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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Origin and evolution of the lunar surface - The major questions remaining

The major factors in the evolution of the lunar surface have not been determined yet. Huge lava flows and lunar differentiation, though commonly assumed, is in discord with much of the evidence. The alternative is for most of the surface to represent the last stages of accretion of the moon only, with the chemical differentiation having taken place previously in the source material. Radar, seismic, surface exposure, and mascon evidence can then be accounted for. A large-scale surface transport mechanism of soil must then have been present.

Gold, T.↗
NASA NTRS1981

Mercury - Magnetospheric processes and the atmospheric supply and loss rates

It is pointed out that the solar wind is an important contributor to the H and He components of the atmosphere of Mercury. For this reason, and because significant differences exist between the magnetospheres of Mercury and the earth, an investigation was conducted of the magnetospheric processes at Mercury to determine how these processes affect the precipitation of solar wind plasma onto the planetary surface. Attention is given to a review of estimates of the Hermaean magnetic moment, the direct impact of the solar wind on the planetary surface, precipitation along closed dayside magnetic field lines, precipitation along open dayside magnetic field lines, particles precipitating on closed field lines from the plasma sheet, radiogenic and other atmospheric sources, atmospheric loss rates, surface interaction mechanisms, and subsurface residence times and chemical reactions.

Goldstein, B. E.↗
NASA NTRS1982

Effects of environment on microhardness of magnesium oxide

Micro-Vickers hardness measurements of magnesium oxide single crystals were conducted in various environments. These environments included air, nitrogen gas, water, mineral oil with or without various additives, and aqueous solutions with various pH values. Indentations were made on the (100) plane with the diagonals of the indentation in the (100) direction. The results indicate that a sulfur containing additve in mineral oil increased hardness, a chlorine containing additive in mineral oil decreased hardness, and aqueous solutions of hydrogen chloride decreased hardness. Other environments were found to have little effect on hardness. Mechanically polished surfaces showed larger indentation creep than did as-cleaved surfaces.

Ishigaki, H.↗
NASA NTRS1982

Spaceborne synthetic-aperture imaging radars - Applications, techniques, and technology

In June 1978, the Seasat satellite was placed into orbit around the earth with a synthetic-aperture imaging radar (SAR) as one of the payload sensors. The Seasat SAR provided, for the first time, synoptic radar images of the earth's surface with a resolution of 25 m. In November 1981, the second imaging radar was successfully operated from space on the Shuttle. The Shuttle Imaging Radar-A acquired images over a variety of regions around the world with an imaging geometry different from the one used by the Seasat SAR. The spaceborne SAR principle is discussed, taking into account ambiguities, orbital and environmental factors, range curvature and range walk, surface interaction mechanisms, thermal and speckle noise, key tradeoff parameters, and nonconventional SAR systems. Attention is also given to spaceborne SAR sensors, the digital processing of spaceborne SAR data, the optical processing of spaceborne SAR data, postimage formation processing, data interpretation techniques and applications, and the next decade.

Elachi, C.↗
NASA NTRS1983

Oxygen atom reaction with Shuttle materials at orbital altitudes - Data and experiment status

Significant surface characteristics changes have been noticed on materials that were exposed in the payload bay of the Space Shuttle Orbiter on the first four flights. The most notable change was mass loss of Kapton film used as a component of thermal blankets. This film exhibited as much as 35 percent mass loss on STS-3 and loss of material was noticed on all flights. Other changes consist of rapid aging of paints and oxidation of Torlon surfaces. A mechanism has been proposed for the effects described, which involves the interaction of these organic materials with atomic oxygen available at low earth orbital altitudes. Evidence derived from measurements made on Shuttle materials that supports this mechanism will be presented. Experiments planned for near-term Shuttle flights are being developed to obtain quantitative data on reaction rates.

Leger, L.↗
NASA NTRS1982

Effect of Y2O3 and Al2O3 on the oxidation resistance of Si3N4

Oxidation of cold-pressed and sintered Si3N4 containing 15 wt% Y2O3 and 2, 4, 6, and 8% Al2O3 is observed at temperatures as low as 1000 C with IR reflection spectroscopy. Concentrations of Al2O3 in excess of 4% greatly retard the rate of oxidation and alter the mechanism of surface attack by promoting formation of a glassy layer on the surface containing mixed oxynitride bonds. The glassy layer retards heterogeneous attack and reduces the effect of an oxidation transition temperature between 1000 and 1100 C for these materials.

