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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Development of a triaxially formed fabric for use in an improved restraint layer in the shuttle space suit

A series of materials for use as an improved restraint layer in the shuttle space suit was developed. The feasibility of weaving triaxial fabrics in tight, low porosity configurations with yarns of appropriate sizes and materials was demonstrated along with the stability and isotropy of triaxial fabrics. The triaxial fabric constructions, BP44P and BP40M, can be reproduced on a production basis. Both fabric constructions afford excellent strength-to-weight ratio and exhibit improved tear strength and shear resistance over biaxial fabrics.

Source record↗
NASA NTRS1977

Test particle propagation in magnetostatic turbulence. 3: The approach to equilibrium

The asymptotic behavior, for large time, of the quasi-linear diabatic solutions and their local approximations is considered. A time averaging procedure is introduced which yields the averages of these solutions over time intervals which contain only large time values. A discussion of the quasi-linear diabatic solutions which is limited to those solutions that are bounded from below as functions of time is given. It is shown that as the upper limit of the time averaging interval is allowed to approach infinity the time averaged quasi-linear diabatic solutions must approach isotropy (mu-independence). The first derivative with respect to mu of these solutions is also considered. This discussion is limited to first derivatives which are bounded functions of time. It is shown that as the upper limit of the time averaging interval is allowed to approach infinity, the time averaged first derivative must approach zero everywhere in mu except at mu = 0 where it must approach a large value which is calculated. The impact of this large derivative on the quasi-linear expansion scheme is discussed. An H-theorem for the first local approximation to the quasi-linear diabatic solutions is constructed. Without time averaging, the H-theorem is used to determine sufficient conditions for the first local approximate solutions to asymptote, with increasing time, to exactly the same final state which the time averaged quasi-linear diabatic solutions must approach as discussed above.

Klimas, A. J.↗
NASA NTRS1976

Interplanetary magnetic field power spectra - Mean field radial or perpendicular to radial

A detailed frequency analysis of Pioneer-6 interplanetary magnetic field data is carried out for 5 to 15 hour periods during which the mean interplanetary field is approximately radial or perpendicular to radial. The reason why these data sets were chosen is that by making the usual assumption that the phase speed of any wave present is much less than the mean solar wind speed, the measured frequency spectra can be interpreted in terms of the wave number parallel or perpendicular to the mean field, without such additional assumptions as isotropy or the dominance of a particular mode and without measurements of velocity and density. The details of the calculation of the magnetic field power spectra, coherencies, and correlation functions are discussed, along with results obtained directly from the data (such as spectra, slopes, anisotropies, and coherencies). The results are interpreted in terms of MHD theory, and are related to work in other areas.

Sari, J. W.↗
NASA NTRS1977

Consequences of using nonlinear particle trajectories to compute spatial diffusion coefficients

In a study of cosmic ray propagation in interstellar and interplanetary space, a perturbed orbit resonant scattering theory for pitch angle diffusion in a slab model of magnetostatic turbulence is slightly generalized and used to compute the diffusion coefficient for spatial propagation parallel to the mean magnetic field. This diffusion coefficient has been useful for describing the solar modulation of the galactic cosmic rays, and for explaining the diffusive phase in solar flares in which the initial anisotropy of the particle distribution decays to isotropy.

Goldstein, M. L.↗
NASA NTRS1977

Spectra and angular distributions of atmospheric gamma rays from 0.3 to 10 MeV at lambda = 40 deg

Measurements of the spectral and angular distributions of atmospheric gamma sq cm rays in the energy range 0.3-10 MeV over Palestine, Texas, at residual depths of 2.5 and 70 g/sq cm are reported. In confirmation of the general features of a model prediction, the measurements show at 2.5 g/sq cm upward moving fluxes greater than the downward moving fluxes, the effect increasing with energy, and approximate isotropy at 70 g/sq cm. Numerous characteristic gamma-ray lines were observed, most prominently at 0.511, 1.6, 2.3, 4.4, and 6.1 MeV. Their intensities were also compared with model predictions. Observations were made with an actively shielded scintillator counter with two detectors, one of aperture 50 deg FWHM and the other of 120 deg FWHM. Above 1 MeV, contributions to the counting rate from photons penetrating the shield annulus and from neutron interactions were large; they were studied by means of a Monte Carlo code and are extensively discussed.

