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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 361 records · Page 20
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NASA NTRS1976

Successful large-scale use of CMOS devices on spacecraft traveling through intense radiation belts

This paper describes the environmental models of the radiation belts and computational techniques which have been developed for predicting the radiation hazards for spacecraft. These data and techniques are then applied to the Atmosphere Explorer 51 spacecraft to explain its successful survival for more than 18 months in a severe environment. In particular, the results of the analysis are used to explain the performance of some 2400 CMOS devices, and consequently, they demonstrate the reliability of this device technology in spacecraft systems.

Brucker, G. J.↗
NASA NTRS1975

IMP 6, 7 and 8 observations of the composition and time variations of low energy cosmic rays

The charge composition and time variations of quiet-time cosmic rays in the energy range 10 to 25 MeV/nucleon were studied to determine the source of the enhancement of quiet-time intensities of low energy nitrogen and oxygen nuclei observed by Pioneer 10. Time variations were established from data from IMPs 6, 7, and 8; the charge composition was obtained by summing data from IMP 7 and IMP 8. The neon to carbon ratio present in solar rays is too low to explain an observed enhancement of neon. Helium and oxygen have the same percentage modulation for a range of x5 in intensity. This can be explained within the framework of the field-force approximation and the selection mechanism based on the first ionization potential proposed by Fisk et al. (1974) if both oxygen and helium are singly charged.

Von Rosenvinge, T. T.↗
NASA NTRS1975

The effect of adiabatic focusing upon charged particle propagation in random magnetic fields

This paper describes the effects of strong adiabatic focusing in terms of eigenfunctions of an operator which incorporates both scattering by random fields and focusing by a spatially inhomogeneous guiding field. It is found that focused transport differs from rectilinear transport in the following ways: (1) the coherent velocity toward stronger fields is larger than that toward weaker fields; (2) coherent effects are more prominent relative to diffusive effects when focusing is present; and (3) initial anisotropies at injection have a minimal influence upon rectilinear transport but they have a pronounced effect on focused transport. These features explain certain well-known discrepancies between the diffusive picture and the observed profiles of solar particle events. In particular, they explain the so-called scatter-free propagation of kilovolt flare electrons.

Earl, J. A.↗
NASA NTRS1975

Search for a particle with a long interaction length

A search has been carried out for a long-lived particle having an interaction length lambda sub m equals 300 to 2000 gm/sq cm in air. Such a particle, called the mandela, has been proposed to explain an anomalous energy spectrum of particles observed near sea level with a shallow spectrometer. Data taken at mountain altitude with a deep spectrometer has been examined for compatibility with the existence of the mandela. Although data tend to favor the mandela hypothesis the results are not conclusive and appear to be explainable by conventional means.

Barrowes, S. C.↗
NASA NTRS1976

Random processes as a cause of the lunar asymmetry

The offset of the center of mass of the moon from its center of figure together with moment of inertia differences are explainable by a lunar crust of randomly varying thickness. The necessity of postulating a method of preferential material transport into a particular lunar hemisphere to explain the lunar asymmetry is eliminated.

Kobrick, M.↗
NASA NTRS1976

A model for the X-ray nova A0620-00

A model is proposed for the transient X-ray source A0620-00 involving a white dwarf accreting mass from a late-type subgiant companion. The transient behavior of the X-ray source is explained by the instability to mass loss of the companion (as in Algol-type binaries). The brightening, spectrum, and decay timescale of the optical counterpart are explained in terms of re-emission of X-radiation intercepted by the subgiant. A0620-00 should provide an excellent test case for numerical models of stellar atmospheres irradiated by an external X-ray flux.

Endal, A. S.↗
NASA NTRS1977

Data representations in PDP-10 MacLISP

The internal representations of the various MacLISP data types are presented and discussed. Certain implementation tradeoffs are considered. The ultimate decisions on these tradeoffs are discussed in the light of MacLISP's prime objective of being an efficient high-level language for the implementation of large systems such as MACSYMA. The basic strategy of garbage collection is outlined, with reference to the specific representations involved. Certain clever tricks are explained and justified. The address space crunch is explained and some alternative solutions explored.

