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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 1,657 records · Page 92
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NASA NTRS1979

Initial Pioneer Venus magnetometer observations

Initial Pioneer Venus magnetometer observations reveal a highly dynamic interaction between the solar wind and the ionosphere and a very weak and possibly absent intrinsic magnetic field. The bow shock position and the altitude of the ionopause vary markedly from day to day. The magnetic pressure in the magnetosheath just outside the ionopause is in near balance with the thermal ionospheric pressure inside. Although the ionospheric magnetic field strength is generally low, occasional enhancements are observed with field strengths exceeding that in the magnetosheath. These bundles of magnetic flux, or flux ropes, may be convected to the night side ionosphere in which large field strengths (compared to the dayside) are common. The magnetic field magnitude and direction in this region are quite variable, suggesting that the field is not due to an intrinsic planetary source, but rather due to induced ionospheric currents. The magnetic moment is probably much less than 10 to the 22nd Gauss-cu cm.

Russell, C. T.↗
NASA NTRS1980

Aspects of pulsar evolution

Pulsar statistics are examined from the point of view of generalized evolutionary equations that assume that pulsar torques diminish exponentially with a decay-time constant T, to be determined empirically. Decay or alignment of the neutron-star magnetic moment, or a combination, may cause the torque to diminish with time. The Sturrock-Ruderman-Sutherland pair-production model provides a quantitative way to calculate pulsar lifetimes. Different tests, which use the data in partially independent ways and involve different assumptions, consistently suggest that T is less than a million years and may be as short as several hundred thousand years. The distribution of pulsars, and of those with more than 5% missing pulses is quantitatively consistent with pair production threshold, when the variation of this threshold with neutron star mass is taken into account.

Fujimura, F. S.↗
NASA NTRS1979

Accretion by rotating magnetic neutron stars. III - Accretion torques and period changes in pulsating X-ray sources

The solutions of the two-dimensional hydromagnetic equations are used to calculate the torque on a magnetic neutron star accreting from a Keplerian disk. It is found that the magnetic coupling between the star and the plasma in the outer transition zone is appreciable; that as a result, the spin-up torque on fast rotators is substantially less than that on slow rotators, and that for sufficiently high stellar angular velocities or sufficiently low mass accretion rates, the rotation of the star can be braked while accretion continues. These results are applied to pulsating X-ray sources, revealing that at high luminosities a star of given spin period rotating in the same direction as the disk can experience either spin-up or spin-down, depending on its luminosity. Also considered are the general problem of interpreting period changes in pulsating X-ray sources, and the dipole magnetic moments of nine pulsating X-ray sources are estimated by fitting the theoretical spin-up equation to estimates of the average luminosity and spin-up rate of each source.

Ghosh, P.↗
NASA NTRS1978

LANDSAT-2 and LANDSAT-3 Flight evaluation report

Flight performance analysis of LANDSAT 2 and LANDSAT 3 are presented for the period July 1978 to October 1978. Spacecraft operations and orbital parameters are summarized for each spacecraft. Data are provided on the performance and operation of the following subsystems onboard the spacecraft: power; attitude control; command/clock; telemetry; orbit adjust; magnetic moment compensating assembly; unified S band/premodulation processor; electrical interface; thermal narrowband tape recorders; wideband telemetry; attitude measurement sensor; wideband video tape recorders; return beam vidicon; multispectral scanner subsystem; and data collections.

Winchester, T. W.↗
NASA NTRS1982

Radio emission from Io

Radio observations of Io taken with the VLA at 2, 6, and 21 cm show flux densities of 11.6 + or - 0.2 mJy, and less than 0.5 mJy, respectively, where the latter is a 2 sigma upper limit. These flux densities correspond to Io disk brightness temperatures of T(b) (2 cm) = 98 + or - 17 K, T(b) (6 cm) = 85 + or - 16 K, and T(b) (21 cm) less than 400 K, respectively. These radio brightness temperatures are consistent with thermal emission expected from Io's surface on the basis of its infrared brightness temperature and its radio emissivity derived from radar studies. No evidence for nonthermal radio emission from Io is found, such as has been reported by Mingaliev et al (1979). By using a model for the generation of synchrotron emission at 21 cm by energetic electrons in a hypothetical Io magnetosphere, an upper limit of Io's dipole magnetic moment less than 2 x 10 to the 25th gauss/cu cm is found.

