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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Solar wind-plasma interaction: The AMPTE solar wind plasma releases

In situ measurements during AMPTE solar wind ion releases are described. The creation of a diamagnetic cavity, compression and draping of magnetic field lines, recoil of the entire artificial comet, and ion beam and tail formation are discussed. The wave measurements were used to determine the time variation of the plasma density from the measurement of the electron plasma frequency and to determine the state of cloud expansion and cavity formation. Features found include absence of strong turbulence and anomalous diffusion in the cavity boundary, and the appearance of very intense shock-like emission in front of the plasma clouds. The first effect suggests partially unknowm processes leading to magnetic field penetration into the region of the clouds. The direct observation of the interaction processes between the fast streaming solar wind plasma and the expanding cloud plasma of the Li and artificial comet releases may have relevance to astrophysical situations as, for instance, encountered in solar flares, interstellar clouds, or during accretion of matter onto compact objects.

Source record↗
NASA NTRS1987

Lageos orbit decay due to infrared radiation from earth

Infrared radiation from the earth may be the principal reason for the decay of Lageos' orbit. The radiation heats up the laser retroreflectors embedded in Lageos' aluminum surface. This creates a north-south temperature gradient on the satellite. The gradient in turn causes a force to be exerted on Lageos because of recoil from photons leaving its surface. The delayed heating of the retroreflectors due to their thermal inertia gives the force a net along-track component which always acts like drag. A simple thermal model for the retroreflectors indicates that this thermal drag accounts for about half the observed average along-track acceleration of -3.3 x 10 to the -10th power m/sec squared. The contribution from the aluminum surface to this effect is negligible. The infrared effect cannot explain the large observed fluctuations in drag which occur mainly when the orbit intersects the earth's shadow.

Rubincam, David Parry↗
NASA NTRS1988

Preliminary estimates of radiation exposures for manned interplanetary missions from anomalously large solar flare events

Preliminary estimates of radiation exposures for manned interplanetary missions resulting from anomalously large solar flare events are presented. The calculations use integral particle fluences for the February 1956, November 1960, and August 1972 events as inputs into the Langley Research Center nucleon transport code BRYNTRN. This deterministic code transports primary and secondary nucleons (protons and neutrons) through any number of layers of target material of arbitrary thickness and composition. Contributions from target nucleus fragmentation and recoil are also included. Estimates of 5 cm depth doses and dose equivalents in tissue are presented behind various thicknesses of aluminum, water, and composite aluminum/water shields for each of the three solar flare events.

Townsend, Lawrence W.↗
NASA NTRS1988

Analytical investigation of the dynamics of tethered constellations in earth orbit

This Quarterly Report on Tethering in Earth Orbit deals with three topics: (1) Investigation of the propagation of longitudinal and transverse waves along the upper tether. Specifically, the upper tether is modeled as three massive platforms connected by two perfectly elastic continua (tether segments). The tether attachment point to the station is assumed to vibrate both longitudinally and transversely at a given frequency. Longitudinal and transverse waves propagate along the tethers affecting the acceleration levels at the elevator and at the upper platform. The displacement and acceleration frequency-response functions at the elevator and at the upper platform are computed for both longitudinal and transverse waves. An analysis to optimize the damping time of the longitudinal dampers is also carried out in order to select optimal parameters. The analytical evaluation of the performance of tuned vs. detuned longitudinal dampers is also part of this analysis. (2) The use of the Shuttle primary Reaction Control System (RCS) thrusters for blowing away a recoiling broken tether is discussed. A microcomputer system was set up to support this operation. (3) Most of the effort in the tether plasma physics study was devoted to software development. A particle simulation code has been integrated into the Macintosh II computer system and will be utilized for studying the physics of hollow cathodes.

Lorenzini, Enrico C.↗
NASA NTRS1988

Cyclotron line resonant transfer through neutron star atmospheres

Monte Carlo methods are used to study in detail the resonant radiative transfer of cyclotron line photons with recoil through a purely scattering neutron star atmosphere for both the polarized and unpolarized cases. For each case, the number of scatters, the path length traveled, the escape frequency shift, the escape direction cosine, the emergent frequency spectra, and the angular distribution of escaping photons are investigated. In the polarized case, transfer is calculated using both the cold plasma e- and o-modes and the magnetic vacuum perpendicular and parallel modes.

