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At least 991 records · Page 55
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NASA NTRS1986

Space solar cell research - Problems and potential

The value of a passive, maintenance-free, renewable energy source was immediately recognized in the early days of the space program, and the silicon solar cell, despite its infancy, was quickly pressed into service. Efficiencies of those early space solar arrays were low, and lifetimes shorter than hoped for, but within a decade significant advances had been made in both areas. Better performance was achieved because of a variety of factors, ranging from improvements in silicon single crystal material, to better device designs, to a better understanding of the factors that affect the performance of a solar cell in space. Chief among the latter, particularly for the mid-to-high altitude (HEO) and geosynchronous (GEO) orbits, are the effects of the naturally occurring particulate radiation environment. Although not as broadly important to the photovoltaic community at large as increased efficiency, the topic of radiation damage is critically important to use of solar cells in space, and is a major component of the NASA research program in space photovoltaics. This paper will give a brief overview of some of the opportunities and challenges for space photovoltaic applications, and will discuss some of the current reseach directed at achieving high efficiency and controlling the effects of radiation damage in space solar cells.

Flood, Dennis J.↗
NASA NTRS1987

Satellite observations of new particle and field signatures associated with SAR arc field lines at magnetospheric heights

Enhancements in thermal ion densities, an oxygen dominated ring current at energies below 17 keV, and invariant latitude-limited bands of intense ELF hiss have been discovered on Stable Auroral Red (SAR) arc field lines at magnetospheric heights. These new signatures were revealed by an examination of 31 coordinated data sets taken simultaneously at magnetospheric and ionospheric heights by the De-1 and -2 satellites during SAR arc traversals within the period September 1981 through April 1982. Data sets from DE-2, for the first time, provide information on the location of a SAR arc (determined by the F region electron temperature enhancement) during the nearly simultaneous passage of these field lines by DE-1 in the magnetosphere. These new high altitude signatures are examined in the context of possible magnetospheric SAR arc energy source mechanisms.

Kozyra, J. U.↗
NASA NTRS1987

Distortion of the cosmic background radiation by superconducting strings

Superconducting cosmic strings can be significant energy sources, keeping the universe ionized past the commonly assumed epoch of recombination. As a result, the spectrum of the cosmic background radiation is distorted in the presence of heated primordial gas via the Suniaev-Zel'dovich effect. Thiis distortion can be relatively large: the Compton y parameter attains a maximum in the range 0.001-0.005, with these values depending on the mass scale of the string. A significant contribution to y comes from loops decaying at high redshift when the universe is optically thick to Thomson scattering. Moreover, the isotropic spectral distortion is large compared to fluctuations at all angular scales.

Ostriker, J. P.↗
NASA NTRS1988

Line variability and the broad emission line region of quasi-stellar objects. II - Changes in Balmer decrements

Evidence is presented for significant variations of broad emission lines in five QSOs supporting an earlier report by Zheng et al. (1987). The Balmer decrements before and after variations are compared in an effort to extract information on the broad-line regions. The broad hydrogen lines are found to vary in step with the underlying continuum, indicating that the continuum is the probable energy source for emission lines. The ratios of H-beta/H-alpha for both the varying and steady parts of the the broad lines are about 0.2, suggesting that the regions in which these line fluxes originate are exposed to similar ionizing flux and are therefore at about the same distance to the central source. The average ratio of H-gamma/H-beta is 0.8 for the variable components, considerably higher than that of the constant components. Thus, the region producing the varying line fluxes may have higher density and lower optical depth.

Zheng, Wei↗
NASA NTRS1987

Vertical temperature gradients on Uranus - Implications for layered convection

Analyses of Voyager IR spectroscopy and radio occultation measurements confirm ground-based observations that the deep lapse rate of Uranus exceeds that for an adiabat of H2 in thermodynamic equilibrium. However, in approximately the same region of the atmosphere, Voyager IR and ground-based observations also indicate that the ratio of ortho to para hydrogen is near the equilibrium value. These two sets of observations can be reconciled by postulating the existence of rapid convective overturning within layers which are thin in comparison to a pressure scale height. Two forms of layered convection are examined. In one case, deposition of kinetic energy results in thin, rapidly overturning layers. Possible kinetic energy sources include braking waves and local instabilities. In the second case considered, molecular-weight discontinuities due to CH4 stratification stabilize the interfaces of thin layers. It is argued that both forms may be important in the convective portion of the Uranus atmosphere.