De Pater, I.↗
NASA NTRS1983

Solar wind flow about the terrestrial planets. II - Comparison with gas dynamic theory and implications for solar-planetary interactions

Bow shock models are employed to determine and compare the solar wind flows about Venus, Mars, and the earth. Initially, gas dynamic theory predictions are compared with the large data base available for the near-earth environment. The observed shape and location of the magnetopause proved sufficient for predicting the average dayside bow shock position to within 2% error. Use of the same gas dynamics theory produced highly disparate results for the flows past Venus and Mars. A variation of 510-1000 km altitude (high) for the solar wind-obstacle interface was found for Mars, thus requiring the presence of an effective magnetic moment of within 0.6 of 1.4 x 10 to the 22nd G/cu cm in the Martian magnetosphere, consistent with Viking data. The Venus bow wave was calculated to be closer to the planet than possible with a purely ionospheric interaction, indicating that solar wind-neutral atmosphere interactions in the lower ionosheath must necessarily be included in a gas dynamic modeling of the Venus obstacle to the solar wind.

Slavin, J. A.↗
NASA NTRS1983

On the equation of state of solar wind ions derived from Helios measurements

The radial evolution of such adiabatic invariants as the ion magnetic moments are studied on the basis of solar wind ion velocity distribution observations made by the Helios spacecraft between 0.3 and 1 AU. Significant differences between proton and alpha-particle parameters in wind velocity dependence are noted, and adiabaticity is on the average found to be violated. This violation is interpreted as evidence that protons are heated perpendicular to the field in fast streams. The contribution of the differential streaming energy to the total internal energy of the ions is also considered, and average heliocentric radial profiles for the ion heat fluxes are presented together with an examination of a possible ion heat flux role in the supply of thermal energy during the winds radial expansion. The present findings suggest that wave-particle interactions, and/or Coulomb collisions, are required to explain solar wind ion thermal energy states and radial temperature profiles.

Marsch, E.↗
NASA NTRS1983

On the origin of the 6.1-ms pulsar

A quantitative model is presented to account for the observed features of the binary pulsar PSR1953+53. A lower giant branch star is suggested to have evolved on a nuclear time scale while orbiting a neutron star, with mass transfer to the neutron star commencing when the giant attained its Roche lobe. A radius-core mass relationship was used to examined the processes that occurred after the hydrogen atmosphere was drained off to the neutron star. Tidal dissipation has circularized the orbit of the companion during mass transfer, while the orbit expanded. Accretion torques caused spin-up of the neutron star, which had a magnetic moment of no more than 3 x 10 to the 27th G/cu cm. The drained star became a degenerate dwarf with very faint luminosity, which accounts for no visual companion having been observed to date.

Joss, P. C.↗
NASA NTRS1983

Observational evidence on the origin of ions upstream of the earth's bow shock

The kinematic formalism described by Schwartz et al. (1983) is used to quantitatively compare the zeroth order predicted energies for four different source hypotheses for ions detected upstream of the earth's bow shock with previously published observations of upstream field-aligned beams and gyrating ion events. Specular reflection of a fraction of the incident solar wind is found to be the most credible explanation of gyrating ion events observed upstream of shocks ranging from quasi-parallel to nearly perpendicular. The recent hypothesis that field-aligned beams are the result of leakage from the magnetosheath of ions which were originally specularly reflected at quasi-perpendicular portions of the shock provides good agreement with observed energies of many field-aligned beams. Only magnetic moment conserving reflection of solar wind ions is capable of accounting for two very energetic beam events.

Thomsen, M. F.↗
NASA NTRS1983

Performance measurements of a pilot superconducting solenoid model core for a wind tunnel magnetic suspension and balance system

The results of experimental demonstrations of a superconducting solenoid model core in the Southampton University Magnetic Suspension and Balance System are detailed. Technology and techniques relevant to large-scale wind tunnel MSBSs comprise the long term goals. The magnetic moment of solenoids, difficulties peculiar to superconducting solenoid cores, lift force and pitching moment, dynamic lift calibration, and helium boil-off measurements are discussed.

Goodyer, M. J.↗
NASA NTRS1984

A radiometric Bode's Law: Predictions for Uranus

The magnetospheres of three planets, Earth, Jupiter, and Saturn, are known to be sources of intense, nonthermal radio bursts. The emissions from these sources undergo pronounced long term intensity fluctuations that are caused by the solar wind interaction with the magnetosphere of each planet. Determinations by spacecraft of the low frequency radio spectra and radiation beam geometry now permit a reliable assessment of the overall efficiency of the solar wind in stimulating these emissions. Earlier estimates of how magnetospheric radio output scales with the solar wind energy input must be revised greatly, with the result that, while the efficiency is much lower than previously thought, it is remarkably uniform from planet to planet. The formulation of a radiometric Bode's Law from which a planet's magnetic moment is estimated from its radio emission output is presented. Applying the radiometric scaling law to Uranus, the low-frequency radio power is likely to be measured by the Voyager 2 spacecraft as it approaches this planet.

