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At least 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Evidence for convection in planetary interiors from first-order topography.

Center of mass/center of figure offsets are known for the earth, moon, Mars and Venus. Such an offset requires a density distribution asymmetric about the center of mass. Observational evidence indicates that the terrestrial, lunar and Martian offsets result from crusts of variable thickness rather than lateral density inhomogeneities and that the thickness variations are more likely caused by internal convection than impact.

Lingenfelter, R. E.↗
NASA NTRS1973

Surface features on Mars: Ground-based albedo and radar compared with Mariner 9 topography

Earth-based albedo maps of Mars were compared with Mariner 9 television data and ground-based radar profiles to investigate the nature of the bright and dark albedo features. Little correlation was found except at the boundaries of classical albedo features, where some topographic control is indicated. Wind-blown dust models for seasonal and secular albedo variations are supported, but it is not clear whether the fines are derived from bright or dark parent rock. Mars, like the Earth and Moon, has probably generated two distinct types of crustal material.

Frey, H.↗
NASA NTRS1974

Effect of surface topography on structural growth of thick sputtered films

Primarily thick sputtered S-Monel, silver, and 304 stainless steel coatings were deposited on mica, glass, and metal substrates with various surface finishes to investigate the structural growth of the coating by scanning electron microscopy. Compositional changes within the coating were analyzed by X-ray dispersion microscopy. Defects in the surface finish act as preferential nucleation sites and form isolated and complex nodules and various surface overgrowths in the coating. These nodules do not disappear after full annealing. Further, they have undesirable effects on mechanial properties; cracks are initiated at the nodules when the coating is stressed by mechanical forces. These effects are illustrated by micrographs. Nodular growth within a coating can be minimized or eliminated by reducing the surface roughness.

Spalvins, T.↗
NASA NTRS1972

Gravimetric geodesy and sea surface topography studies by means of satellite-to-satellite tracking and satellite altimetry

A satellite-to-satellite tracking experiment is planned between ATS-F and GEOS-C with a range accuracy of 2-meters and a range rate accuracy of 0.035 centimeters per second for a 10-second integration time. This experiment is planned for 1974. It is anticipated that it will improve the spatial resolution of the satellite geoid by half an order of magnitude to about 6 degrees. Longer integration times should also permit a modest increase in the acceleration resolution. Satellite altimeter data will also be obtained by means of GEOS-C. An overall accuracy of 5-meters in altitude is the goal. The altimeter, per se, is expected to have an instrumental precision of about 2 meters, and an additional capability to observe with a precision of about 0.2 meters for limited periods.

Siry, J. W.↗
NASA NTRS1974

Topography of aortic heart valves

The cooperative effort towards the development of a tri-leaflet prosthetic heart valve is described. The photogrammetric studies were conducted on silicone rubber molds. Information on data acquisition and data reduction phases is given, and certain accuracy aspects of the project are explained. The various outputs which are discussed include digital models, profiles, and contour maps.

Karara, H. M.↗
NASA NTRS1973

Lunar topography from Apollo 15 and 16 laser altimetry

In the orbital plane of Apollo 15 the mean lunar radius is 1737.3 km, the mean altitude of terrae above maria is about 3 km, and the center-of-figure is displaced from the center-of-mass by about 2 km away from longitude 25 E. The Apollo 16 laser altimeter obtained a total of about 7.5 revolutions of partially overlapping data. The principal difference in results from Apollo 16 is the absence of any great far-side basin similar to the 1400-km wide feature found by Apollo 15, 1200 km to the south. This absence of a far-side depression in the Apollo 16 orbital plane largely accounts for a greater mean radius: 1738.1 km; a greater mean altitude of terrae above maria: about 4 km; and a greater offset of centers: about 3 km, also away from 25 E. In the Apollo 16, as well as Apollo 15, data the far-side terrae are much 'rougher' than the near-side terrae. Mare surfaces are generally smooth to within plus or minus 150 m, and have slopes of 1:500 to 1:2000 persisting over distances as great as 500 km.

Kaula, W. M.↗