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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Astrometric observations and the motion of comet Halley

Beginning with studies related to the 1835 appearance of comet Halley, it became apparent that comets may undergo substantial nongravitational perturbations due to the rocket-like effect of an outgassing cometary nucleus. Marsden (1968, 1969) modeled these nongravitational effects with a semiempirical term in the cometary equations of motion. The most successful orbital solution was consistent with an outgassing water ice nucleus in direct rotation. For the conduction and coordination of accurate astrometric observations of comet Halley, an Astrometry Network is being established within the International Halley Watch program. Attention is given to the support of the Halley flight projects provided by the Astrometry Network, and the support of ground based observers by this network.

Yeomans, D. K.↗
NASA NTRS1984

Composition, Structure and Evolution of Uranian and Neptunian Satellites

Large uncertainties in the current estimated densities of all of these satellites prevent detailed modeling or predictions. Nevertheless, current evidence suggests that at least Titania and Oberon might have anomalously high densities of 2-39 cm(-3), possibly requiring almost ice-free hydrated silicates or formation in a CO-rich environment, implying presence of CO-clathrate and a small ice/rock ratio. Trition and the four largest satellites of Uranus are massive enough to have undergone significant accretional heating and early differentiation; NH3-H2O volcanism; partial outgassing of CO, N2, Ch4; formation of dark surficial deposits of carbon-rich material obtained by UV irradiation of outgassed material; and, at least in the cases of Ariel and Triton, a possibility of weak ongoing icy volcanic activity. Triton may be the largest captured body in the solar system, with an unusual history and composition, including the possibility of substantial liquid or solid nitrogen obtained from either primordial NH3 photolysis or clathrate decomposition.

Stevenson, D. J.↗
NASA NTRS1985

The degassing history of the Earth: Noble gas studies of Archaean cherts and zero age glassy submarine basalts

Recent noble gas studies suggests the Earth's atmosphere outgassed from the Earth's upper mantle synchronous with sea floor spreading, ocean ridge hydrothermal activity and the formation of continents by partial melting in subduction zones. The evidence for formation of the atmosphere by outgassing of the mantle is the presence of radionuclides H3.-4, Ar-040 and 136 Xe-136 in the atmosphere that were produced from K-40, U and Th in the mantle. How these radionuclides were formed is reviewed.

Hart, R.↗
NASA NTRS1985

Water loss from Venus: Implications for the Earth's early atmosphere

The atmosphere of Venus outgassed rapidly as a result of planetary heating during accretion, resulting in massive water loss. The processes affecting atmospheric chemistry following accretion have consisted largely of hydrogen escape and internal re-equilibrium. The initial bulk composition of Venus and Earth are assumed to have been roughly similar. Chemical speciation on Venus was controlled by the temperature and oxygen buffering capacity of the surface magma. It is also assumed that the surfaces of planetary bodies of the inner solar system were partly or wholly molten during accretion with a temperature estimated at 1273 to 1573 K. To investigate the range of reasonable initial atmospheric compositions on Venus, limits have to be set for the proportion of total hydrogen and the buffered fugacity of oxygen. Using the C/H ratio of 0.033 set for Earth, virtually all of the water generated during outgassing must later have been lost in order to bring the current CO2/H2O ratio for Venus up to its observed value of 10 sup 4 to 10 sup 5. The proportion of H2O decreases in model atmospheres with successfully higher C/H values, ultimately approaching the depleted values currently observed on Venus. Increasing C/H also results in a rapid increase in CO/H2O and provides an efficient mechanism for water loss by the reaction CO+H2O = CO2 + H2. This reaction, plus water loss mechanisms involving crustal iron, could have removed a very large volume of water from the Venusian atmosphere, even at a low C/H value.

Richardson, S. M.↗
NASA NTRS1984

Interplanetary field enhancements in the solar wind - Evidence for cometesimals at 0.72 and 1.0 AU?

