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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Geomagnetic field distortions and their effects on radiation belt particles.

One of the quadrupole terms in the main geomagnetic field is found to contribute to a north-south 'shear distortion' of the particle-drift shells, whereas one of the octupole components causes a longitude-dependent radial deformation and associated 'drift-shell splitting.' The collective action of all higher multipoles on trapped-particle motion is then used to analyze the 'true' anomalies or distortions of the internal geomagnetic field that are independent of the quadrupole-related eccentricity of the main dipole. These 'true' anomalies must originate in upper-mantle or crustal perturbations that lie relatively near the earth's surface on both sides of the mid-Atlantic ridge; they influence trapped-particle drift shells only where the latter have their closest approach to the earth (South Atlantic and South African areas). The quadrupole and octupole perturbations, on the other hand, obviously originate deep in the earth's core. In the final part of this review, we discuss the effects of external magnetospheric currents. A time-dependent symmetric ring current causes drift shells to be displaced radially, with associated particle acceleration; magnetopause currents introduce a day-night asymmetry, causing shell splitting.

Roederer, J. G.↗
NASA NTRS1972

UK-5 Van Allen belt radiation exposure: A special study to determine the trapped particle intensities on the UK-5 satellite with spatial mapping of the ambient flux environment

Vehicle encountered electron and proton fluxes were calculated for a set of nominal UK-5 trajectories with new computational methods and new electron environment models. Temporal variations in the electron data were considered and partially accounted for. Field strength calculations were performed with an extrapolated model on the basis of linear secular variation predictions. Tabular maps for selected electron and proton energies were constructed as functions of latitude and longitude for specified altitudes. Orbital flux integration results are presented in graphical and tabular form; they are analyzed, explained, and discussed.

Stassinopoulos, E. G.↗
NASA NTRS1973

Low frequency gyro-synchrotron radio noise from the earth's outer radiation belt

The problem of detecting cyclotron and synchrotron noise from superthermal electrons is analyzed for the frequency range 30 kHz 300 kHz. Due to the earth's ionosphere, ground based observation of this noise is improbable. Therefore, the calculations are made for an observer in the interplanetary medium. In particular, the location is chosen in the geomagnetic equatorial plane at a geocentric distance of 32 earth radii. This position of the observer allows the theoretical results to be compared directly with data obtained from the radio astronomy experiment aboard the IMP-6 spacecraft.

Frankel, M. S.↗
NASA NTRS1973

Jupiter's radiation belts - Can Pioneer 10 survive

Recent calculations suggest that three of the Galilean satellites are very effective in limiting the fluxes of energetic electrons and protons diffusing inward from Jupiter's outer magnetosphere. Electron and proton densities with and without lunar effects are plotted as functions of the distance from the center of the planet in units of Jupiter radii. Both electrons and protons in the model come from the solar wind. The trajectory of Pioneer 10 in magnetic coordinates is examined and the period of greatest danger to the spacecraft is discussed.

Hess, W. N.↗
NASA NTRS1974

Jupiter radiation belt models (July 1974)

Flux profiles which were derived from data returned by Pioneer 10 during Jupiter encounter, form the basis for a new set of numerical models for the energy spectra of electrons and protons in Jupiter's inner magnetosphere.

Divine, N.↗
NASA NTRS1975

Radiation belts of Jupiter - A second look

The outbound leg of the Pioneer 11 Jupiter flyby explored a region farther from the equator than that traversed by Pioneer 10, and the new data require modification or augmentation of the magnetodisk model based on the Pioneer 10 flyby. The inner moons of Jupiter are sinks of energetic particles and sometimes sources. A large spike of particles was found near Io. Multiple peaks occurred in the particle fluxes near closest approach to the planet; this structure may be accounted for by a complex magnetic field configuration. The decrease in proton flux observed near minimum altitude on the Pioneer 10 flyby appears attributable to particle absorption by Amalthea.