Gierasch, Peter J.↗
NASA NTRS1988

X-rays from supernova 1987A

Detailed calculations of the development of the X-ray spectrum of 1987A are presented using more realistic models for the supernova composition and density structure provided by Woosley. It is shown how the emergence of the X-ray spectrum depends on the parameters of the model and the nature of its central energy source. It is shown that the soft X-ray spectrum should be dominated by a 6.4 keV Fe K(alpha) emission line that could be observed by a sensitive X-ray telescope.

Xu, Yueming↗
NASA NTRS1988

H2 and H I emission line imaging of the ring nebula (NGC 6720)

Infrared emission-line images of the v = 1-0 S(1) transition of molecular hydrogen and Br-gamma recombination line of atomic hydrogen which cover the entire extent of NGC 6720, the Ring nebula. The maps presented here are the highest angular resolution images of these transitions yet produced for this object and have very low relative positional uncertainty. As a result, the spatial stratification of the ionized and shocked molecular zones within the nebula is clearly resolved. These data, and data from the Infrared Astronomical Satellite, are used to determine the H2, H I, and dust mass within the nebula. Energy sources for the dust heating, formation and destruction of the H2, and overall evolution of the nebula are also discussed.

Greenhouse, Matthew A.↗
NASA NTRS1988

Theoretical infrared spectra of SN 1987A

A simple model for the ejecta of SN 1987A is used to show that the expected fluxes in infared fine structure lines from nickel, cobalt, iron, argon, sulfur, silicon, and neon are likely to be detectable for several years following the supernova explosion. Energy sources due to radioactive decay and a central pulsar are considered separately. Most of the mass of heavy elements resides in the inner, pure metal shells of the ejecta, so that the infrared lines will probe the temperature, ejecta masses, and dynamics of this region and not the overlying, hydrogen-rich envelope.

Colgan, Sean W. J.↗
NASA NTRS1988

The stellar wind velocity function for red supergiants determined in eclipsing binaries

The potential for direct measurement of the acceleration of stellar winds from the supergiant component of Zeta Aurigae-type binary stars is discussed. The aberration angle of the interaction shock cone centered on the hot star provides a measure of the velocity of the cool star wind at the orbit of the secondary. This is confirmed by direct observations of stellar wind (P Cygni) line profile variations. This velocity is generally smaller than the final (terminal) velocity of the wind, deduced from the P Cygni line profiles. The contrast between these results and previously published supergiant wind models is discussed. The implication on the physics of energy source dissipation predicted in the theoretical models is considered.

Ahmad, Imad A.↗
NASA NTRS1988

Evolution of planetesimal velocities

The velocity evolution of a general planetesimal population is treated by means of a self-consistent set of equations whose form is tailored to those early planetary accumulation stages in which the planetesimal swarm's modeling calls for gas dynamic methods. Dynamical friction is noted to be essential to the transfer of kinetic energy from larger to smaller planetesimals, thereby furnishing an energy source comparable to those furnished by viscous stirring.

Stewart, Glen R.↗
NASA NTRS1988

Small-aperture infrared photometry of Seyfert 1 galactic nuclei

Multiaperture infrared photometry of the nuclei of five Seyfert 1 galaxies is presented. When apertures approaching the seeing limit were used, it was found that all of the nuclei have observed power law energy distributions with F(nu) proportional to 1/nu sq from 1.25 to 3.45 micron. After correcting for reddening, the spectral indices had a range of alpha = 1.4-1.9. These results are supported through infrared imaging of one of the program galaxies, and they demonstrate the importance of properly isolating the nuclear component from the stellar disk through the use of extremely small apertures. Although the nature of the infrared emissions cannot be determined, results indicate that a common energy source exists among the observed galaxies.

Simons, D. A.↗
NASA NTRS1988

Europa - The prospects for an ocean

Tidal dissipation in the satellites of a giant planet may provide sufficient heating to maintain a liquid water ocean below a thin ice layer. In the solar system, Europa, one of the Galilean satellites of Jupiter, may have such an ocean. Both theoretical calculations and certain observations support its existence, although proof is lacking. The putative ocean would probably have temperatures, pressures, and chemistry conducive to biologic activity. However, the environment would be severely energy limited. Possible energy sources include transient transmission of sunlight through fractures in the ice and hydrothermal activity on the ocean floor. While temporary conditions could exist that are within the range of adaptation of certain terrestrial organisms, origin of life under such conditions seems unlikely. In other solar systems, however, larger satellites with more significant heat flow could provide environments that are stable over an order of aeons and in which life could perhaps evolve.

