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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 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Distribution and state of H2O in the high-latitude shallow subsurface of Mars

The state and distribution of H2O molecules at high latitudes are evaluated numerically with emphasis on the effects of seasonal temperatures on the kinetics of H2O transport. The investigation is carried out with a thermal model for the regolith regions from the surface through the ice interface and an atmospheric model for the H2O vapor density at the surface as a function of latitude. Few differences are found in the state and distribution of H2O whether the regolith is composed of Montmorillonite or basalt. During an obliquity cycle, the average exchanged H2O mass is determined to be in the range 1-20 gr/sq cm over the planetary surface, with a total maximum exchanged volume of 1500 cu km of H2O. The exchanged mass would arise mainly from ground ice in the case of a basalt regolith and from adsorbed H2O with Montmorillonite. Finally, seasonal ice stabilization is expected to occur at latitudes above 40 deg when obliquities exceed 25 deg.

Zent, A. P.↗
NASA NTRS1978

Time delay occultation data of the Helios spacecraft for probing the electron density distribution in the solar corona

S-band time delay measurements were collected from the spacecraft Helios A and B during three solar occultations in 1975/76 within heliocentric distances of about 3 and 215 earth radius in terms of range, Doppler frequency shift, and electron content. Characteristic features of measurement and data processing are described. Typical data sets are discussed to probe the electron density distribution near the sun (west and east limb as well) including the outer and extended corona. Steady-state and dynamical aspects of the solar corona are presented and compared with earth-bound-K-coronagraph measurements. Using a weighted least squares estimation, parameters of an average coronal electron density profile are derived in a preliminary analysis to yield electron densities at r = 3, 65, 215 earth radius. Transient phenomena are discussed and a velocity of propagation v is nearly equal to 900 km/s is determined for plasma ejecta from a solar flare observed during an extraordinary set of Helios B electron content measurements.

Edenhofer, P.↗
NASA NTRS1972

The thermodynamic properties of nitrogen from 65 to 2000 K with pressures to 10,000 atmospheres

An equation of state is presented for liquid and gaseous nitrogen for temperatures from 65 degrees K to 2000 degrees K and pressures to 10,000 atmospheres. All the pressure-density-temperature data available from published literature have been corrected and applied to bring experimental temperatures into accord with the International Practical Temperature Scale of 1968. The coefficients of the equation of state were determined by a weighted least squares fit to selected published pressure-density-temperature data. The methods of weighting the various data for simultaneous fitting are presented and discussed.

Jacobsen, R. T.↗
NASA NTRS2000

Insights Developed Into the Damage Mechanism of Teflon FEP Thermal Control Material on the Hubble Space Telescope

Metalized Teflon FEP (DuPont; fluorinated ethylene propylene) thermal control material on the Hubble Space Telescope (HST) has been found to degrade in the space environment. Teflon FEP thermal control blankets retrieved during the first servicing mission were found to be embrittled on solar-facing surfaces and to contain microscopic cracks (the FEP surface is exposed to the space environment). During the second servicing mission, astronauts noticed that the FEP outer layer of the multilayer insulation blanketing covering the telescope was cracked in many locations. Large cracks were observed on the light shield, forward shell, and equipment bays. A tightly curled piece of cracked FEP from the light shield was retrieved during the second mission. This piece was severely embrittled, as witnessed by ground testing. A Failure Review Board was organized by NASA Goddard Space Flight Center to determine the mechanism causing the multilayer insulation degradation. This board included members of the Electro-Physics Branch of the NASA Glenn Research Center at Lewis Field. Density measurements of the retrieved materials obtained under the review board's investigations indicated that FEP from the first servicing mission was essentially unchanged from pristine FEP but that the second servicing mission FEP had increased in density in comparison to pristine FEP (ref. 1). The results were consistent with crystallinity measurements taken using x-ray diffraction and with results from solid-state nuclear magnetic resonance tests (see the table and ref. 1). Because the second servicing mission FEP was embrittled and its density and crystallinity had increased in comparison to pristine FEP, board researchers expected that the first servicing mission FEP, which was also embrittled, would also have increased in crystallinity and density, but it did not. Because the retrieved second servicing mission material curled while in space, it experienced a higher temperature extreme during thermal cycling (estimated at 200 C) than the first servicing mission material (estimated at 50 C). Therefore, Glenn initiated and conducted an investigation of the effects of heating pristine FEP and FEP that had been exposed on the Hubble Space Telescope. Samples of pristine and first and second servicing mission FEP were heated to 200 C and evaluated for changes in density and morphology. We hoped that the results would help explain why FEP degrades in the Hubble Space Telescope space environment.

deGroh, Kim K.↗
NASA NTRS1990

A model for the spectral dependence of optically induced absorption in amorphous silicon

A model based on transitions from localized band tail states to states above the mobility edge is used to explain the broad band induced absorptions observed in recent pump-probe experiments. The model gives the observed decrease of absorption with frequency at subband gap photo energies and high carrier densities (of about 10 to the 20th/cu cm). At lower carrier densities, the absorption has a maximun which is sensitive to the spatial extent of the band tail states.

