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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 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Thermal conductivity of earth materials at high temperatures.

The total thermal conductivity (lattice plus radiative) of several important earth materials is measured in the temperature range from 500 to 1900 K. A new technique is used in which a CO2 laser generates a low-frequency temperature wave at one face of a small disk-shaped sample, and an infrared detector views the opposite face to detect the phase of the emerging radiation. Phase data at several frequencies yield the simultaneous determination of the thermal diffusivity and the mean extinction coefficient of the material. The lattice, radiative, and total thermal conductivities are then calculated. Results for single-crystal and polycrystalline forsterite-rich olivines and an enstatite indicate that, even in relatively pure large-grained material, the radiative conductivity does not increase rapidly with temperature. The predicted maximum total thermal conductivity at a depth of 400 km in an olivine mantle is 0.020 cal/cm/sec/deg C, which is less than twice the surface value.

Schatz, J. F.↗
NASA NTRS1985

A theoretical study of the global F region for June solstice, solar maximum, and low magnetic activity

A time-dependent, three-dimensional, multi-ion model of the ionospheric F region at 120-800 km altitude is presented. Account is taken of field-aligned diffusion, cross-field electrodynamic drifts in equatorial and high latitude regions, interhemispheric flow, thermospheric winds, polar wind escape, energy-dependent chemical reactions and neutral composition changes. Attention is also given to the effects of ion production by solar EUV radiation and auroral precipitation, thermal conduction, diffusion-thermal heat flow, local heating and cooling processes, offsets between the geomagnetic and geographic poles, and bending of field lines near the magnetic equator. The model incorporates all phenomena described by previous models and can be applied to tracing magnetic storm and substorm disturbances from high to low latitudes on a global scale. Sample results are provided for ionospheric features during a June solstice, the solar maximum and in a period of low geomagnetic activity. The model will eventually be used to study coupled ionosphere-thermosphere activity.

Sojka, J. J.↗
NASA NTRS1967

Visualization of hydrogen fires.

Hydrogen fire visualization detection techniques including application of photography, TV and image converter in IR and UV regions

ULTRAVIOLET RADIATION↗
NASA NTRS1972

Gas-core reactor power transient analysis

The gas core reactor is a proposed device which features high temperatures. It has applications in high specific impulse space missions, and possibly in low thermal pollution MHD power plants. The nuclear fuel is a ball of uranium plasma radiating thermal photons as opposed to gamma rays. This thermal energy is picked up before it reaches the solid cavity liner by an inflowing seeded propellant stream and convected out through a rocket nozzle. A wall-burnout condition will exist if there is not enough flow of propellant to convect the energy back into the cavity. A reactor must therefore operate with a certain amount of excess propellant flow. Due to the thermal inertia of the flowing propellant, the reactor can undergo power transients in excess of the steady-state wall burnout power for short periods of time. The objective of this study was to determine how long the wall burnout power could be exceeded without burning out the cavity liner. The model used in the heat-transfer calculation was one-dimensional, and thermal radiation was assumed to be a diffusion process.

Kascak, A. F.↗
NASA NTRS1972

Analysis of inner and outer zone: OGO-1 and OGO-2 electron spectrometer and ion chamber data

The dynamic processes governing the acceleration and loss of electrons in the radiation zones are investigated. The radial diffusion coefficient was determined for a McIlwain parameter between 1.6 and 2.2 for electrons having a first adiabatic invariant of 12 MeV/gauss. The coefficient is larger than earlier values and suggests that there exists a lower limit to the fluxes in the inner zone. The agreement between observed and calculated magnetic fields and particle fluxes is improved by using solar wind pressure as input to the magnetic field models. Changes in the plasma pressure can cause apparent local time asymmetries in particle flux. A comparison of the magnetic field models with observed location of the trapping boundary also indicates the need for including distributed currents within the magnetosphere. The high latitude trapping boundary is only weakly dependent on A sub p, and the trapping boundary data are improved by including in the models a stand-off distance which varies with the plasma pressure.

