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NASA NTRS2007

Observational Evidence of a Hemispheric-wide Ice-ocean Albedo Feedback Effect on Antarctic Sea-ice Decay

The effect of ice-ocean albedo feedback (a kind of ice-albedo feedback) on sea-ice decay is demonstrated over the Antarctic sea-ice zone from an analysis of satellite-derived hemispheric sea ice concentration and European Centre for Medium-Range Weather Forecasts (ERA-40) atmospheric data for the period 1979-2001. Sea ice concentration in December (time of most active melt) correlates better with the meridional component of the wind-forced ice drift (MID) in November (beginning of the melt season) than the MID in December. This 1 month lagged correlation is observed in most of the Antarctic sea-ice covered ocean. Daily time series of ice , concentration show that the ice concentration anomaly increases toward the time of maximum sea-ice melt. These findings can be explained by the following positive feedback effect: once ice concentration decreases (increases) at the beginning of the melt season, solar heating of the upper ocean through the increased (decreased) open water fraction is enhanced (reduced), leading to (suppressing) a further decrease in ice concentration by the oceanic heat. Results obtained fi-om a simple ice-ocean coupled model also support our interpretation of the observational results. This positive feedback mechanism explains in part the large interannual variability of the sea-ice cover in summer.

Nihashi, Sohey↗

NASA NTRS1994

Diffused ionized gas in the spiral galaxy M31

We present a study of diffuse ionized gas (DIG, or WIM for warm ionized medium) in the nearby spiral M31, based on charge coupled device (CCD) imagery in H alpha and (S II) emission lines. We find that the DIG in M31 contributes 40% of the observed total H alpha luminosity, and at least 20% of the total after correction for extinction. This fraction is constant across the disk of M31. The total H alpha luminosity of M31, corrected for extinction, is about 4.1 x 10(exp 40) ergs/s. This implies a low star formation rate of about 0.35 M solar mass/yr, in agreement with earlier estimates. DIG is concentrated near regions of star formation. The average emission measure (EM) perpendicular to the disk ranges from about 6 pc cm(exp-6) in weaker spiral arms to 15 pc cm(exp-6) in the main spiral arms, with (rare) peak values reaching 50 pc cm(exp-6). Overall, the EM in the main arms is substantially higher than that of DIG in the solar neighborhood, implying higher power requirements per unit area in these regions of M31. However, the strong concentration of DIG near regions of star formation keeps the total area covered by DIG in M31 relatively small, which makes it possible to sustain this gas in spite of the low star formation rate. We argue that the DIG extent in vertical direction in M31 may well be lower than in our Galaxy, because of its low star formation rate. A simple parameterization of the electron distribution then shows that the DIG in the spiral arms may contribute between 15% and 40% of the total atomic gas column. The average electron densities implied by the high EMs reached in some regions seem to indicate a higher thermal pressure in the DIG than in the diffuse H I gas in M31. This pressure in-equilibrium can be avoided if part of the diffuse emissions due to a denser component, as proposed most recently by Miller & Cox, because this would reduce the EM and implied pressures for the actual widespread DIG. Column densities of the ionized gas might then be lower as well. We also show, however, that it is not possible to attribute all of the diffuse emission to a relatively dense component, such as earlier proposed extended low-density H II regions. The DIG in M31 shows an overall (S II)/H alpha intensity ratio of 0.5, significantly higher than in discrete H II regions, and similar to that in other galaxies. This number does not vary with radius in M31. There is a suggestion that (S II)/H alpha intensity may be higher at the lowest detectable emission measures, up to 0.7 or even 1. The discrete source population in M31 also shows a trend toward increasing (S II)/H alpha flux ratios as the sources become more diffuse. Few sources (apart from supernova remnants), however, reach the value of 0.5 found in the DIG as a whole. The distinct spectral signature of the DIG in M31, and its energy requirements favor photoionization of the gas, although it is likely that shock ionization occurs in selected regions.