Fillius, R. W.↗
NASA NTRS1980

21 cm maps of Jupiter's radiation belts from all rotational aspects

Two-dimensional maps of the radio emission from Jupiter were made in December 1977 at a frequency of 1,412 MHz using the Westerbork telescope. Pictures in all four Stokes parameters have been obtained every 15 deg in longitude, each smeared over 15 deg of the planet's rotation. The maps have an E-W resolution of about 1/3 of the diameter of the disk and a N-S resolution 3 times less. The total intensity and linear polarization maps are accurate to 0.5% and the circularly polarized maps to 0.1% of the maximum intensities in I. The whole set of maps clearly shows the existence of higher order terms in the magnetic field of Jupiter.

De Pater, I.↗
NASA NTRS1983

Radial diffusion in Saturn's radiation belts - A modeling analysis assuming satellite and ring E absorption

A modeling analysis is carried out of six experimental phase space density profiles for nearly equatorially mirroring protons using methods based on the approach of Thomsen et al. (1977). The form of the time-averaged radial diffusion coefficient D(L) that gives an optimal fit to the experimental profiles is determined under the assumption that simple satellite plus Ring E absorption of inwardly diffusing particles and steady-state radial diffusion are the dominant physical processes affecting the proton data in the L range that is modeled. An extension of the single-satellite model employed by Thomsen et al. to a model that includes multisatellite and ring absorption is described, and the procedures adopted for estimating characteristic satellite and ring absorption times are defined. The results obtained in applying three representative solid-body absorption models to evaluate D(L) in the range where L is between 4 and 16 are reported, and a study is made of the sensitivity of the preferred amplitude and L dependence for D(L) to the assumed model parameters. The inferred form of D(L) is then compared with that which would be predicted if various proposed physical mechanisms for driving magnetospheric radial diffusion are operative at Saturn.

Hood, L. L.↗
NASA NTRS1985

Precipitation of radiation belt electrons by man-made waves A comparison between theory and measurement

The temporal and spectral shape and the absolute flux level of particle pulses precipitated by a VLF transmitter are examined from a theoretical point of view. A test-particle model of the gyroresonant wave-particle interaction is applied to the parameters of the observed cases for calculating the precipitation characteristics. The temporal shapes of the precipitation pulses are found to be controlled (1) by the pitch angle dependence of the particle distribution near the edge of the loss cone and (2) by the multiple interaction of the particles with the waves due to significant atmospheric backscatter.

Inan, U. S.↗
NASA NTRS1988

Limiting energy spectrum of a saturated radiation belt

The condition for magnetospheric wave growth in the presence of anisotropic charged particle distributions is used to extend the Kennel-Petschek theory that traditionally imposes an upper bound on the integral flux of charged particles at energies above a certain threshold to provide a limit on the differential flux at any energy above this threshold. A closed-form expression is derived for the limiting energy spectrum consistent with marginal occurrence of a magnetospheric maser at all wave frequencies below a certain fraction of the electron or proton gyrofrequency. The bounded integral can be recast in such a way that repeated differentiations with respect to v(parallel) actually generate a closed expression for the limiting form of the velocity space distribution, and thus for the limiting energy spectrum of the corresponding particles, whenever the anisotropy parameter is an integer.

Schulz, Michael↗
NASA NTRS1987

Whistler mode emissions in the Uranian radiation belts

Voyager 2 detected intense whistler mode emissions and fluxes of energetic electrons during the outbound pass through the region of auroral L shells. The observed energetic (E greater than 22 keV) electron distribution, a model warm (E less than 27.5 keV) electron distribution, and the cold plasma density profile deduced by Kurth et al. (1987) are used to calculate the ray path-integrated spatial amplification of whistlers which arrive at Voyager 2 from the magnetic equator. By matching the calculated amplification and the relative gains at different frequencies deduced from the observed whistler power spectrum, the pitch angle anisotropy parameters of the electron distributions are determined to within a fairly narrow range of values. The estimated bounce average pitch angle diffusion coefficient indicates that electrons are on strong diffusion over a wide range in energies. The electron precipitation energy flux is sufficient to produce the observed auroral light emissions.

Coroniti, F. V.↗