Steele, G. L., Jr.↗
NASA NTRS1976

Meter-wavelength VLBI. IV - Temporal and spatial scattering of the Crab Nebula pulsar's radiation

The spatial and temporal phenomena observed in the Crab Nebula pulsar's radiation are reviewed, with emphasis on the recent VLBI observations of the apparent angular size and the ratio of pulsing to total power. Three models for scattering (single thin screen, two screen, and extended medium) are discussed and shown to be deficient, under the usual assumption of a uniform scattering medium, in explaining the observed combination of temporal and angular broadening. A new model is proposed, in which the temporal broadening is dominated by scattering in the small filament which lies in the nebula in front of the pulsar, while the extended interstellar medium causes the angular broadening. This model explains the otherwise discordant angular and temporal effects and also the lack of an apparent source-size expansion with pulse phase.

Vandenberg, N. R.↗
NASA NTRS1976

Simultaneous Pc 1 observations by the synchronous satellite ATS-1 and ground stations - Implications concerning IPDP generation mechanisms

Results are presented for an experimental study designed to examine the properties of Pc 1 activity observed simultaneously at ATS 1 and two Canadian ground stations. The Pc 1 activity is found to follow substorm expansion phase onsets and to occur most frequently at dusk. Dynamic spectra waves at both ground stations are that of IPDP (Intervals of Pulsations Diminishing by Period) type Pc 1. A previously proposed mechanism to explain IPDP generation, which required a rapid increase in the equatorial magnetic field to produce IPDP, is inconsistent with the dynamic spectra and magnetic field observations. Either purely azimuthal or a combination of azimuthal and radial inward drift of energetic resonant protons is an equally plausible mechanism to explain IPDP generation.

Bossen, M.↗
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 NTRS1976

On the source of the ancient lunar magnetic field

Analysis of the returned samples, surface observations, and the orbital surveys reveal the presence of a widespread magnetism on the lunar surface but no global field. In the light of Runcorn's proof that internally generated fields do produce magnetization patterns in a spherical crust whose magnetic field lines are confined to within the crust, the above fact is explained in terms of an ancient lunar dynamo which magnetized the lunar crust and then disappeared. The possibility of ancient uniform magnetization by an external field is ruled out, for such magnetization would have been erased as the moon warmed up due to radioactive decay. Although the terrestrial field model is consistent with the measurements, this possibility is also ruled out, because the moon would have had to remain close to earth for about one billion years. The direction of the present magnetization is not predominantly north-south, but is radial and east-west, a fact explained by the assumption that the ancient lunar magnetic dipole moment was not along the present rotation axis.

Russell, C. T.↗
NASA NTRS1977

What quenches the helium shell flashes

An analysis is conducted of a typical stellar helium shell flash cycle. A sequence of 12 flashes for a population I star is considered. The changes taking place at a constant mass layer in the helium-burning shell are studied as the flash develops. A highly simplified mathematical description is presented, taking into account the three necessary conditions for the occurrence of the flash and the pressure-density and temperature-density relationships. Quantities which are helpful in explaining what triggers the flash are found to be useful in explaining what quenches the flash.

Sackmann, I.-J.↗
NASA NTRS1977

The 5-day wave and ionospheric absorption

In a previous paper, Fraser and Thorpe (1976) indicated that the average partial-coherence spectra for three summers and the average for three winters at a southern mid-latitude site had a dominant peak at a period of about six days. This peak in coherence between absorption and temperature is anomalous, and the present paper explains how some of the unexpected coherence features can be explained by the five-day wave described by Geisler and Dickinson (1976) and whose existence in the upper stratosphere was discussed by Rodgers (1976).