Walterbos, Rene A. M.↗

NASA NTRS1980

Generalized shading analysis for paraboloidal collector fields

This paper presents the development and results of a generalized shading analysis for a field of point-focus parabolic dish concentrators. Shading of one concentrator by another with attendant loss of energy is a function of the position of the sun and the relative locations of the concentrators within the field. A method is presented for determining the annualized energy loss which includes a trade-off of system life-cycle energy as a function of concentrator spacing and field geometric layout. System energy output is computed on an annualized basis, employing 15 minute-increment environmental data tapes for the year 1976 at Barstow, California. For a land cost of $5000 per acre, lowest system energy cost occurs at about a 25 percent packing fraction (concentrator area/land area) for a typical 1-MWe dish-Stirling solar thermal power plant. Basic equations are given for computing the shading and concomitant energy loss as a function of concentrator center-to-center spacing, field layout site location.

Osborn, D. B.↗

NASA NTRS1985

Vacuum MOCVD fabrication of high efficience cells

Vacuum metal-organic-chemical-vapor-deposition (MOCVD) is a new fabrication process with improved safety and easier scalability due to its metal rather than glass construction and its uniform multiport gas injection system. It uses source materials more efficiently than other methods because the vacuum molecular flow conditions allow the high sticking coefficient reactants to reach the substrates as undeflected molecular beams and the hot chamber walls cause the low sticking coefficient reactants to bounce off the walls and interact with the substrates many times. This high source utilization reduces the materials costs power device and substantially decreases the amounts of toxic materials that must be handled as process effluents. The molecular beams allow precise growth control. With improved source purifications, vacuum MOCVD has provided p GaAs layers with 10-micron minority carrier diffusion lengths and GaAs and GaAsSb solar cells with 20% AMO efficiencies at 59X and 99X sunlight concentration ratios. Mechanical stacking has been identified as the quickest, most direct and logical path to stacked multiple-junction solar cells that perform better than the best single-junction devices. The mechanical stack is configured for immediate use in solar arrays and allows interconnections that improve the system end-of-life performance in space.

Partain, L. D.↗

NASA NTRS1977

Solar heating and cooling technical data and systems analysis

The research activities described herein were concentrated on the areas of economics, heating and cooling systems, architectural design, materials characteristics, climatic conditions, educational information packages, and evaluation of solar energy systems and components.

Christensen, D. L.↗

NASA NTRS1980

Time-average fluxes of heavy ions at the geostationary orbit

Measurements of average proton, helium, carbon, and oxygen fluxes at 6.6 earth radii are reported. The data represent averages obtained on ATS 6 between June 15 and Oct. 3, 1974. The energy range covered was 0.36-1.1 MeV for protons and approximately 1-4 MeV for the heavier ions. The results indicate that above about 1 MeV the heavier ion fluxes dominate over the proton flux on the energy/ion scale. Using two different spectral dependencies to fit the data, the carbon to oxygen concentration ratio for energies above 1 MeV was found to be 0.43 for the power law spectrum and 0.44 for the exponential spectrum. Thus in either case the abundance ratio is consistent with the solar origin of the particles. Similarly, the helium to oxygen concentration ratio is found to be 0.17 for the power law spectrum and 0.28 for the exponential spectrum. This is inconsistent with the solar wind ratio, which is about 10. The results quoted above are based on a very small portion of the distribution function above 1 MeV.

Konradi, A.↗

NASA NTRS1972

Synthesis of data obtained at Jicamarca, Peru, during the September 11, 1969, eclipse.

Results of continuous measurements of electron temperatures, electron concentrations, and vertical plasma drift made at Jicamarca during the Sept. 11, 1969, solar eclipse and of control measurements made on Sept. 13, 1969. Synthesis of the observed electron concentrations was made, using a model that solved the time-dependent electron-ion continuity equations. Ions O(-), NO(+), O2(+), and N2(+) were treated. Physical and chemical processes pertinent to the F region were considered in a realistic way. At noon, 300 km above Jicamarca, the values q = 290 per cu cm per sec for the O(+) production rate, beta = 1.94 x 0.0001 per sec for the loss coefficient, and H = 59 km for the atomic oxygen scale height were obtained. All large-scale features observed in the F2 region were synthesized by the model. This synthesis was not sensitive to a simultaneous 30% reduction of q and beta.

