.↗
NASA NTRS1975

Radar measurements of Martian topography and surface properties - The 1971 and 1973 oppositions

The Goldstone radar system was used at a wavelength of 12.6 cm to probe the Martian surface during the 1973 opposition. Measurements of range and reflected power were made at least weekly between July 12 and November 24. Surface cells isolated by the radar system were 8 km E-W by 110 km N-S. Altitudes were calculated from signal time delays measured relative to a triaxial ellipsoid and were combined with altitudes measured during the 1971 opposition. Contours of constant altitude were calculated at 200 m intervals between latitudes -14 and -22 deg. These contours are presented in conjunction with Mars charts derived from Mariner 9 television pictures. Reflected power was measured at angles of incidence between -5 and +5 deg. These measurements were combined with those obtained during the 1971 opposition.

Downs, G. S.↗
NASA NTRS1977

X-ray topography as a process control tool in semiconductor and microcircuit manufacture

A bent wafer camera, designed to identify crystal lattice defects in semiconductor materials, was investigated. The camera makes use of conventional X-ray topographs and an innovative slightly bent wafer which allows rays from the point source to strike all portions of the wafer simultaneously. In addition to being utilized in solving production process control problems, this camera design substantially reduces the cost per topograph.

Parker, D. L.↗
NASA NTRS1977

Topography of sinuous rilles in the Harbinger Mountains region of the moon

Five sinuous rilles in mare basalts in the Harbinger Mountains region of the moon are described. Rille length ranges from 12 to 79 km, width from 0.8 to 4.8 km, and depth from 100 to 300 m. The rilles appear to become shallower to the north, while the southern ends are characterized by circular-to-elongate depressions that occur on a 30-km-in-diameter dome of probable volcanic origin. Longitudinal profiles show that the rille floors have a northward slope of less than one deg, consistent with the general slope of the surrounding mare surface. Structural studies indicate that slope, rather than the regional structural pattern, is the dominant factor controlling rill direction. Topographic data support the theory that the rilles were formed as lave channels or tubes.

Strain, P. L.↗
NASA NTRS1977

Antarctic ice topography and 150 mb circulation from the Nimbus-6 TWERL Experiment

Many TWERLE balloons floating at an altitude of about 12.5 km, traversed the Antarctic during its 1975/6 summer. The balloons' positions were accurately determined by the Nimbus-6 satellite, which also received their sensors' data: radio altimeter, pressure and temperature. Subtracting the altimeter readings from the calculated balloon altitude above sea-level (a.s.l.) provides the Antarctic surface elevation at the balloon subtrack. The balloon altitude a.s.l. is calculated from daily synoptic maps covering latitudes south of 45 deg S. These maps are prepared using the regular radiosonde network supplemented by four times as many TWERLE balloons.

Levanon, N.↗
NASA NTRS1978

Determination of some dominant parameters of the global dynamic sea surface topography from GEOS-3 altimetry

The 1977 altimetry data bank is analyzed for the geometrical shape of the sea surface expressed as surface spherical harmonics after referral to the higher reference model defined by GEM 9. The resulting determination is expressed as quasi-stationary dynamic SST. Solutions are obtained from different sets of long arcs in the GEOS-3 altimeter data bank as well as from sub-sets related to the September 1975 and March 1976 equinoxes assembled with a view to minimizing seasonal effects. The results are compared with equivalent parameters obtained from the hydrostatic analysis of sporadic temperature, pressure and salinity measurements of the oceans and the known major steady state current systems with comparable wavelengths. The most clearly defined parameter (the zonal harmonic of degree 2) is obtained with an uncertainty of + or - 6 cm. The preferred numerical value is smaller than the oceanographic value due to the effect of the correction for the permanent earth tide. Similar precision is achieved for the zonal harmonic of degree 3. The precision obtained for the fourth degree zonal harmonic reflects more closely the accuracy expected from the level of noise in the orbital solutions.

