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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

A simulation of saltation dynamics with application to terrestrial and Martian model surfaces.

The feasibility of predicting the saltation threshold from a dynamic model of the saltation process is demonstrated. The model is based on mechanical equations that describe the trajectories of particles (sand grains) near the ground-atmosphere interface. The equations of particle motion are formulated in terms of forces and moments. The forces employed are based on theoretical and experimental results obtained for continuum flow. Surface structuring analytics and simulated fluid turbulence further modify the particle behavior. The model is used to predict the threshold velocities on Mars.

Andres, R. M.↗
NASA NTRS1973

Ten-micron eclipse observations of Io, Europa, and Ganymede.

Eclipse observations of Jupiter's satellites Io, Europa, and Ganymede have been obtained in an 8 to 14-micron band pass during 1971. The simplest thermal model able to explain the data for each satellite is a two-layer surface structure with an upper layer, only a few millimeters thick, having low thermal conductivity consistent with fine rock powder or frost, and a subsurface having high thermal conductivity consistent with solid rock or dense ice. The upper layer on Io appears to be different from that on Europa and Ganymede, but the two-layer model fits all three satellites.

Hansen, O. L.↗
NASA NTRS1973

The nature of circular maria based on gravity studies.

Current thinking on the evolution of major lunar morphological features, i.e., large lunar circular basins, and on the nature and origin of surface structures observed in the fill deposits is summarized. The great lunar circular basins must result from high-velocity impact of large bodies with the moon. A hydrostatic mechanism is outlined, and a working hypothesis is presented for the evolution of lunar circular basins subsequent to their origin by impact. In the main appeal is made to Doppler gravity data to support the hypothesis, although photographic and altimetric information is also used. It is considered that all large ringed circular basins follow a common evolutionary path of superisostatic volcanic flooding followed by partial and variable isostatic adjustment. The difference between basins is the amount of flooding, which in turn may be related to the center of figure-center of mass offset of the moon.

Phillips, R. J.↗
NASA NTRS1973

The Apollo 17 Lunar Sounder.

The Apollo Lunar Sounder Experiment (ALSE) was a three-frequency wide-band coherent radar system operated from lunar orbit during the Apollo 17 mission. The scientific objectives of the experiment include the mapping of subsurface structure, surface profiling, surface imaging, and galactic noise measurement. Examples of subsurface reflections are discussed, giving attention to VHF sounding, HF2 sounding, and HF1 sounding. Examples of imagery and profiles are also considered, taking into account various craters and profile high points.

Phillips, R. J.↗
NASA NTRS1974

Six-color photometry of Iapetus, Titan, Rhea, Dione and Tethys

The extensive photometric observations of Titan, Iapetus, Rhea, Dione and Tethys have made it possible to separate the solar phase and orbital phase contributions to the observed light variations of these satellites. For Titan, the wavelength dependence of its solar phase coefficient has been obtained. This dependence should prove useful in constructing future model atmospheres. The other four satellites show a surprising array of different photometric behaviors. Despite these differences, all four satellites have similar spectral reflectivities. Clearly Iapetus, Rhea, Dione and Tethys are complex objects, varying substantially from one another in surface structure and/or composition.

Noland, M.↗
NASA NTRS1973

The Apollo 17 Lunar Sounder

The Apollo Lunar Sounder Experiment, a coherent radar operated from lunar orbit during the Apollo 17 mission, has scientific objectives of mapping lunar subsurface structure, surface profiling, surface imaging, and galactic noise measurement. Representative results from each of the four disciplines are presented. Subsurface reflections have been interpreted in both optically and digitally processed data. Images and profiles yield detailed selenomorphological information. The preliminary galactic noise results are consistent with earlier measurements by other workers.

Phillips, R. J.↗
NASA NTRS1974

Analysis for Mar Vel Black and acetylene soot low reflectivity surfaces for star tracker sunshade applications

Mar Vel Black is a revolutionary new extremely low reflectivity anodized coating developed by Martin Marietta of Denver. It is of great interest in optics in general, and in star trackers specifically because it can reduce extraneous light reflections. A sample of Mar Vel Black was evaluated. Mar Vel Black looks much like a super black surface with many small peaks and very steep sides so that any light incident upon the surface will tend to reflect many times before exiting that surface. Even a high reflectivity surface would thus appear to have a very low reflectivity under such conditions. Conversely, acetylene soot does not have the magnified surface appearance of a super black surface. Its performance is, however, predictable from the surface structure, considering the known configuration of virtually pure carbon.

Yung, E.↗
NASA NTRS1975

IPL processing of the Mariner 10 images of Mercury

This paper describes the digital processing performed on the images of Mercury returned to earth from Mariner 10. Each image contains considerably more information than can be displayed in a single picture. Several specialized processing techniques and procedures are utilized to display the particular information desired for specific scientific analyses: radiometric decalibration for photometric investigations, high-pass filtering to characterize morphology, modulation transfer function restoration to provide the highest possible resolution, scene-dependent filtering of the terminator images to provide maximum feature discriminability in the regions of low illumination, and rectification to cartographic projections to provide known geometric relationships between features. A principal task was the construction of full disk mosaics as an aid to the understanding of surface structure on a global scale.

Soha, J. M.↗
NASA NTRS1976

Acceleration of fatigue tests for built-up titanium components

A study was made of the feasibility of a room-temperature scheme of accelerating fatigue tests for Mach 3 advanced supersonic transport aircraft. The test scheme used equivalent room-temperature cycles calculated for supersonic flight conditions. Verification tests were conducted using specimens representing titanium wing lower surface structure. Test-acceleration parameters were developed for the test with an auxiliary test set. Five specimens were tested with a flight-by-flight load and temperature spectrum to simulate typical Mach 3 operation. Two additional sets of five specimens were tested at room temperature to evaluate the test-acceleration scheme. The fatigue behavior of the specimens generally correlated well with the proposed correction method.