Pfitzer, K. A.↗
NASA NTRS1972

Transition radiation as a source of cosmic X-rays.

It is shown that transition radiation generated during the passage of relativistic charged particles through interstellar grains can be an important source of cosmic X-rays. In order to account for recent X-ray observations below 300 eV by transition radiation, an energy density in interstellar space of about 10 eV per cu cm in 10 MeV electrons is required. This seems to rule out transition radiation as an important source of diffuse cosmic X-rays in any energy region.

Ramaty, R.↗
NASA NTRS1975

Characteristics of Jovian trapped electrons and protons for the region within 20 Jupiter radii and their interaction with Io

A brief summary is given of Pioneer 10 observations of trapped particles in the inner-core region (within 20 Jupiter radii) of the Jovian magnetosphere. The three sensor systems used to study trapped radiation in this region are described. Intensity profiles are plotted as a function of magnetic-shell parameter (L) for electrons with energies of at least 3 MeV, protons with energies of at least 35 MeV, and protons with energies between 0.5 and 1.8 MeV. The effect of trapped-particle absorption by Io is clearly seen in the intensity profiles of all the observed particle species, and evidence is presented for preferential absorption of small-pitch-angle particles by Io. Conclusive evidence is given for the fact that Jupiter's trapped radiation is maintained by the inward diffusion of particles across L shells.

Simpson, J. A.↗
NASA NTRS1976

Improved insulation material

Multilayer material consisting of embossed, silver-coated Mylar, nylon net, and silk net is useful for thermal-protection systems and cryogenic containers. Embossing serves two purposes: helps separate radiation barriers and controls radiant energy diffusion. Insulation requires no maintenance after installation.

Source record↗
NASA NTRS1978

A self-consistent model of a corotating Jovian magnetosphere

In the rotation-dominated model of the Jovian magnetosphere, proposed in the present paper, the plasma current distribution is dynamically consistent with the magnetic field. The model is constructed under the assumptions of an ionospheric plasma source without pitch angle scattering; loss-free radiation transport through flux tube interchange diffusion; and a static balance between centrifugal force and magnetic stress. Using these assumptions, a dynamic equation is derived for a self-consistent field configuration having a single adjustable parameter that is related to the plasma source strength. The equation is solved by an iterative technique. The self-consistent field resembles a radially distorted dipole field, rather than the flat magnetodisk configuration inferred from Pioneer data. The implication is that such a magnetodisk field would require an equatorial plasma source rather than a source at the feet of the field lines.

Carbary, J. F.↗
NASA NTRS1980

Investigation of the feasibility of CARS measurements in scramjet combustion

Results are presented of analytical and experimental investigations to determine the feasibility of using coherent anti-Stokes Raman Spectroscopy (CARS) to measure temperature and species concentration in supersonic combustion experiments. The CARS spectra of H2O, O2 and H2 were measured in laboratory flames. Computer code calculated spectra agree very well with the measured spectra. Temperature, and O2 and H2 concentration profiles have been determined from CARS spectra in a laboratory H2 air flat diffusion flame. Temperature measurements agree with radiation corrected thermocouple measurements within 5 to 10 percent, depending on species concentration. The feasibility of measuring O2 concentrations up to 10 percent, from the spectral shape was demonstrated. H2 concentrations determined from CARS intensities agree with spontaneous Raman measurements within a factor of two. Finally, a conceptual design was formulated for diagnostics in the Langley Research Center scramjet combustion facility.

Shirley, J. A.↗
NASA NTRS1981

A note on solar elevation dependence of clear sky snow albedo

Recent attempts to match shortwave albedo of snow for clear skies using approximate spectral solar fluxes and solutions of the radiative transfer equation for snow were unsuccessful until a separate surface reflection term was introduced. A separate consideration of specular reflection from surface snow grains has been objected to as being ad hoc. Results based on a new parameterization of shortwave radiation are discussed. Compared to the previous radiation models, new model gives higher diffuse insolation and predicts higher albedos. The difference between observed and predicted albedos is substantially reduced without invoking surface reflection.