Ling, J. C.↗
NASA NTRS1977

Large eddy simulation of homogeneous isotropic turbulence

This paper presents results from a comprehensive investigation of large-eddy simulations of homogeneous isotropic turbulence. Calculations have been made using grid meshes, a number of flowfield filters, and two simple subgrid scale turbulence models. Particular attention has been paid to the degree of isotropy and the ability of the approach to predict higher-order statistical quantities (skewness and flatness). Directions for needed improvement in the simulation approach are indicated, and a plea is made to experimenters to process their data in a way which will facilitate comparison with large eddy simulations.

Ferziger, J. H.↗
NASA NTRS1978

Future directions in experimental gamma ray astronomy

Better vehicles and instruments are needed if gamma ray spectroscopy in astrophysics and cosmology is to advance. A gamma ray observatory will (1) permit long-term observations of selected sources to measure their variability and to achieve high sensitivity; (2) measure periods in days or weeks; and (3) assess the entire sky to observe various predicted sources, to measure the energy spectrum, and to map the isotropy of the cosmic ray background over larger collecting areas (of the order of a square meter). Conventional and unconventional instruments must cover the energy range from 0.1 MeV to 20 MeV with improved sensitivity. Angular resolution must be improved one degree or more to study discrete X-ray sources in the galactic center. Actively collimated detectors, improved double Compton instruments, and gamma ray correlators to actively synthesize the absolute energy spectrum of the sky protons are discussed as well as the need for scientific balloons.

Haymes, R. C.↗
NASA NTRS1977

Magnetic fields greater than 10 to the 20th power gauss

Zaumen (1976) found that spontaneous pair production in a uniform magnetic field should be a feasible process for field strengths at least of the order of 10 to the 20th power gauss. This note points out that a magnetic field of this order of magnitude is most unlikely to occur in realistic astrophysical situations because of the large dynamical and quantum-mechanical effects such a field would produce. It is suggested that Zaumen's calculation would probably have little bearing on the suspected evolution of astrophysical systems since other processes (either dynamical or quantum-mechanical) apparently limit the field strength before such high magnetic fields would be reached. An upper limit of about 10 to the 16th power gauss is obtained by considering the isotropy of the 3-K blackbody radiation, the formation of collapsed objects in very high magnetic fields, and magnetic bremsstrahlung processes in quantum electrodynamics.

Lerche, I.↗
NASA NTRS1978

The UCSD/MIT hard X-ray and low energy gamma-ray experiment for HEAO-1 - Design and early results

Primary scientific objectives of the experiment are the measurement of the spectra and time variations of discrete sources and the spectrum and isotropy of the diffuse background, all in the 10 keV to 10 MeV energy range. The instrument consists of an array of 7 NaI(Tl)/CsI(Na) phoswich-type detectors and 8 large CsI(Na) shields. In order to achieve the maximum sensitivity allowed by weight, data rate and funding constraints of the mission, three detector and aperture geometries were selected. The instrument's total sensitive area is 494 sq cm. The fields of view vary from 1.7 deg x 20 deg FWHM at low energies to 43 deg FWHM at high energies. The basic instrument concepts, details of the mechanical and electrical design, and pre-launch calibrations are presented. In-orbit performance is described and background measurements are analyzed and used to estimate the experiment's ultimate sensitivity.

Matteson, J. L.↗
NASA NTRS1978

The cosmic gamma-ray background from the annihilation of primordial stable neutral heavy leptons

The spectra and intensities of gamma radiation from (1) a homogeneous cosmic lepton background (2) a possible lepton halo around the Galaxy, and (3) integrated background radiation from possible lepton halos around other galaxies and from rich galaxy clusters are examined. Heavy-lepton annihilation radiation from the halos of other galaxies accounts for at most 0.005 of the background intensity, and the radiation from rich clusters account for at most 0.00005 of the background intensity. It is suggested that lepton annihilation fluxes from a galactic halo would be confused with cosmic-ray produced radiation and would therefore be difficult to observe. Radiation from a homogeneous cosmological lepton background might account for approximately 0.0001 of the observed cosmic gamma ray background. Energy spectrum and isotropy are considered.

Stecker, F. W.↗
NASA NTRS1977

Turbulence simulation mechanization for Space Shuttle Orbiter dynamics and control studies

The current version of the NASA turbulent simulation model in the form of a digital computer program, TBMOD, is described. The logic of the program is discussed and all inputs and outputs are defined. An alternate method of shear simulation suitable for incorporation into the model is presented. The simulation is based on a von Karman spectrum and the assumption of isotropy. The resulting spectral density functions for the shear model are included.