Wang, John C. L.↗
NASA NTRS1989

Cyclotron line features from neutron star atmospheres

Cyclotron line features from the polar cap plasmas of accreting magnetized neutron stars are modeled. The polar cap environment is modeled by a homogeneous isothermal plane-parallel slab threaded by a uniform superstrong magnetic field oriented orthogonal to the slab. Two physical cyclotron photon source functions are used. For conventional stopping depths, the emergent line spectra are fairly independent of the source functions. For hot atmospheres the details of the line transfer using relativistic kinematics differ substantially from those using nonrelativistic kinematics. Aside from finite recoil, both a finite natural linewidth and conventional stopping depths suppress the escape of photons blueward of line center and potential line features tend to be smeared out into the low-energy continuum. The formation of a line features is most favorable in low-field high-temperature atmospheres where cyclotron photon production is confined to a layer of small column density.

Wang, John C. L.↗
NASA NTRS1988

Innovative uses of tethers in space

Potential uses of tethers in the fields of science, transportation, electrodynamics, and space exploration are discussed. Special attention is given to the use of tethers for scientific and planetary application, with descriptions of the type of measurements to be performed in a given science field or a planetary body and the particular method of tether use. Experiments proposed regarding the use of tethers will address some of the pending issues regarding the use of tethers, such as the tether deployment and control laws, the recoil, electrodynamic effects, the strength and survivability of tethers in the lower atmosphere, the stability of a tethered platform, and the propulsion through momentum exchange.

Ionasescu, Rodica↗
NASA NTRS1990

Comparison of dose estimates using the buildup-factor method and a Baryon transport code (BRYNTRN) with Monte Carlo results

Continuing efforts toward validating the buildup factor method and the BRYNTRN code, which use the deterministic approach in solving radiation transport problems and are the candidate engineering tools in space radiation shielding analyses, are presented. A simplified theory of proton buildup factors assuming no neutron coupling is derived to verify a previously chosen form for parameterizing the dose conversion factor that includes the secondary particle buildup effect. Estimates of dose in tissue made by the two deterministic approaches and the Monte Carlo method are intercompared for cases with various thicknesses of shields and various types of proton spectra. The results are found to be in reasonable agreement but with some overestimation by the buildup factor method when the effect of neutron production in the shield is significant. Future improvement to include neutron coupling in the buildup factor theory is suggested to alleviate this shortcoming. Impressive agreement for individual components of doses, such as those from the secondaries and heavy particle recoils, are obtained between BRYNTRN and Monte Carlo results.

Shinn, Judy L.↗
NASA NTRS1990

Images of the AMPTE artificial comets

Ground-based low-light-level CCD image observations were conducted of both Active Magnetospheric Particle Tracer Explorer artificial comet experiments. Preliminary image processing and gridding into absolute astronomical coordinates are presented to illustrate the dynamical features of the effects. In both cases, the neutral gas expanded at about 1.4 km/sec. The resultant plasma structures corresponding to the comet's head drifted perpendicularly to the direction of the solar wind at speeds of about 3 km/sec and about 1 km/sec, respectively. For the second comet, B(+) ejection speeds of about 10 km/sec preceded the recoil effect, and downstream accelerations of about 90 m/sec-squared were observed.

Mendillo, Michael↗
NASA NTRS1990

Further corrections to the theory of cosmological recombination

Krolik (1989) pointed out that frequency redistribution due to scattering is more important than cosmological expansion in determining the Ly-alpha frequency profile during cosmological recombination, and that its effects substantially modify the rate of recombination. Although the first statement is true, the second statement is not: a basic symmetry of photon scattering leads to identical cancellations which almost completely erase the effects of both coherent and incoherent scattering. Only a small correction due to atomic recoil alters the line profile from the prediction of pure cosmological expansion, so that the pace of cosmological recombination can be well approximated by ignoring Ly-alpha scattering.

Krolik, Julian H.↗
NASA NTRS1991

Intracloud development of lightning strikes to aircraft

The analysis of airborne electromagnetic records of seven lightning strikes to the FAA CV-580 instrumented airplane during the 1987 field campaign was aimed at revealing and interpreting processes taken place during the intracloud propagation of lighting strikes initiated on or intercepted by the airplane. It is shown that intracloud development of the strike may consist of recoil streamers, dart leader/return stroke sequences, and the secondary initiations of new discharges. These processes, with their high current pulse amplitudes, may present greater threat to aircraft than current pulses during strike initiation. The latter are presently considered by the technical community to be the primary lightning threat to aircraft.

Mazur, Vladislav↗
NASA NTRS1991

Bremsstrahlung and energetic electrons in supernovae

Explicit Monte Carlo calculations are presented for the rate of Compton scattering and for the spectrum recoil electrons per gram at discrete depths within models of supernovae, with emphasis on the bremsstrahlung emissivity within supernova interiors. The spectrum of the bremsstrahlung emissivity is calculated at E to the -1.3 for a wide range of supernova models. The radial and temporal dependence of that emissivity is calculated for two models of SN 1987A and for one model of a Type Ia and of a He core explosion model of a Type Ib. The spectrum emerging from the surface, which is then evaluated by Monte Carlo techniques, was found to be sensitive to the photoelectric opacity and inverted by it, i.e., the spectral luminosity of the bremsstrahlung component increases slowly between 1 and 30 keV even though the emissivity declines with energy within that energy band. The bremsstrahlung luminosity was found to dominate that of the primary scattered gammas for E of less than 20 keV.