Lawandy, N. M.↗
NASA NTRS1986

Latitudinal plasma distribution in the dusk plasmaspheric bulge - Refilling phase and quasi-equilibrium state

Very low-energy trapped ions, mostly protons, have been observed in a region of moderate density characteristic of the plasmapause boundary and of the plasmaspheric bulge. The present paper is concerned with an examination of the latitudinal structure of the bulge under quasi-steady conditions and the conditions of the recovery phase. Details regarding the data base are considered along with observations of the morphology and dynamics of the bulge, the latitudinal density distribution in the expanded bulge, the convection scenario during the replenishment phase, and latitudinal effects on plasma characteristics during plasmasphere refilling. The data utilized have been mainly provided by the DE 1 and GEOS 2 spacecraft traveling in two perpendicular planes. It is found that the bulge is a dynamic region, where no reasonable interpretation of the observed density distribution can be achieved without taking into account the mechanism of magnetospheric convection.

Decreau, P. M. E.↗
NASA NTRS1992

Effect of fiber orientation on the fracture toughness of brittle matrix composites

The effective fracture toughness of brittle matrix materials can be increased through the addition of short, poorly bonded fibers which bridge the growing crack. The orientation distribution of the fibers is likely to be biased, and not in an ideal random or aligned state. A micromechanical model is formulated for the postcracking behavior using the force-displacement relation for an arbitrary fiber bridging a crack, the fiber orientation density function, and the fiber location density function. This model is then used to determine an effective traction law for the bridging fibers, as well as the steady state bridging toughness increment. In most cases, the results may be placed in the form of a product of the aligned fiber results times a modifying integrated orientation factor. The frictional shear stress on fiber pull-out is allowed to vary during pull-out, modeling the effects of matrix breakdown, fiber surface smoothing or wear debris accumulation. Results are presented for a variety of representative planar and three-dimensional fiber orientation states.

Jain, L. K.↗
NASA NTRS2000

Reconnection in Planetary Magnetospheres

Current sheets in planetary magnetospheres that lie between regions of "oppositely-directed" magnetic field are either magnetopause-like, separating plasmas with different properties, or tail-like, separating plasmas of rather similar properties. The magnetopause current sheets generally have a nearly limitless supply of magnetized plasma that can reconnect, possibly setting up steady-state reconnection. In contrast, the plasma on either side of a tail current sheet is stratified so that, as reconnection occurs, the plasma properties, in particular the Alfven velocity, change. If the density drops and the magnetic field increases markedly perpendicular to the sheet, explosive reconnection can occur. Even though steady state reconnection can take place at magnetopause current sheets, the process often appears to be periodic as if a certain low average rate was demanded by the conditions but only a rapid rate was available. Reconnection of sheared fields has been postulated to create magnetic ropes in the solar corona, at the Earth's magnetopause, and in the magnetotail. However, this is not the only way to produce magnetic ropes as the Venus ionosphere shows. The geometry of the reconnecting regions and the plasma conditions both can affect the rate of reconnection. Sorting out the various controlling factors can be assisted through the examination of reconnection in planetary settings. In particular we observe similar small-scale tearing in the magnetopause current layers of the Earth, Saturn. Uranus and Neptune and the magnetodisk current sheet at Jupiter. These sites may be seeds for rapid reconnection if the reconnection site reaches a high Alfven velocity region. In the Jupiter magnetosphere this appears to be achieved with resultant substorm activity. Similar seeds may be present in the Earth's magnetotail with the first one to reach explosive growth dominating the dynamics of the tail.

Russell, C. T.↗
NASA NTRS2024

Measuring the Density, Viscosity, and Surface Tension of Molten Titanates Using Electrostatic Levitation in Microgravity

Rare earth and barium titanates are useful as ferroelectric, dielectric, and optical materials. Measurements of their thermophysical properties in the liquid state can help guide melt processing technologies for their manufacture and advance understanding of fragile liquids' behavior and glass formation. Here, we report the density, thermal expansion, viscosity, and surface tension of molten BaTiNsub>2 O 5 , BaTi 4 O 9 , and 83TiO 2 -17RE 2 O 3 (RE = La or Nd). Measurements were made using electrostatic levitation and droplet oscillation techniques in microgravity, which provide access to quiescent liquid droplets and deep supercooling of 510–815 K below the equilibrium melting points. Densities were measured over 900–2400 K. Viscosities were similar for all four compositions, increasing from ∼10 mPa s near 2100 K to ∼30 mPa s near 1750 K. Surface tensions were 450–490 dyn cm −1 for the rare earth titanates and 383–395 dyn cm−1 for the barium titanates; surface tensions of all compositions had small or negligible temperature dependence over 1700–2200 K. For solids recovered after melt quenching, x-ray microtomography revealed the fracture mechanics in crystalline products and minimal internal porosity in glass products, likely arising from entrapped gas bubbles. Internal microstructures were generally similar for products processed either in microgravity or in a terrestrial aerodynamic levitator.

Stephen K Wilke↗
NASA NTRS1971

A study of nitride devices for computer memory applications

Metal-nitride-oxide-silicon /MNOS/ capacitors act like metal-nitride-silicon /MNS/ capacitors with extra interface where sheet of charge can be stored in slow states. Flatband voltage shifts over a wide range by adjusting store charge density.