Tatom, F. B.↗
NASA NTRS1979

Unified field theories, the early big bang, and the microwave background paradox

It is suggested that a superunified field theory incorporating gravity and possessing asymptotic freedom could provide a solution to the paradox of the isotropy of the universal 3K background radiation. Thermal equilibrium could be established in this context through interactions occurring in a temporally indefinite preplanckian era.

Stecker, F. W.↗
NASA NTRS1979

Spectrophotometry of Michigan-Tololo quasars

Emission-line quasar characteristics are confirmed for 80% of the objects observed, including at least four new quasars with spectral features indicative of supernova-like outflow. Approximately 73% of the redshifts predicted from the discovery plates are found accurate with a mean error in z of 0.03, and a large range of z (from about 0.1 to 3.16) is represented in the sample. The observed redshift distribution for quasars is marginally consistent with a constant co-moving quasar density above z approximately 2.0. The shape of the redshift distribution may be used as an isotropy probe with a cosmic time resolution of a few times one-hundred million years in the early universe; therefore, continued surveys of this sort are important even if accurate magnitudes are not determined.

Lewis, D. W.↗
NASA NTRS1978

Inhomogeneity in cosmological element formation

Cosmological deuterium production is sensitive to variations from the homogeneity which is assumed in standard cosmological models. We demonstrate that a wide range of possible variations in primordial shearing velocity fields can produce deuterium with an abundance comparable to (or exceeding) the observed value even in closed models, without greatly altering the production of helium or appreciably distorting the isotropy of the microwave background radiation.

Olson, D. W.↗
NASA NTRS1978

Opacified silica reusable surface insulation /RSI/ for thermal protection of the Space Shuttle Orbiter

A reusable surface insulation (RSI) material adopted for use on limited areas of the Orbiter's heat shield is described. The RSI is a rigid sintered fibrous silica material containing about 3% by weight of 1200-grit silicon carbide powder. RSI manufacture is described; strength characteristics and thermal conductivity of the final product can be tailored by controlling the isotropy, and the density, coefficient of thermal expansion, and specific heat are reported. Data establishing that opacification of RSI with silicon carbide lowers the thermal conductivity are presented.

Goldstein, H. E.↗
NASA NTRS1978

Cosmic diffuse gamma-rays at medium energies

Cosmic diffuse gamma-ray fluxes have been measured in six energy intervals from 2 to 25 MeV with a balloon-borne gamma-ray telescope. It is found that the observed fluxes are compatible with an energy distribution of 0.0265 times E to the -2.08 (photon/sq cm-s-sr-MeV) at lower energies and steepen at higher energies to meet a power law of 0.017 (E/MeV) to the -2.4. No deviation of the gamma-ray flux from isotropy is observed for five different times during the balloon flight for 10-deg intervals up to 50 deg from the zenith and at celestial coordinates varying from latitude -27 deg, longitude 102 deg to latitude 56 deg, longitude 195 deg, excluding the region in the galactic-anticenter direction. Upper limits to fluxes of 3-25-MeV gamma rays are deduced for a number of possible galactic and extragalactic sources.

White, R. S.↗
NASA NTRS1979

Gradient and curvature drifts in magnetic fields with arbitrary spatial variation

It is shown that, for a magnetic field of arbitrary spatial variation, a nearly isotropic distribution of charged particles drifts with a velocity given by the usual first-order orbit theory drifts averaged over pitch angle. It is assumed that the near-isotropy brought about by scattering, but conclusions concerning drift are insensitive to the details of the scattering process. It is found that this drift velocity is correct even for arbitrarily large ratios of particle gyroradius to magnetic spatial scale, although this velocity must, like all drift effects, be viewed on a scale larger than a gyroradius. Hence for many astrophysical applications, such as cosmic rays, where anisotropies are small, the usual drift velocities provide a valid approximation to convective motions even if the magnetic field scales are very small.

Isenberg, P. A.↗
NASA NTRS1980

Fluctuations in the microwave background at large angular scale

The measurements of fluctuations in the cosmic microwave background are shown to be consistent with the first order anisotropy at the level of about one part in a thousand and the limits of about one part in three thousand for fluctuations on any other scale. It is suggested that the first order anisotropy is due to the motion of the solar system relative to the radiation. This interpretation is evidence supporting the Cosmological Principle. The observed isotropy of the cosmic microwave background contradicts the concept of an indefinite hierarchy of clustering in the universe.

Smoot, G. F.↗