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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 1,063 records · Page 59
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NASA NTRS1984

Turbulent heating in solar cosmic-ray theory

The heating of minor ions in solar flares by wave-wave-particle interaction with Langmuir waves, or ion acoustic waves, can be described by a diffusion equation in velocity-space for the particle distribution function. The dependence of the heating on the ion charge and mass, and on the composition of the plasma, is examined in detail. It is found that the heat mechanisms proposed by Ibragimov and Kocharov cannot account for the enhanced abundances of heavy elements in the solar cosmic rays.

Weatherall, J.↗
NASA NTRS1980

Solar modulation of galactic cosmic rays

The current theory for the solar modulation of galactic cosmic rays is reviewed briefly. The four basic mechanisms which are important for modulation-diffusion, effects associated with the large-scale magnetic field, convection, and energy change - are discussed in simple terms. The equation which describes cosmic-ray behavior in the heliosphere is presented and some sample solutions are considered. It is pointed out that, although the basic mechanisms which describe the cosmic-ray behavior are understood, the actual cause of the variation in the cosmic-ray flux over the solar cycle, or over longer intervals, is beyond current comprehension.

Fisk, L. A.↗
NASA NTRS1972

Structure and variations of the heterosphere

Atmospheric composition is kept almost homogeneous to a height of approximately 90 km (the homosphere) by mixing; above 100 km (the heterosphere), diffusive separation of the atmospheric constituents occurs. The heterosphere is dominated by two energy sources: solar extreme ultraviolet radiation and the solar wind. Many large variations are observed in this region and they can all be related, directly or indirectly, to variations in the intrinsic intensity of these two sources and to variations in the location of the sources relative to the observer. Atmospheric models can be successfully constructed in which the temperature and density variations are empirically related to solar and geomagnetic parameters. Some of the more recent findings concerning the structure and variations in the heterosphere are presented.

Jacchia, L. G.↗
NASA NTRS1977

Solar wind plasma injection at the dayside magnetospheric cusp

Two mechanisms have been proposed for solar wind particle injection at the dayside magnetospheric cusps: magnetic merging and cross-field diffusion. These two mechanisms are experimentally distinguishable in that they produce different latitudinal distributions of particles penetrating to the low-altitude cusp. An examination of proton and electron measurements obtained by the AE-C satellite in the low-altitude dayside cusp reveals evidence of both types of injection processes. A majority of the injection events, especially the more intense fluxes, are best explained by a merging injection model in which cusp particles are confined to the poleward side of the last closed field line and have a characteristic energy that decreases with increasing latitudinal distance from the last closed field line. Less frequent and less intense injection events are better explained in terms of a diffusive injection of cusp particles onto closed dayside field lines with a characteristic energy that increases with increasing latitudinal distance from the last closed field line. Although diffusion appears to be quantitatively less important than merging in terms of the instantaneous particle injection rate, cross-field diffusion nevertheless appears to proceed at an unexpectedly fast rate, possibly exceeding the Bohm diffusion limit.

Reiff, P. H.↗
NASA NTRS1984

Formation and dynamics of large-scale magnetic structures in the ionosphere of Venus

The formation and dynamics of large-scale magnetic structures in the ionosphere of Venus are examined. It is shown that such structures must be the result of steady state convection of interplanetary field lines into the ionosphere by the small amount of solar wind plasma (less than or approximately equal to 1-5 percent) absorbed by the planetary atmosphere below the ionopause, rather than isolated remnants of large fields persisting for long periods without connection to the solar wind induced current and convection pattern. In particular, it is demonstrated that the magnetic diffusion of such structures would result in their dissipation with time scales of 1-10 min, if they were not steady state structures in convective and diffusive equilibriuim. It is shown that the equations governing the diffusion of these magnetic structures are similar to those governing diffusion of a gas out of an enclosed chamber with a porous wall, and a simple analog is illustrated. The application of these results to magnetic fields of astrophysical plasmas is discussed.

Cloutier, P. A.↗
NASA NTRS1987

Gamma-ray constraints on Na-22 yields in nova explosions

The longitudinal distribution of diffuse 1.275 MeV emission produced by the decay of interstellar Na-22 generated by a limited class of energetic novae-accreting ONeMg white dwarfs is modeled. The probability distributions for the locations of disk novae are derived as functions of Galactocentric cylindrical coordinates. The occurrence rate for novae of all classes in the Galactic disk is about 30/yr. An occurrence rate of about 16/yr is found for spheroid novae of all classes. By comparing these simulation results with HEAO 3 upper limits on diffuse 1.275 MeV emission, upper limits of (3-5.6) x 10 to the -7th solar mass are determined for the mean Na-22 yield for energetic novae generated by accreting ONeMg white dwarfs. These Na-22 limits constrain future models of explosive nucleosynthesis in energetic nova explosions.