Raburn, W. D.↗
NASA NTRS1974

High performance dc-dc conversion with voltage multipliers

The voltage multipliers using capacitors and diodes first developed by Cockcroft and Walton in 1932 were reexamined in terms of state of the art fast switching transistors and diodes, and high energy density capacitors. Because of component improvements, the voltage multiplier, used without a transformer, now appears superior in weight to systems now in use for dc-dc conversion. An experimental 100-watt 1000-volt dc-dc converter operating at 100 kHz was built, with a component weight of about 1 kg/kW. Calculated and measured values of output voltage and efficiency agreed within experimental error.

Harrigill, W. T.↗
NASA NTRS1974

Ovonic switching in tin selenide thin films

Amorphous tin selenide thin films which possess Ovonic switching properties were fabricated using vacuum deposition techniques. Results obtained indicate that memory type Ovonic switching does occur in these films the energy density required for switching from a high impedance to a low impedance state is dependent on the spacing between the electrodes of the device. The switching is also function of the magnitude of the applied voltage pulse. A completely automated computer controlled testing procedure was developed which allows precise control over the shape of the applied voltage switching pulse. A survey of previous experimental and theoretical work in the area of Ovonic switching is also presented.

Baxter, C. R.↗
NASA NTRS1975

Ovonic type switching in tin selenide thin films

Amorphous tin selenide thin films which possess Ovonic type switching properties are fabricated using vacuum deposition techniques. The devices are fabricated in a planar configuration and consist of amorphous tin selenide deposited over silver contacts. Results obtained indicate that Ovonic type memory switching does occur in these films with the energy density required for switching from a high impedance to a low impedance state being dependent on the spacing between the electrodes of the device. There is also a strong implication that the switching is a function of the magnitude of the applied voltage pulse.

Baxter, C. R.↗
NASA NTRS1979

Synchronous orbit power technology needs

An attempt is made to define the needs for future geosynchronous spacecraft power subsystem components, including power generation, energy storage, and power processing. Three projected models (a mission model, an orbit transfer vehicle model, and a mass model) for power subsystem components are used to define power requirements and mass limitations for future spacecraft. Based upon these models, the power subsystems for a 10-kW, 10-year-life, dedicated spacecraft and for a 20-kW, 20-year-life multimission platform are analyzed to establish power density requirements for orbit transfer vehicles. Comparison of these requirements to state-of-the-art (Intelsat 5) design values shows that major improvements, by a factor of 2 or more, are needed to accomplish the near term missions.

Slifer, L. W., Jr.↗
NASA NTRS1979

Coordinated rocket and satellite measurements of an auroral event. II - The rocket observations and analysis

A rocket-borne payload launched into an aurora and a simultaneous overpass of the Atmosphere Explorer C satellite yielded measurements of auroral optical emission rates, thermal ion and electron densities, and low-energy electron fluxes. Model calculations of the thermospheric manifestation of the aurora were performed through use of rocket-determined auroral ionization rates and satellite-determined neutral gas densities. Measured oxygen densities provided a means of assessing the quenching rate of an excited state of N2. Energy transfer from this excited state appears to be the major source of 5577-A emission. Optical emission at 6300 A cannot be explained either by electron impact on atomic oxygen or by dissociative recombination of O2(+).

Sharp, W. E.↗
NASA NTRS1980

Measuring radiation effects on MOS capacitors

Electron injection technique serves as powerful probe of trapped hole distribution after irradiation because it was determined that electrons only annihilate trapped holes. Other effects, such as other electron traps and interface state generation, are negligible in injection range used. Trap cross sections and densities indicate at least three trap species; interfacial species, dominant bulk species determined to tail off from silicon interface, and lower density and cross section species that may be distributed throughout bulk of oxide.

Bakowski, M.↗
NASA NTRS1983

Stimulated emission and the flat Balmer decrements of cataclysmic variable stars

Balmer emission lines from cataclysmic variables often have nearly equal intensities rather than the rapid decrement predicted by simple nebular theory. Traditionally, this has been interpreted in terms of local thermodynamic equilibrium emission from a dense gas with small volume located just above the accretion disk. It is shown that the intense radiation field within a close binary system can affect excited state populations and optical emission in ways which allow a relatively low density gas to closely mimic the high density situation. In at least one case, the old nova V603 Aql, the emitting gas has a low density and nearly fills the orbital plane of the system. If this is characteristic of other systems, then the determination of orbital parameters and masses of cataclysmic variables from emission line radial velocities, as well as the prediction of soft X-ray emission from accreting binaries, will be affected.

Elitzur, M.↗
NASA NTRS1987

Noise and compressibility in lattice-gas fluids

Computations are reported in which the hexagonal lattice gas is used to simulate two-dimensional Navier-Stokes shear flows. Limitations associated with noise in the initial loading and compressible effects associated with a velocity-dependent equation of state arise and interact with each other. A relatively narrow window in density and flow speed exhibits physical behavior.

Dahlburg, Jill P.↗