Clayton, Donald D.↗
NASA NTRS1990

Astrogam - A magnetic rigidity spectrometer for gamma-ray astronomy

A novel concept is presented for a high-energy gamma-ray telescope with an extended energy range and excellent energy and angular resolution. The characteristics of Astrogam, a wide-field camera which makes an all-sky survey, are enumerated. Consideration is given to the instrument's unique features: wide energy range (four orders of magnitude and energy, which will bridge the gap between satellite and ground-based observations); excellent source location precision (multiple scattering error dominating nuclear recoil and measurement error below 20 GeV); and excellent energy resolution (1-percent energy resolution). Astrogam will make observations in the GTE energy range possible and could resolve complex source regions like the Crab pulsar/Nebular system, the Galactic center, and the Geminga region as well as discover the true nature of the sources.

Adams, James H., Jr.↗
NASA NTRS1992

Light-heavy ion measurements in CR-39 located on the Earth side of LDEF

The azimuthal angle distribution and the charge and energy spectra of selected light-heavy (3 less than or = Z less than or = 8) stopping particles were measured in a single layer of CR-39 plastic nuclear track detector (PNTD) from the stack of the A0015 experiment located on the Earth-end of the satellite. The directional incidence of the trapped protons is studied by comparing the azimuthal angle distribution of selected recoils, obtained in the LDEF detectors, to that obtained through calibrations of PNTDs with exposure performed with 200 MeV proton beams from different directions. Similar measurements will be performed in a CR-39 sample exposed on the space-end of the LDEF satellite for intercomparison. The experimental results will also be compared to theoretical calculations.

Csige, I.↗
NASA NTRS1992

Charge Dependence and Electric Quadrupole Effects on Single-Nucleon Removal in Relativistic and Intermediate Energy Nuclear Collisions

Single nucleon removal in relativistic and intermediate energy nucleus-nucleus collisions is studied using a generalization of Weizsacker-Williams theory that treats each electromagnetic multipole separately. Calculations are presented for electric dipole and quadrupole excitations and incorporate a realistic minimum impact parameter, Coulomb recoil corrections, and the uncertainties in the input photonuclear data. Discrepancies are discussed. The maximum quadrupole effect to be observed in future experiments is estimated and also an analysis of the charge dependence of the electromagnetic cross sections down to energies as low as 100 MeV/nucleon is made.

Norbury, John W.↗
NASA NTRS1992

Measurements of LET spectra and comparison to models

Measurements of LET spectra for near-earth orbits with various inclinations and altitudes are presented. A comparison with calculated LET spectra shows that the contribution from direct ionizing galactic cosmic rays is well described by the models. An additional contribution to the spectra originates from stopping protons and from nuclear interactions of particles with material. In the case of an interaction, a large amount of energy is deposited in a small volume by target recoils or target fragments. These events will be called short range (SR) events. For a low-inclination orbit radiation belt protons are the main source of these events while galactic protons become more important when increasing the inclination to near-polar orbits. It is shown that the contribution of SR events for orbits with low altitude (324 km) and 57-deg inclination is comparable to that for an orbit with 28-deg inclination at a high altitude (510 km).

Wiegel, B.↗
NASA NTRS1991

Solar flare gamma-ray line profiles

Solar gamma-ray lines are produced through collisions of pairs of positive ions whose center of mass energies are above the relevant thresholds for excitation of gamma-ray emitting states. Because of the low density of the solar plasma, prompt gamma rays are emitted by recoiling ions before significant energy loss has occurred. Thus, the lines are expected to be Doppler-broadened to widths of the order of a hundred KeV. Gamma-ray lines resulting from proton and alpha-particle (He-4 ion) beams on carbon and oxygen targets in the laboratory exhibit complex profiles which change rapidly with the gamma-ray observation angle. Earlier work has been limited to modeling laboratory and solar flare gamma-ray profiles produced by proton excitation, but laboratory profiles of the carbon 4.44-MeV line and oxygen 6.13-MeV line from alpha excitation have now been successfully modeled. Solar flare gamma-ray line profiles of the carbon and oxygen lines from heavy ions in the ambient solar medium interacting with representative high-energy proton and alpha particle populations are presented.

Lang, F. L.↗