Watanabe, R. T.↗
NASA NTRS1975

Skylab analysis of San Francisco Bay

The distribution and volume of sediment present in suspension during the Skylab 4 overpass for San Pablo Bay and the Carquinez Strait is studied along with the movement and eventual distribution of both natural and dredged sediment in San Francisco Bay. The most useful Skylab sensor film is found to be the S-190B color photography. Changes in temperature, dissolved oxygen, pH, salinity, and pollutants information simultaneously collected are correlated with the spectral differences observed in the various Skylab data. The techniques outlined should be applicable for coastal and estuarine process studies in other areas. A suspensate concentration of about 2 mg/liter is quite sufficient to tag a surface current system, and the surface structure of currents with over 250 mg/liter can be imaged by using progressively longer wavelength filters.

Steller, D. D.↗
NASA NTRS1977

Models of radar imaging of the ocean surface waves

A number of models which would explain ocean wave imagery taken with a synthetic aperture imaging radar are analyzed analytically and numerically. Actual radar imagery is used to support some conclusions. The models considered correspond to three sources of radar backscatter cross section modulation: tilt modulation, roughness variation, and the wave orbital velocity. The effect of the temporal changes of the surface structure, parametric interactions, and the resulting distortions are discussed.

Elachi, C.↗
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

Analytical model of the combustion of multicomponent solid propellants

Multiple flame models derived for simple composite propellants are extended to describe the combustion of propellants containing multimodal particle sizes, mixed oxidizers and monopropellant binders. Models combining the component contributions to propellant surface structure, flame structure and energy distribution are based in part upon experimental observations and in part upon hypotheses constrained to provide reasonable agreement with measured burning rate characteristics. The methods employed consist of superposition, interaction and iteration. The computerized model is applied to explain the effects of multiple ingredients and to discuss burning rate tailoring problems of current interest.

Cohen, N. S.↗
NASA NTRS1977

Nitramine smokeless propellant research

A transient ballistics and combustion model is derived to represent the closed vessel experiment that is widely used to characterize propellants. A computer program is developed to solve the time-dependent equations, and is applied to explain aspects of closed vessel behavior. In the case of nitramine propellants the cratering of the burning surface associated with combustion above break-point pressures augments the effective burning rate as deduced from the closed vessel experiment. Low pressure combustion is significantly affected by the ignition process and, in the case of nitramine propellants, by the developing and changing surface structure. Thus, burning rates deduced from the closed vessel experiment may or may not agree with those measured in the equilibrium strand burner. Series of T burner experiments are performed to compare the combustion instability characteristics of nitramine (HMX) containing propellants and ammonium perchlorate (AP)propellants. Although ash produced by more fuel rich propellants could have provided mechanical suppression, results from clean-burning propellants permit the conclusion that HMX reduces the acoustic driving.

Cohen, N. S.↗
NASA NTRS1978

Optical observations of the sun from a solar probe

The spatial resolution of solar surface structure to ultimate limits with simple instrumentation. The logic is simple: a 10 cm aperture telescope at 4 solar radii resolves the equivalent of a five meter telescope in earth orbit. Given the ease of producing a diffraction limited 10 cm telescope and the difficulty of fabricating a diffraction limited 5 meter telescope, the performance of the small telescope could well be better. The telescope described complements planned solar orbiting telescopes in earth orbit and would need only a few arcs seconds of pointing.

Zirin, H.↗
NASA NTRS1978

Ion beam sputtering of fluoropolymers

Ion beam sputter processing rates as well as pertinent characteristics of etched targets and films are described. An argon ion beam source was used to sputter etch and deposit the fluoropolymers PTFE, FEP, and CTFE. Ion beam energy, current density, and target temperature were varied to examine effects on etch and deposition rates. The ion etched fluoropolymers yield cone or spire-like surface structures which vary depending upon the type of polymer, ion beam power density, etch time, and target temperature. Sputter target and film characteristics documented by spectral transmittance measurements, X-ray diffraction, ESCA, and SEM photomicrographs are included.

Sovey, J. S.↗
NASA NTRS1978

Mutual phenomena of Jupiter's five inner satellites in 1979

In this paper, we first predict eclipses and occultations of the Galilean satellites in 1979 and find that, although circumstances are generally poor, about 75 events are observable. We have then made a special point of including 40 eclipses of J5 (Amalthea) by the Galilean satellites in the hope that both visual and far-infrared light curves can be obtained - the former giving accurate astrometric information for J5, and the latter possible bearing on its surface structure or composition.

Aksnes, K.↗
NASA NTRS1978

Analytical model of high pressure burning rates in a transient environment

A transient ballistics and combustion model is derived to represent the closed vessel experiment that is widely used to characterize the high pressure burning rates of solid propellants. The model is applied to explain why burning rates deduced from the closed vessel are in basic agreement with those measured from an equilibrium strand burner in the case of homogeneous propellants, but differ significantly in the case of nitramine composite propellants. Thermal profile time lag effects become small at high pressure because the burning rates become high. However, the development of the burning surface structure of those nitramine propellants which exhibit shifts in pressure exponent causes the mass burning rate to lag and then exceed the equilibrium value. It is necessary to consider this mechanism in applications dealing with high pressures and pressurization rates.

Cohen, N. S.↗