Fraser, G. J.↗
NASA NTRS1977

The low-latitude circulation of Mars

A steady-state two-layer atmospheric model is used in an attempt to simulate the circulation of the equatorial regions of Mars, with consideration of both thermal and mechanical orographic effects. A steady-state solution is sought with the aim of producing mean seasonal circulations upon which tides can be superimposed, and the relative importance of orographic forcing at low latitudes is evaluated. It is assumed that the atmospheres over a topographic feature and over flat terrain possess the same radiative and convective properties, simple dissipation laws are introduced which represent a surface drag effect, and six first-order difference equations are obtained and then reduced to two linear complex second-order coupled difference equations. Analysis of the response of the equinoctial basic wind field to a Gaussian orographic feature situated at the equator and zero deg longitude reveals a number of similarities and differences between the Martian and terrestrial responses. Most of the similarities are explained in terms of the dynamics of a rotating atmosphere, while the major differences are at least partially explained by the different optical properties, lower boundaries, and smaller mass of the Martian atmosphere.

Webster, P. J.↗
NASA NTRS1977

The tilt effect for Saturn's rings

Multiple-scattering computations are carried out to explain the variation of the observed brightness of the A and B rings of Saturn with declination of the earth and sun. These computations are performed by a doubling scheme for a homogeneous plane-parallel scattering medium. A range of choices is tested for the phase function, albedo for single scattering, and optical depth of both the rings. Isotropic scattering and several other simple phase functions are ruled out, and it is found that the phase function must be moderately peaked in both the forward and backward directions. The tilt effect can be explained by multiple scattering in a homogeneous layer, but, for ring B, this requires a single-scattering albedo in excess of 0.8. The brightest part of ring B must have an optical depth greater than 0.9. It is found that the tilt effect for ring A can be reproduced by particles having the same properties as those in ring B with the optical depth for the A ring in the range 0.4 to 0.6.

Esposito, L. W.↗
NASA NTRS1977

Model of climate evolution based on continental drift and polar wandering

The thermodynamic meteorologic model of Adem is used to trace the evolution of climate from Triassic to present time by applying it to changing geography as described by continental drift and polar wandering. Results show that the gross changes of climate in the Northern Hemisphere can be fully explained by the strong cooling in high latitudes as continents moved poleward. High-latitude mean temperatures in the Northern Hemisphere dropped below the freezing point 10 to 15 m.y. ago, thereby accounting for the late Cenozoic glacial age. Computed meridional temperature gradients for the Northern Hemisphere steepened from 20 to 40 C over the 200-m.y. period, an effect caused primarily by the high-latitude temperature decrease. The primary result of the work is that the cooling that has occurred since the warm Mesozoic period and has culminated in glaciation is explainable wholly by terrestrial processes.

Donn, W. L.↗
NASA NTRS1978

Atmospheric-wake vortex interactions

The interactions of a vortex wake with a turbulent stratified atmosphere are investigated with the computer code WAKE. It is shown that atmospheric shear, turbulence, and stratification can provide the dominant mechanisms by which vortex wakes decay. Computations included the interaction of a vortex wake with a viscous ground plane. The observed phenomenon of vortex bounce is explained in terms of secondary vorticity produced on the ground. This vorticity is swept off the ground and advected about the vortex pair, thereby altering the classic hyperbolic trajectory. The phenomenon of the solitary vortex is explained as an interaction of a vortex with crosswind shear. Here, the vortex having the sign opposite that of the sign of the vorticity in the shear is dispersed by a convective instability. This instability results in the rapid production of turbulence which in turn disperses the smoke marking the vortex.

Bilanin, A. J.↗
NASA NTRS1976

Studies on color-center formation in glass utilizing measurements made during 1 to 3 MeV electron irradiation

The coloring of NBS 710 glass was studied using a facility for making optical absorption measurements during and after electron irradiation. The induced absorption contains three Gaussian shaped bands. The color center growth curves contain two saturating exponential and one linear components. After irradiation the coloring decays can be described by three decreasing exponentials. At room temperature both the coloring curve plateau and coloring rate increases with increasing dose rate. Coloring measurements made at fixed dose rate but at increasing temperature indicate: (1) The coloring curve plateau decreases with increasing temperature and coloring is barely measurable near 400 C. (2) The plateau is reached more rapidly as the temperature increases. (3) The decay occurring after irradiation cannot be described by Arrhenius kinetics. At each temperature the coloring can be explained by simple kinetics. The temperature dependence of the decay can be explained if it is assumed that the thermal untrapping is controlled by a distribution of activation energies.

Swyler, K. J.↗