Hench, L. L.↗
NASA NTRS1984

Analysis of instability-related growth of a through-width delamination

The effect of various parameters on instability related delamination growth was studied. The configuration studied consisted of a thick composite laminate with a single through width delamination located near one surface. Both mechanical and thermal loads were considered. It is assumed that GI and GII govern delamination growth. An approximate superposition stress analysis was developed which gives closed form expressions for GI and GII. It is found that both GI and GII are very sensitive to delamination length and location through the thickness and that the magnitude of GI is also sensitive to initial imperfection. Critical loads for delamination growth are calculated based on three growth criteria. Large differences in the predictions highlight the need for a verified mixed mode delamination growth criterion.

Whitcomb, J. D.↗
NASA NTRS1985

Formation of high molecular weight products from benzene during boundary lubrication

High molecular weight products were detected on the wear track of an iron disk at the end of a sliding friction and wear test using benzene as a lubricant. Size exclusion chromagography in conjunction with UV analysis gave evidence that the high molecular weight products are polyphenyl ether type substances. Organic electrochemistry was used to elucidate the possible surface reaction mechanisms.

Morales, W.↗
NASA NTRS1986

Parametric analytical study of instability-related delamination growth

The effect of various parameters on instability-related delamination growth was studied analytially. The configuration studied consisted of a thick composite laminate with a single through-width delamination located near one surface. Both mechanical and thermal loads were considered. All conclusions were based on the assumption that GI and GII govern delamination growth. An approximate superposition stress analysis was developed which gives closed form expressions for GI and GII. The simplicity of the analysis permitted examination of numerous configurations. Both GI and GII were found to be very sensitive to delamination length and location through the thickness. The magnitude of GI was also very sensitive to initial imperfections, which might be the results of an inclusion of finite thickness in the delamination. Critical loads for delamination growth were calculated based on three growth criteria. Large differences in the predictions highlight the need for a verified mixed-mode delamination growth criterion.

Whitcomb, J. D.↗
NASA NTRS1987

Voyager 2 photopolarimeter observations of the Uranian satellites

The surfaces of the principal Uranian satellites are characterized on the basis of UV and IR geometric albedos, phase curves, and phase coefficients obtained in full-disk photopolarimetric observations during the Voyager 2 encounter with Uranus in January 1986. The data are presented in tables and graphs and found to be consistent with a heavily cratered terrain and loosely packed regolith. The Bond albedos are calculated as 0.22 + or - 0.1 for Ariel, 0.07 + or - 0.05 for Umbriel, 0.16 + or - 0.12 for Titania, and 0.19 + or - 0.22 for Oberon. The characteristics of the Uranian satellites indicate compositions (and probably formation conditions and surface-modification mechanisms) distinct from those of the Saturnian and Jovian satellites.

Nelson, Robert M.↗
NASA NTRS1988

Sampling the ancient volatile-rich areas of Mars

Viking images clearly show areas with a high density of fluidized craters that also display a significant number of wrinkle ridges. Fluidized crater ejecta morphology may indicate that the target material was rich in volatiles at the time of the impact. Therefore, these areas are of the utmost importance in deciphering both the Martian tectonic evolution and the amount of subsurface water, at times when more favorable conditions for life to evolve did exist on Mars. Although a large number of extensional features are associated with Tharsis and Elysium geologic activity, the planet-wide distribution of ridges suggests that Mars' tectonic history is far more complex than the Tharsis-dominated scenario indicates. Like on the Moon and Mercury, ridges on Mars were formed under compressive stresses, probably as a result of thrust-fault mechanism, although surface expressions and direct causes vary. Martian ridges are most easily seen on smooth plains of volcanic origin, but the majority of the 16,000 mapped and classified compressive features are located in the old terrains, far beyond Tharsis influence.