Higdon, J. C.↗
NASA NTRS1989

Hydrogen line and continuum emission in young stellar objects. II - Theoretical results and observational constraints

Theoretical results for H I emission from YSOs are compared with available observations. IR line and radio continuum properties have been gathered for 29 objects that include a number of T Tau stars, several emission-line stars with IR excesses, and many heavily obscured luminous YSOs. The present excitation model can account for the observed Brackett line and radio continuum fluxes of YSOs with luminosities of 20-100,000 solar luminosities. It is argued that the observed Br-alpha line and 6-cm free-free continuum emissions are best explained in terms of a core-halo structure. The small core (ranging from r less than about 30 AU for a 10,000-solar luminosity YSO to r less than about 0.2 AU for a 10-solar luminosity YSO) is responsible for generating the strong IR line fluxes, while the surrounding diffuse halo dominates the 6-cm emission.

Alonso-Costa, Jose L.↗
NASA NTRS1989

A new calculation of the cosmic-ray antiproton spectrum in the Galaxy and heliospheric modulation effects on this spectrum using a drift plus wavy current sheet model

The expected interstellar antiproton spectrum arising from cosmic-ray interactions in the Galaxy is recalculated, and the modulation of both antiprotons and protons is calculated using a two-dimensional modulation model incorporating gradient and curvature drifts and a wavy current sheet as well as the usual diffusion, convection, and energy-loss effects. Significant differences in the antiproton/proton ratio for different solar magnetic field polarities are predicted as well as a 'low-energy' component for antiprotons below about 1 GeV.

Webber, W. R.↗
NASA NTRS1991

Spectral observations of the extreme ultraviolet background

The design of a grazing incidence spectrometer for measuring the diffusive extreme-ultraviolet astronomical background radiation is outlined, and the data obtained on the diffusive background between 80 and 650 A is discussed. The strongest emission line detected is solar backscattered He I 584 A radiation; solar 304 A radiation resonantly scattered by geocoronal He II is observed in both first and second order; and each of three remaining spectral features is found to be consistent with those expected from hot interstellar gas. Of these features, the strongest is the feature at 635 A identified as 630 A O v emission. A feature centered at about 99 A is fitted by a cluster of Fe XVIII and Fe XIX lines from gas at log T = 6.6-6.8, and a feature discovered near 178 A is found to be consistent with Fe X and Fe XI emission from gas at log T = 6.

Labov, Simon E.↗
NASA NTRS1992

Radio occultation observations of the ionospheres of Mars and Venus

The availability of a large body of radio occultation data for the Mars and Venus ionospheres makes possible comparative studies of their structures and temporal behavior. On Venus, the nightside ionosphere is produced by the transport of ionization from the dayside, which operates at solar maximum when the ionopause is high, and impact ionization by energetic electrons, which operates at all times. On Mars, transport from the dayside would seem to be inhibited for the same reason as for Venus at solar minimum, although sufficient flux of energetic electrons is present to generate nightside ionization. The Venus ionosphere at solar minimum, and that of Mars at all times, are not in a state of diffusive equilibrium above the chemical equilibrium regions.

Kliore, Arvydas J.↗
NASA NTRS1992

Constraints on the thermal evolution of Venus inferred from Magellan data

The impact craters with diameters from 1.5 to 280 km compiled from Magellan observations indicate that the crater population on Venus has a completely spatially random distribution and the size/density distribution of craters with diameters greater than or equal to 35 km is consistent with a 'production' population with an age of 500 plus or minus 250 m.y. The similarity in size distribution from area to area indicates that the crater distribution is independent of crater size. Also, the forms of the modified craters are virtually identical to those of the pristine craters. These observations imply that Venus reset its cratering record by global resurfacing 500 m.y. ago, and resurfacing declined relatively fast. The fact that less than 40 percent of all craters have been modified and that the few volcanically embayed craters are located on localized tectonic regions indicate that only minor and localized volcanism and tectonism have occurred since the latest vigorous resurfacing event approximately 500 m.y. ago and the interior of Venus has been solid and possibly colder than Earth's. This is because the high-temperature lithosphere of Venus would facilitate upward ascending of mantle plumes and result in extensive volcanism if the venusian upper mantle were as hot as or hotter than Earth's. Therefore, the present surface morphology of Venus may provide useful constraints on the pattern of that vigorous convection, and possibly on the thermal state of the venusian mantle. We examine this possibility through numerical calculations of three-dimensional thermal convection models in a spherical shell with temperature- and pressure-dependent Newtonian viscosity, temperature-dependent thermal diffusivity, pressure-dependent thermal expansion coefficient, and time-dependent internal heat production rate solar magnitude.

Arkani-Hamed, Jafar↗
NASA NTRS1995

Structure of mass-loading shocks. 2: Comparison of theory and observation at comet Halley

The multifluid diffusive model of G. P. Zank et al. (1994), which describes the interaction of the solar wind with a cometary plasma in the outer coma, has been used to model the structure of the Halley bow shock. The theoretical results are compared to in situ observations made by Giotto. We compare the solar wind and cometary ion number densities and pressures upstream and through the quasi-perpendicular and quasi-parallel shocks (observed on the inbound and outbound legs of the encounter, respectively). In general, good agreement is found between theory and observations in terms of shock structure, strength, and location, especially for the quasi-parallel shock. The comparison between tha quasi-perpendicular shock observations and theory is complicated by the apparently nonstationary behavior of the shock, a feature which has been remarked upon by other investigators. The cometary bow shock appears to be an excellent example of an energetic-particle-mediated shock where the energetic particles comprise less than 10% of the total number density.