Sterling, D. L.↗

NASA NTRS1984

Uncertainties about the physical electronics of n(+) and p(+) silicon, with applications for solar cells

After brief surveys of the significance of n(+) and p(+) silicon for the conversion efficiency of solar cells, the work in this paper is concentrated on uncertainties in the characterization of n(+) and p(+) regions. The topics treated include the quantum density states of the majority carrier band and the position of the Fermi level relative to the edge of this band, the resulting force field on the minority carriers accompanying a space dependence of the energy gap narrowing, and the interpretation of measurements of the energy gap narrowing and the minority carrier diffusivity and mobility. The treatment seeks to show how these uncertainties relate to solar cell design and to estimates of attainable conversion efficiency.

Lindholm, F. A.↗

NASA NTRS1986

Potential high efficiency solar cells: Applications from space photovoltaic research

NASA involvement in photovoltaic energy conversion research development and applications spans over two decades of continuous progress. Solar cell research and development programs conducted by the Lewis Research Center's Photovoltaic Branch have produced a sound technology base not only for the space program, but for terrestrial applications as well. The fundamental goals which have guided the NASA photovoltaic program are to improve the efficiency and lifetime, and to reduce the mass and cost of photovoltaic energy conversion devices and arrays for use in space. The major efforts in the current Lewis program are on high efficiency, single crystal GaAs planar and concentrator cells, radiation hard InP cells, and superlattice solar cells. A brief historical perspective of accomplishments in high efficiency space solar cells will be given, and current work in all of the above categories will be described. The applicability of space cell research and technology to terrestrial photovoltaics will be discussed.

Flood, D. J.↗

NASA NTRS1995

The Astro Edge solar array for the NASA SSTI Clark Spacecraft

The Astro Edge solar array is a new and innovative reflective low concentrator power generating system which has been selected for the CTA Incorporate/Lockheed Martin Clark spacecraft under the NASA Small Spacecraft Technology Initiative (SSTI) program. In support of this program, Astro Aerospace Corporation has produced one qualification and two flight solar array wings to support a July 1996 launch. The Astro Edge solar array was selected as a new technology to benefit future NASA, military and commercial missions by providing high specific power, high deployed stiffness, low stowed volume, low risk, and cost reduction features which meet the agency's 'better, faster, cheaper' goals. This novel array accounts for five of the thirty-six advanced technologies which the Clark spacecraft will demonstrate. A brief SSTI Astro Edge solar array program overview is presented. Completed qualification and acceptance testing is discussed. Finally, the major discriminators which make the Astro Edge solar array 'better, faster, cheaper' technology are provided.

Spence, B. R.↗

NASA NTRS2007

Recovery of Electron/Proton Radiation-Induced Defects in n+p AlInGaP Solar Cell by Minority-Carrier Injection Annealing

A high efficient In0.48Ga0.52P/In0.01Ga0.99As/Ge triple junction solar cell has been developed for application in space and terrestrial concentrator PV system [1-3]. Recently, a high conversion efficiency of 31.5% (AM1.5G) has been obtained in InGaP/(In)GaAs/Ge triple junction solar cell, and as a new top cell material of triple junction cells, (Al)InGaP [1] has been proposed to improve the open-circuit voltage (Voc) because it shows a higher Voc of 1.5V while maintaining the same short-circuit current (ISC) as a conventional InGaP top cell under AM1.5G conditions as seen in figure 1 (a). Moreover, the spectral response of 1.96eV AlInGaP cell with a thickness of 2.5..m shows a higher response in the long wavelength region, compared with that of 1.87eV InGaP cell with 0.6..m thickness, as shown in figure 1 (b). Its development will realize next generation multijunction (MJ) solar cells such as a lattice mismatched AlInGaP/InGaAs/Ge 3-junction and lattice matched AlInGaP/GaAs/InGaAsN/Ge 4-junction solar cells. Figure 2 shows the super high-efficiency MJ solar cell structures and wide band spectral response by MJ solar cells under AM1.5G conditions. For realizing high efficient MJ space solar cells, the higher radiation-resistance under the electron or proton irradiation is required. The irradiation studies for a conventional top cell InGaP have been widely done [4-6], but little irradiation work has been performed on AlInGaP solar cells. Recently, we made the first reports of 1 MeV electron or 30 keV proton irradiation effects on AlInGaP solar cells, and evaluated the defects generated by the irradiation [7,8]. The present study describes the recovery of 1 MeV electron / 30 keV proton irradiation-induced defects in n+p- AlInGaP solar cells by minority-carrier injection enhanced annealing or isochronal annealing. The origins of irradiation-induced defects observed by deep level transient spectroscopy (DLTS) measurements are discussed.