Chicarro, A. F.↗
NASA NTRS1988

The keyhole region in VPPA welds

The morphology and properties of the Variable Polarity Plasma Arc (VPPA) weld composite zone are intimately related to the physical processes associated with the keyhole. The effects of microsegregation and transient weld stress on macrosegregation in the weld tool are examined. In addition the electrical character of straight and reverse polarity portions of the arc cycle were characterized. The results of the former study indicate that alloy 2219 is weldable because large liquid volumes are available during latter stages of weld solidification. Strains in the pool region, acting in conjunction with weld microsegregation can produce macrosegregation great enough to produce radiographic contrast effects in welds. Mechanisms of surface copper enrichment were identified. The latter study has demonstrated that increased heat is delivered to workpieces if the reverse polarity proportion of the weld cycle is increased. Current in the straight polarity portion of the welding cycle increased as the reverse cycle proportion increased. Voltage during reverse polarity segments is large.

Walsh, Daniel W.↗
NASA NTRS1991

Survey of results from the Boeing modules on the M0003 experiment on LDEF

The Boeing modules on the M0003 experiment included fiber optics, ceramic materials, a variety of electronic piece parts, composites and thermal control paints, fasteners, thin film lubricants, anodized surfaces, and adhesives. These materials were flown on the leading and trailing edge exteriors, and on the interior portion of LDEF M0003 providing exposure under three distinct environments. The condition of each of these material types is described. Results of optical, surface, and mechanical properties are presented.

Pippin, H. Gary↗
NASA NTRS1991

Variable features in the Valles Marineris region of Mars

Transient phenomena on Mars have long been recognized in Mariner and Viking images as well as in decades of Earth based telescopic observations. These events are of interest because of the information they present on currently active meteorological and geological processes. Changes in surface albedo patterns and atmospheric conditions can also affect the analysis and interpretation of data based on spectral or morphological properties of geologic units on the surface. The mechanism responsible for albedo pattern change is currently under investigation. Generation and subsequent transportation and deposition of dark sands has been interpreted in the Valles. However, the removal of a bright dust layer is more consistent with the rapid time period of the change (about two months) and with preliminary multispectral mapping results which suggest that the dark streak south of Eos and Coprates Chasmata is spectrally distinguishable from the dark saltating materials found elsewhere in the canyon system. If a layer of bright dust was removed to affect the albedo change, questions concerning how such micron-sized particles are mobilized by the winds during a normally quiescent season (Southern Hemisphere Autumn) should be addressed.

Geissler, Paul E.↗
NASA NTRS1991

High resolution lunar radar studies: Preliminary results

High resolution radar data for the lunar surface were acquired over 14 sites in June and November 1990 using the new 10 MHz data taking system at the Arecibo Observatory. The raw data collected for each site covers an area approximately 100 by 400 km and will be processed using delay-Doppler techniques into images of backscatter cross section with three fo four independent looks. All observations transmitted a circularly polarized signal and both senses of circular polarization were received containing the polarized and depolarized component of the backscatter signal. The relative power in these two polarizations provides useful information on properties of the surface, in particular surface roughness. The effort to date focused on the initial data analysis with new software written to perform a full synthetic aperture focusing on the raw radar data. This analysis will involve the use of complementary high resolution optical and topographic data sets to aid interpretation of surface scattering mechanisms.

Stacy, Nicholas J. S.↗
NASA NTRS1993

Current status of liquid sheet radiator research

Initial research on the external flow, low mass liquid sheet radiator (LSR), has been concentrated on understanding its fluid mechanics. The surface tension forces acting at the edges of the sheet produce a triangular planform for the radiating surface of width, W, and length, L. It has been experimentally verified that (exp L)/W agrees with the theoretical result, L/W = (We/8)exp 1/2, where We is the Weber number. Instability can cause holes to form in regions of large curvature such as where the edge cylinders join the sheet of thickness, tau. The W/tau limit that will cause hole formation with subsequent destruction of the sheet has yet to be reached experimentally. Although experimental measurements of sheet emissivity have not yet been performed because of limited program scope, calculations of the emissivity and sheet lifetime is determined by evaporation losses were made for two silicon based oils; Dow Corning 705 and Me(sub 2). Emissivities greater than 0.75 are calculated for tau greater than or equal to 200 microns for both oils. Lifetimes for Me(sub 2) are much longer than lifetimes for 705. Therefore, Me(sub 2) is the more attractive working fluid for higher temperatures (T greater than or equal to 400 K).

Chubb, Donald L.↗