A new class of interplanetary magnetic disturbance has been identified which consists of a nearly symmetric rise and fall of the magnetic field surrounding a cusp-shaped maximum. These disturbances have been hypothesized to be caused by the mass-loading of the solar wind by small outgassing bodies. The clustering of these events in space suggests that not all the events are independent. Clustering is greatest at 0.72 AU because of one very strong family of events associated with the orbit of the asteroid 2201 0ljato. The events are larger at 0.72 AU than at 1 AU. The timing of the disturbances at both 1 AU and 0.72 AU relative to 0ljato suggests the presence of outgassing debris both in front of and behind the asteroid.

Arghavani, M. R.↗
NASA NTRS1985

The evolution of CO2 on Mars

At the surface, the atmosphere of Mars contains approximately 95.3 percent CO2 by volume. At the Viking Lander 1 (VL1) site, the total surface pressure varied with the season between about 6.89 and 8.94 mbar. Questions related to the observed CO2 pressure on Mars are explored. Several published estimates of the total amount of CO2 outgassed over the history of Mars, varying between 140 and 3000 mbar, are shown in a table. It is pointed out that the study of likely reservoirs for outgassed CO2 has focused mainly on the polar caps and regolith. Constraints on the formation of transitory pockets of moist soil are discussed, taking into account heat requirements, supply of water, and constraints related to pressure. Attention is also given to chemical considerations, implications for the current status of CO2 reservoirs, and scenarios for the evolution of CO2 pressure.

Kahn, R.↗
NASA NTRS1988

Samples for estimating primary volatiles in Martian magmas and ancient atmospheric pressures on Mars

Inclusions of glass are likely to be present in phenocrysts in volcanic rocks from Mars, because these occur in volcanic rocks from both Earth and Moon. The usefulness of the inclusions depends upon their size and composition. The compositions of tiny inclusions may be modified by diffusion during growth of the enclosing crystal, the modifications increasing with melt viscosity (silica). Slow cooling results in crystallization and possible redistribution of volatiles, the effects increasing with decreasing silica. Primary volatile concentrations are best sought in inclusions larger than about 50 micrometer diameter in olivine or chromite crystals from quickly cooled basaltic scoria. Such crystals may be present in sands, but it would be preferable to extract them from individual rocks which could be dated and compositionally characterized. This would allow eventual understanding of the role of time and place in outgassing and volcanism on Mars. Analyses of volatiles in inclusions of more siliceous glass in non-basaltic rocks will reveal whether deep outgassing occurs and whether surface volatiles are recycled. Most volcanic crystals contain inclusions, but large inclusions can be uncommon. In the case of terrestrial basalts sample masses of several hundred grams are generally sufficient.

Anderson, A. T., Jr.↗
NASA NTRS1988

Controls of CO2 sources and sinks in the earth scale surface ocean - Temperature and nutrients

Several regions in the ocean in which disequilibrium persists on an annual avarage between CO2 in the surface water and the overlying atmosphere were examined using various models in which CO2 does cycle in a steady state at which sources (ocean outgassing) and sinks (ingassing) are in balance. The relative values of the surface temperature and surface nutrients, the two major contributors to the CO2 source and/or sink properties, are determined. Results from models with two ocean surfaces indicate that the sink in the north Atlantic and the sources in the equatorial Atlantic and Pacific are all dominated by the global temperature patterns. Results from ocean models with three surface zones show that, in the equatorial Pacific, the temperature control is responsible for over 50 percent (and, possibly, for almost 70 percent) of the CO2 outgassing, with the balance coming from the earth scale surface nutrient structure.