Reynolds, R. T.↗
NASA NTRS1989

Free-Piston Stirling Engines

Engines promise cost-effective solar-power generation. Report describes two concepts for Stirling-engine systems for conversion of solar heat to electrical energy. Recognized most promising technologies for meeting U.S. Department of Energy goals for performance and cost for terrestrial electrical-energy sources.

Shaltens, Richard K.↗
NASA NTRS1988

Continuing the biological exploration of Mars

Mars has been an object of interest for the better part of this century. To a biologist, Mars assumes special importance because many aspects of the theory of chemical evolution for the origin of life can be tested there. The central idea of this theory is that life on a suitable planet arises through a process in which the so-called biogenic elements combine to form increasingly more complex molecules under the influence of naturally-occurring energy sources ultimately resulting in the formation of replicating organic molecules. The biogenic elements are present on Mars today. Furthermore, the available evidence also strongly suggests that Mars may have had an early history similar to that of the Earth, including a period in which large amounts of liquid water once flowed on its surface and a denser atmosphere and higher global temperatures prevailed. This is important since many lines of evidence indicate that living organisms were already present on the Earth within the first billion years after its formation at a time when the environment on Mars may have closely resembled that of Earth. Our current knowledge of the state of chemical evolution on Mars can best be described as paradoxical. Most of what we have learned has come from experiments performed on the Viking landers. The combination of planned investigations covered a broad range of techniques to detect signs of chemical evolution. The most surprising data from all of these was the absence of any detectable quantities of organic compounds at the two landing sites. On the other hand, the Viking experiments did indicate that the Martian surface samples contained unidentified strong oxidant(s) that could account for their absence.

Klein, Harold P.↗
NASA NTRS1988

New Herbig-Haro objects in star-forming regions

A list of 25 new Herbig-Haro objects, HH 58 to HH 82, in the Orion molecular clouds and in southern molecular cloud complexes has been compiled. CCD images in the S II 6717, 6731 forbidden lines are presented for the objects, together with a few spectra and some IR observations. The individual objects and, when identified, their energy sources are discussed. HH 65 is located in the red lobe of the bipolar outflow associated with the highly variable reflection nebula Re 50. HH 67 is a 22-arcsec long sinusoidal jet. HH 68/69 consists of a long, linear chain of four HH knots. HH 72 emerges from a 120-solar luminosity IRAS source embedded in a Bok globule. HH 79 is the first HH object discovered in the Ophiuchus clouds. HH 80/81 in Sagittarius are among the brightest HH objects known, have complex velocities, high excitation conditions and emerge from a 6000-solar luminosity young B-star. HH 82 is associated with the bright variable star S Coronae Australis.

Reipurth, BO↗
NASA NTRS1988

Hydrogen and helium excitation by EUV radiation for the production of white-light flares

Non-LTE radiative transfer calculations for hydrogen and helium in a simple model atmosphere are used to demonstrate that EUV radiation cannot be the main energy source for white-light flares. The opacities in the Lyman continuum and the helium I and II continua are found to be much larger than the enhanced opacity in the visible hydrogen continuum. It is shown that the EUV radiation is absorbed before it can have a significant effect on the visible light continuum.

Poland, A. I.↗
NASA NTRS1988

Density and white light brightness in looplike coronal mass ejections - Temporal evolution

Three ambient coronal models suitable for studies of time-dependent phenomena were used to investigate the propagation of coronal mass ejections initiated in each atmosphere by an identical energy source. These models included those of a static corona with a dipole magnetic field, developed by Dryer et al. (1979); a steady polytropic corona with an equatorial coronal streamer, developed by Steinolfson et al. (1982); and Steinolfson's (1988) model of heated corona with an equatorial coronal streamer. The results indicated that the first model does not adequately represent the general characteristics of observed looplike mass ejections, and the second model simulated only some of the observed features. Only the third model, which included a heating term and a streamer, was found to yield accurate simulation of the mess ejection observations.

Steinolfson, R. S.↗
NASA NTRS1989

Disturbances along the Arizona monsoon boundary

The possibility of the occurrence of disturbances along the 'Arizona monsoon boundary' (the boundary between two air masses in the southwestern U.S. and northwestern Mexico) during the summer is evaluated. Linear calculations demonstrate that the monsoon boundary is indeed unstable, with maximum growth rates of 0.4-0.6/d at a wavelength near 1200 km. It is found that the energy source for the most unstable waves is baroclinic and that the waves are barotropically damped.

Moore, Thomas J.↗