Choudhury, B. J.↗
NASA NTRS1981

Very wide field camera

The study of galactic and faint extragalactic extended sources and peculiar ultraviolet objects by a very wide field of view camera, operated in the ultraviolet photometric and spectrometric modes is discussed. The photometric mode is direct photography through filters for observation of the following sources: (1) large scale distribution of ultraviolet radiation in the Milky Way; (2) diffusion of the galactic light above the galactic plane and in front of the large absorbing clouds; (3) the optical emission of the interstellar matter; (4) stars, and starlike objects with diameters less than 3 arc minutes. In the spectrometric mode (nebular spectrograph) the light from the center of the photometric field is concentrated on a slit covering 10 degrees by 10 arc minutes on the sky.

Courtes, G.↗
NASA NTRS1984

Magnetosphere, Rings, and Moons of Uranus

The observation of an ultraviolet aurora on Uranus implies the existence of a magnetosphere. It is suggested that the magnetospheres of Uranus and Saturn may be very similar. Charged particle sputtering of water ice surfaces on the Uranian moons may maintain an oxygen ion plasma torus similar to the heavy ion plasma torus at Saturn. Atmospheric cosmic ray albedo neutron decay may sustain an inner radiation belt with omnidirectional proton fluxes. If the 100 keV ion fluxes near 7 RU are similar to Saturnian ion fluxes at such energies, the Uranian aurora may be maintained by ion precipitation from the radiation belts at nearly the strong diffusion rate. This mechanism predicts comparable aurorae over both magnetic poles of Uranus, in contrast with the Faraday disc dynamo mechanism, which powers an aurora only over the sunlit pole of uranus. If, however, the 100 kev ion fluxes at Uranus are comparable to those at Saturn, any exposed methane ice surfaces on the moons and rings of Uranus would be quickly transformed by ion impacts to a black, carbonaceous polymer.

Cheng, A. F.↗
NASA NTRS1985

Nitridation of SiO2 for surface passivation

An attempt is made to relate the electrical properties of silicon dioxide film to the process history. A model is proposed to explain some of the observed results. It is shown that with our present knowledge of the dielectric, silicon dioxide film shows a lot of promise for its use in surface passivation, both for its resistance to impurity diffusion and for its resistance to radiation damage effects.

Lai, S. K. C.↗
NASA NTRS1984

APART/PADE analytical evaluation of the diffuse infrared background experiment for NASA's cosmic background explorer

The stray light performance of NASA's Diffuse Infrared Background Experiment (DIRBE) has been calculated using the APART/PADE code. That code has been upgraded to handle off-axis optical systems such as DIRBE. Under observing conditions, sunlight is attenuated by 21 to 29 orders-of-magnitude; uniform diffuse illumination, by 6 to 9 orders of magnitude. The sunlight is attenuated by multiple diffraction at an external sun shield and by a forebaffle at the entrance to the DIRBE. Stray light is nearly a linear function of the Bidirectional Reflectance Distribution Function (BRDF) of the primary mirror at all wavelengths - or it can be made to be so by reducing the size of the field defining stop from 0.866 to 0.7 degrees square. For uniform diffuse illumination, half of the stray radiation comes from within 5 degrees of the center of the field-of-view. Particulate contamination of the primary mirror is expected to be a problem and special polishing and cleaning procedures are recommended - before mirror overcoating and again before flight.

Evans, D. C.↗
NASA NTRS1986

A rapid and accurate method for calculation of stratospheric photolysis rates with molecular scattering

A method for calculating the photodissociation rates needed for photochemical modeling of the stratosphere, which includes the effects of molecular scattering, is described. The procedure is based on Sokolov's method of averaging functional correction. The radiation model and approximations used to calculate the radiation field are examined. The approximated diffuse fields and photolysis rates are compared with exact data. It is observed that the approximate solutions differ from the exact result by 10 percent or less at altitudes above 15 km; the photolysis rates differ from the exact rates by less than 5 percent for altitudes above 10 km and all zenith angles, and by less than 1 percent for altitudes above 15 km.

Boughner, Robert E.↗