Zank, G. P.↗
NASA NTRS1995

Evaluation of Thermal Control Coatings and Polymeric Materials Exposed to Ground Simulated Atomic Oxygen and Vacuum Ultraviolet Radiation

Numerous thermal control and polymeric samples with potential International Space Station applications were evaluated for atomic oxygen and vacuum ultraviolet radiation effects in the Princeton Plasma Physics Laboratory 5 eV Neutral Atomic Oxygen Facility and in the MSFC Atomic Oxygen Drift Tube System. Included in this study were samples of various anodized aluminum samples, ceramic paints, polymeric materials, and beta cloth, a Teflon-impregnated fiberglass cloth. Aluminum anodizations tested were black duranodic, chromic acid anodize, and sulfuric acid anodize. Paint samples consisted of an inorganic glassy black paint and Z-93 white paint made with the original PS7 binder and the new K2130 binder. Polymeric samples evaluated included bulk Halar, bulk PEEK, and silverized FEP Teflon. Aluminized and nonaluminized Chemfab 250 beta cloth were also exposed. Samples were evaluated for changes in mass, thickness, solar absorptance, and infrared emittance. In addition to material effects, an investigation was made comparing diffuse reflectance/solar absorptance measurements made using a Beckman DK2 spectroreflectometer and like measurements made using an AZ Technology-developed laboratory portable spectroreflectometer.

Kamenetzky, R. R.↗
NASA NTRS2002

Propagation of Secondary Antiprotons and Cosmic Rays in the Galaxy

Recent more accurate antiproton data obtained by the BESS team during the last solar minimum pose a challenge to conventional propagation models of cosmic rays. In particular, the diffusive reacceleration model, which matches well key secondary/primary isotope ratios in cosmic rays, fails to reproduce the secondary antiproton spectrum. Tuning both secondary/primary isotope ratios and antiprotons is possible, but requires artificial breaks in the diffusion coefficient and the injection spectrum of primaries. We will discuss some possibilities to overcome these difficulties in the propagation models. We will present new results of our calculation of CR propagation in the Galaxy using the GALPROP code.

Moskalenko, I. V.↗
NASA NTRS2002

The AstroBiology Explorer (ABE) MIDEX Mission Concept: Using Infrared Spectroscopy to Identify Organic Molecules in Space

One of the principal means by which organic compounds are detected and identified in space is by infrared spectroscopy. Past IR telescopic and laboratory studies have shown that much of the carbon in the interstellar medium (ISM) is in complex organic species but the distribution, abundance and evolutionary relationships of these materials are not well understood. The Astrobiology Explorer (ABE) is a MIDEX mission concept designed to conduct IR spectroscopic observations to detect and identify these materials and address outstanding problems in astrobiology, astrochemistry, and astrophysics. ABE's core science program includes observations of planetary nebulae and stellar outflows, protostellar objects, Solar System objects, and galaxies, and lines of sight through dense molecular clouds and the diffuse ISM. ABE is a cryogenically-cooled 60 cm diameter space telescope equipped with 3 cross-dispersed R-2000 spectrometers that share a single common slit. Each spectrometer measures one spectral octave and together cover the entire 2.5-20 micron region simultaneously. The spectrometers use state-of-the-art InSb and Si:As 1024x1024 pixel detectors. ABE would operate in a heliocentric, Earth drift-away orbit and have a core science mission lasting approximately 1.5 years. ABE is currently under study at NASA's Ames Research Center in collaboration with Ball Aerospace and Technologies Corp.

Sandford, Scott A.↗
NASA NTRS1976

Impulsive solar X-ray bursts. 4: Polarization, directivity and spectrum of the reflected and total bremsstrahlung radiation from a beam of electrons directed toward the photosphere

A Monte Carlo method is described for evaluation of the spectrum, directivity and polarization of X-rays diffusely reflected from stellar photospheres. the accuracy of the technique is evaluated through comparison with analytic results. Using the characteristics of the incident X-rays of the model for solar X-ray flares, the spectrum, directivity and polarization of the reflected and the total X-ray fluxes are evaluated. The results are compared with observations.

Langer, S. H.↗
NASA NTRS1979

Venus ionosphere - Photochemical and thermal diffusion control of ion composition

The major photochemical sources and sinks for ten of the ions measured by the ion mass spectrometer on the Pioneer Venus bus and orbiter spacecraft that are consistent with the neutral gas composition measured on the same spacecraft are identified. The neutral gas temperature (as a function of solar zenith angle) derived from measured ion distributions in photochemical equilibrium is given. Above 200 kilometers, the altitude behavior of ions is generally controlled by plasma diffusion, with important modifications for minor ions due to thermal diffusion resulting from the observed gradients of plasma temperatures. The dayside equilibrium distributions of ions are sometimes perturbed by plasma convection, while lateral transport of ions from the dayside seems to be a major source of the nightside ionosphere.

Bauer, S. J.↗