Volk, Tyler↗
NASA NTRS1989

Measurement of damping of graphite epoxy composite materials and structural joints

The damping capacity of graphite epoxy materials and structural joints was evaluated. The damping ratio of different composite specimens and bonded joints were systematically evaluated under normal atmospheric conditions and in a vacuum environment. Free and forced vibration test methods were employed for measuring the damping ratios. The effect of edge support conditions on the damping value of a composite tube specimen was studied by using a series of experiments performed on the specimen with different edge supports. It was found that simulating a free-free boundary conditions by having no constraints at the ends gives the lowest value of the material damping of the composite. The accuracy of the estimation of the damping ratio value was improved by using a curve-fitting technique on the response data obtained through measurement. The effect of outgassing (moisture desorption) on the damping capacity was determined by measuring the damping ratio of the tube specimen in a vacuum environment before and after outgassing had occurred. The effects of high and low temperatures on the damping was also investigated by using a series of experiments on tube and beam specimens. An analytical model to study the vibrations of a bonded lap joint system was formulated. Numerical results were generated for different overlap ratios of the system. These were compared with experimental results. In order to determine the influence of bonded joints on the material damping capacity, experiments were conducted on bonded lap-jointed and double-butt-jointed specimens. These experimental results were compared with simple beam specimens with no joints.

Crocker, Malcolm J.↗
NASA NTRS1991

Reactive Fluorescent Dyes For Urethane Coatings

Molecules of fluorescent dyes chemically bound in urethane conformal-coating materials to enable nondestructive detection of flaws in coats through inspection under ultraviolet light, according to proposal. Dye-bonding technique prevents outgassing of dyes, making coating materials suitable for use where flaw-free coats must be assured in instrumentation or other applications in which contamination by outgassing must be minimized.

Willis, Paul B.↗
NASA NTRS1990

The growth of zinc selenide single crystals by physical vapor transport in microgravity

Growth and characterization studies will be performed on zinc selenide single crystals. The high temperature outgassing behavior of the silica ampoule material will be studied in order to develop a cleaning and bake-out procedure that will minimize the amount of impurities introduced into the vapor from the ampoule materials and in particular during the seal-off procedure. The outgassing behavior of the ZnSe starting material will be studied during high vacuum refinement at elevated temperatures in order to develop a temperature pressure program that will optimize the removal of impurities while minimizing a shift in stoichiometry due to preferred evaporation of the higher fugacity component. The mass spectrometer system was completed, and after calibration, will be used to perform the above tasks. The system and its operation is described in detail.

Anderson, Elmer E.↗
NASA NTRS1990

VLA searches for formaldehyde and cyanoacetylene emission from comet P/Brorsen-Metcalf (1989o)

In Sep. 1989, Very Large Array (VLA) searches were conducted for both formaldehyde (H2CO) and cyanoacetylene (HC3N) emission from Comet P/Brorsen-Metcalf (1989o). In early July, this comet was outgassing strongly at a brighter than average preperihelion rate, and the hope was that it would continue to do so through perihelion. By observing the 1 sub 11 to 1 sub 10 transition of H2CO at 4,829.659 MHz (6 cm lambda) during the phase of maximum outgassing, it was expected that spectra would be collected with a high signal to noise ratio which would show the temporal behavior of formaldehyde relative to other molecules. During this same observation period, a search was also made for the J-1-0, F-2-1 rotational transition of cyanoacetylene at 9098.3321 MHz (3.3 cm lambda).

Snyder, Lewis E.↗
NASA NTRS1991

Organic contamination of LDEF

A brown stain of varying thickness was present on most of the exterior surface of the retrieved Long Duration Exposure Facility (LDEF). Tape lifts of Earth-end LDEF surfaces taken showed that the surface particle cleanliness immediately after retrieval was very good, but faint footprints of the tape strips on the tested surfaces indicated a very faint film was removed by the tape. Solvent wipes of these surfaces showed that the stain was not amenable to standard organic solvent removal. Infrared spectra of optical windows from tray E5 show that the organic film is hydrocarbon in composition, but is not similar to the oil that seeped from tray C12. Very dark and heavy deposits of the stain is present at openings and vents to the interior of LDEF. Heavy brown and blue-green deposits are present in the interior of LDEF where sunlight penetrated through cracks and vent openings. The exterior of LDEF had significant areas painted with a white polyurethane paint for thermal control, and almost all of the interior was painted with a black polyurethane paint. Brown staining is consistent with outgassing of hydrocarbons from these paints by rapid solar UV induced polymerization of the outgassed hydrocarbons when they hit sunlight exposed areas.