Desch, M. D.↗
NASA NTRS1983

Electron velocity distributions near interplantary shocks

Previous work on electron heating mechanisms operating at the supercritical earth's bow shock is extended to the generally lower Mach number interplanetary shocks. This is done by studying electron velocity distributions observed both upstream and downstream of interplanetary shocks observed by ISEE 3 between August 1978 and December 1979. It is found that perpendicular heating accompanied by little or no parallel heating occurs at the weaker shocks but that parallel heating is dominant for the stronger shocks. When perpendicular heating is dominant, downstream velocity distributions are for the most part Gaussian at low energies (core) and Lorentzian at high energies (halo). When parallel heating is dominant, however, these distributions are flat-topped at low energies, having power law extensions to higher energies. At the weaker shocks, the observations are consistent with electron heating resulting from conservation of the magnetic moment, whereas at the stronger shocks the heating is quite similar to that observed at the earth's bow shock.

Feldman, W. C.↗
NASA NTRS1984

Progress towards large wind tunnel magnetic suspension and balance systems

Recent developments and current research efforts leading towards realization of a large scale production wind tunnel Magnetic Suspension and Balance facility are reviewed. Progress has been made in the areas of model roll control, high angle-of-attack testing, digital system control, high magnetic moment superconducting solenoid model cores, and system failure tolerance. Formal design studies of large scale facilities have commenced and are continuing.

Britcher, C. P.↗
NASA NTRS1984

Magnetospheric Structures: Uranus and Neptune

Magnetospheric structures that might be encountered at Uranus and Neptune are described. Statistics indicate a sufficiently high probability to warrant consideration of their likely properties in advance of the Voyager encounters. Because the spin axis of Uranus lies nearly in the ecliptic and presently points approximately sunward, Voyager is likely to encounter the unique pole on configuration that has special theoretical significance. Corotation in the magnetospheres of Uranus and Neptune would probably exclude solar wind drive convection as an important driver of global magnetospheric dynamics, as it does at Jupiter and Saturn. The magnetospheres of Uranus and Neptune probably lack sufficient internal sources of plasma to produce significant levels of rotationally driven convection. The reported observation of auroral emission from Uranus has therefore motivated the development of an alternative model in which solar wind motion is coupled directly to the rotation of the ionosphere to establish a dynamo circuit which generates Birkeland currents and polar cap aurora. This model predicts the strength and configuration of the aurora as functions of the magnitude and polarity, respectively, of the planetary magnetic moment.

T W Hill↗
NASA NTRS1985

Pulsars as cosmic ray accelerators: Energy development of protons

Results of numerical integrations of the Lorentz-Dirac-equation with Landau approximation for protons in the electromagnetic vacuum field of a magnetic dipole rotating with its angular velocity omega perpendicular to its magnetic moment mu will be discussed with special attention to the energy development of protons.

Thielheim, K. O.↗
NASA NTRS1985

Pulsars as cosmic ray particle accelerators: Dynamics of electrons

The Lorentz-Dirac-equation with Landau approximation has been solved numerically for electrons in the electromagnetic field of a magnetic dipole rotating with the angular velocity omega perpendicular to its magnetic moment mu. Results are discussed with respect to electron orbits and energy development.

Thielheim, K. O.↗
NASA NTRS1984

Magnetospheric energization by interaction between planetary spin and the solar wind

If the solar wind is capable of driving magnetospheric convection, then solar-wind flow past any spinning, magnetized planet with a conducting ionosphere must cause the magnetic field lines in the outer part of its magnetospheric tail to be twisted into a helix. Such a magnetic field configuration requires magnetically field-aligned (Birkeland) currents in the tail that flow in and near the magnetopause and close by driving Pedersen currents through the planetary ionosphere. The strength of the Birkeland currents (and, by current continuity, the Pedersen currents) is, to first order, independent of the angle between the planetary-spin vector and the solar-wind velocity vector. Rather, the total current is a function of the magnetic moment of the planet, the radius of the tail, the angular velocity of planetary spin, the conductivity of the ionosphere, and the solar wind speed. For Jupiter, Saturn, Uranus, and perhaps Neptune, the power these currents deliver to the ionosphere is significant with regard to magnetospheric dynamics, such as the production of aurora and the generation of low-frequency radio emissions. For Mercury, Venus, earth, Mars, and probably Pluto, these currents are relatively small, although observable effects may be marginally detectable for the case of the earth's magnetosphere.

Isbell, J.↗
NASA NTRS1985

Orientations of AM Her stars from their polarization properties - The case of the missing AM Her stars

Observation of the polarization properties of the AM Her stars is used to determine their orientations. It is found that the AM Her stars are randomly distributed with respect to their inclination angle i but not with respect to their magnetic colatitude delta. The stars are concentrated along the semicircle cos-squared delta + cos-squared i = 1, where delta is the angle between the magnetic moment and the spin axis of the degenerate dwarf. This result implies that the discovery of AM Her stars is strongly affected by observational selection effects. It is suggested that these effects are a result of the way in which the AM Her stars have been identified observationally, and of the angular properties of high harmonic cyclotron emission. It is estimated that there are about three times as many AM Her stars as have been found so far.

Brainerd, J. J.↗