Mather, R. S.↗
NASA NTRS1978

Ice sheet topography by satellite altimetry

The measured time between the transmission and rzturn of 13.9 GHz radar pulses from the GEOS 3 satellite (at a mean altitude of 844.5 km and an inclination of 114 deg 52 min) is used to determine the thickness of the Greenland ice cap, with an accuracy in surface elevation on the order of 2 m. Attention is given to changes in ice thickness as an indicator of climatic change in general, and change in mean sea level in particular. Each elevation data point obtained by the satellite represents an average along 0.67 km of ground track, and three-dimensional maps are presented to illustrate the data.

Brooks, R. L.↗
NASA NTRS1978

Volcanoes on the inner planets - Some preliminary comparisons of gross topography

The paper extends previous numerical work on analogs of planetary landform (Pike, 1974, 1978) by concentrating on volcanic edifices rather than impact craters. Two kinds of extraterrestrial volcanic constructs - domes on the lunar maria and calderas on Mars - are compared with terrestrial volcanoes. According to available data, neither type of landform unequivocally resembles a specific class of terrestrial volcano. The quantitative models of volcanoes presented necessarily are statistical because the shapes of volcanic landforms vary over a wide range of values.

Pike, R. J.↗
NASA NTRS1979

Global tectonic studies: Hotspots and anomalous topography

Volcanic activity on Earth and its secular variations are compared with that on other terrestrial planets. Activity at divergent, transform, and convergent plate margins is described with particular emphasis on hot spots and flood basalts. The timing and causing of uplifting above 500 meters, which in not associated with either plate boundaries or the normal nonplate margin edges of continents is considered with particular focus on the Guyana Highlands in southern Venezuela and western British Guiana, and the Brazilian Highlands in the central, eastern, and southern parts of the country. The mode and mechanism of plateau uplifting and the re-elevation of old mountain belts and subsidence of intra-continental basins are also discussed.

Burke, K.↗
NASA NTRS1979

Topography and tectonics of mid-oceanic ridge axes

Numerical fluid dynamic models of mid-oceanic ridge axes were constructed using distributions of material properties constrained by seismic studies and thermal calculations. The calculations indicate that spreading is passive except for forces caused by density differences due to thermal expansion and partial melt. Except for geometric differences due to temperature distribution, one set of mechanical properties can adequately explain central rifts of slow ridges and central peaks of fast ridges. Viscous head loss in the upwelling material dominates at low spreading rates where material ascends through a narrow conduit. Thermal expansion and partial melting dominate at high spreading rates where a wide low viscosity crustal magma chamber is present. The preferred rheology is 10 to the 20th poise for the upwelling lithosphere; less than 5 x 10 to the 17th for the crustal magma chamber and axial intrusion zone at fast ridges, and a yield stress of 200 bars for the lithosphere. The calculation correctly predicts the existence of central peaks at 'hot-spot' ridges, where seismic evidence indicates a large magma chamber.

Sleep, N. H.↗
NASA NTRS1979

Smythii basin topography and comparisons with Orientale

The Smythii basin has the most extensive topographic coverage of any lunar multi-ringed basin. Topographic data are used to study the morphology and morphometry of Smythii and to make comparisons with similar basins. The depth of the basin is shown to be over 8 km, which is comparable to that of Orientale. The inner ring reaches heights of 3.4 km, while the intermediate ring exhibits little relief. Lowest points in the basin are related to mare ridges. Basin volume is estimated to be 21 million cubic kilometers. Evidence suggests that significant differences in substrate characteristics may have existed for the Smythii and Orientale impacts.

Strain, P. L.↗
NASA NTRS1978

Bent crystal X-ray topography

A television X-ray topographic camera system was constructed. The system differs from the previous system in that it incorporates the X-ray TV imaging system and has a semi-automatic wafer loading system. Also the X-ray diffraction is in a vertical plane. This feature makes wafer loading easier and makes the system compatible with any commercial X-ray generating system. Topographs and results obtained from a study of the diffraction contrast variation with impurity concentration for both boron implanted and boron diffused silicon are included.

Parker, D. L.↗