Harvey, Gale A.↗
NASA NTRS1991

Detection of CN emission from (2060) Chiron

The detection of CN emission the spectrum of (2060) Chiron not only underscores its cometary nature, but represents, at a heliocentric distance in excess of 11 AU, the most distantly detected instance of a cometary gas species. These observations are noted to be consistent with a driving of Chiron's outgassing by isolated outbursts of CO2 from a small fraction of Chiron's surface. If dusty particles or icy grains are dragged out by the gas with unit dust-to-gas mass ratio, outbursts need occur only once every several months. Such small-surface outgassings appear to characterize comets which have made many passages close to the sun.

Bus, Schelte J.↗
NASA NTRS1991

MOLFLUX analysis of the SSF electrical power system contamination

The external induced contamination of Space Station Freedom's electrical power system surfaces is assessed using a molecular flow evaluation code, MOLFLUX. Outgassing rates are compared to available experimental data, and deposition to the midregion of both the solar array and the photovoltaic power module thermal control system radiator is calculated using a constant sticking coefficient. An estimate of annual deposition to the solar array due to outgassing is found to be 10 percent of the Space Station Freedom program requirement for maximum allowable deposition, while annual deposition to the radiator is approximately equal to the requirement.

Cognion, Rita L.↗
NASA NTRS1990

Analysis and interpretation of Wide Field Planetary Camera outgas data collected in the temperature range from -20 C to -100 C

The data from the Wide Field Planetary Camera (WFPC) are analyzed to determine the absolute source-emission parameters and contaminant reemission parameters of outgassing mass accumulation. The data correspond to the mass accumulated on a -100 C quartz crystal microbalance and then desorbed at -50 C as a function of time. The parameters investigated include contaminant mass, first-order rate constants, and characteristic energies. The data are modeled in terms of a minimum number of species characterized by source-rate and reemission-rate parameters. The modeling technique is found to produce adequate fits, and the contaminants that accumulate at -100 C and desorb at -50 C do not accumulate at -50 C. The data analysis is found to be an adequate technique for assessing outgassing parameters for the prediction of WFPC internal contamination.

Barengoltz, Jack B.↗
NASA NTRS1991

Minor planet 1566 Icarus: Asteroid or comet?

By employing a cometary nongravitational force model, based on the outgassing of a water ice nucleus, the orbital fits to the optical and radar astrometric data are improved for both Apollo and Icarus. A reliable value for the magnitude of these nongravitational effects can be determined for Icarus, but not Apollo. Because Icarus is less than a kilometer in extent, the small amount of outgassing required to explain its anomalous orbital behavior would probably not be sufficient to create an easily visible coma. While these results do not prove that 1566 Icarus is an active comet masquerading as an asteroid, this object certainly deserves future scrutiny to determine its true identity. A near-Earth asteroid showing cometary activity must represent only the tip of a much larger cometary iceburg. For such an object whose aphelion is well inside Jupiter's orbit, the time scale for losing its volatiles is much shorter than the time scale for evolving out of the inner solar system. Thus, for each active member of the near-Earth asteroid population, there must be many more that are temporarily or permanently inactive.

Yeomans, Donald K.↗
NASA NTRS1992

Atomic oxygen effects on thermal control and mirror coatings: Evaluation of experiment A0034

Evaluation of the degradation attributed to contamination of the collector mirrors in Experiment A0034, which were exposed to an earth orbital environment while on the leading and trailing edges of the LDEF, has provided some evidence for outgassing of coatings stimulated by atomic oxygen. Effects of the natural space environment on the coatings and mirrors, including the effects of incident and re-directed atomic oxygen flux, were investigated. The effects of exposure on the coatings and mirrors were evaluated by optical, surface profiling, chemical, and scanning electron microscopy (SEM) measurements. Preliminary results of these analyses are discussed for application to both the issues of mirror and coating stability and the specific issue of atomic oxygen stimulated outgassing.

Linton, Roger C.↗