Lee, H. S.↗

NASA NTRS1996

Impact of Chromophoric Dissolved Organic Matter on UV Inhibition of Primary Productivity in the Sea

A model was developed to assess the impact of chromophoric dissolved organic matter (CDOM) on phytoplankton production within the euphotic zone. The rate of depth-integrated daily gross primary productivity within the euphotic zone was evaluated as a function of date, latitude, CDONI absorption characteristics, chlorophyll a (chl a) concentration, vertical stratification, and phytoplankton sensitivity to UV radiation (UVR). Results demonstrated that primary production was enhanced in the upper 30 m of the water column by the presence of CDOM, where predicted increases in production due to the removal of damaging UVR more than offset its reduction resulting from the absorption of photosynthetically usable radiation. At greater depths, where little UVR remained, primary production was always reduced due to removal by CDOM of photosynthetically usable radiation. When CDOM was distributed homogeneously within the euphotic zone, the integral over z [(GPP)(sub ez)], was reduced under most bio-optical (i.e. solar zenith angle, and CDOM absorption, and ozone concentration) and photophysiological production at depth was greater than the enhancement of production at the surface.

Arrigo, Kevin R.↗

NASA NTRS1985

Overview of SERI's high efficiency solar cell research

The bulk of the research efforts supported by the Solar Energy Research Institute (SERI) High Efficiency Concepts area has been directed towards establishing the feasibility of achieving very high efficiencies, 30% for concentrator and more than 20% for thin film flat plate, in solar cell designs which could possibly be produced competitively. The research has accomplished a great deal during the past two years. Even though the desired performance levels have not yet been demonstrated, based on the recent progress, a greater portion of the terrestrial photovoltaics community believes that these efficiencies are attainable. The program will now allocate a larger portion of resources to low cost, large area deposition technology. The program is currently shifting greater emphasis on to the study of crystal growth in order to provide the understanding and tools needed to design a large area process.

Benner, J. P.↗

NASA NTRS2004

Toward Effective Shell Modeling of Wrinkled Thin-Film Membranes Exhibiting Stress Concentrations

Geometrically nonlinear shell finite element analysis has recently been applied to solar-sail membrane problems in order to model the out-of-plane deformations due to structural wrinkling. Whereas certain problems lend themselves to achieving converged nonlinear solutions that compare favorably with experimental observations, solutions to tensioned membranes exhibiting high stress concentrations have been difficult to obtain even with the best nonlinear finite element codes and advanced shell element technology. In this paper, two numerical studies are presented that pave the way to improving the modeling of this class of nonlinear problems. The studies address the issues of mesh refinement and stress-concentration alleviation, and the effects of these modeling strategies on the ability to attain converged nonlinear deformations due to wrinkling. The numerical studies demonstrate that excessive mesh refinement in the regions of stress concentration may be disadvantageous to achieving wrinkled equilibrium states, causing the nonlinear solution to lock in the membrane response mode, while totally discarding the very low-energy bending response that is necessary to cause wrinkling deformation patterns. An element-level, strain-energy density criterion is suggested for facilitating automated, adaptive mesh refinements specifically aimed at the modeling of thin-film membranes undergoing wrinkling deformations.

Tessler, Alexander↗

NASA NTRS2006

Geometrically Nonlinear Shell Analysis of Wrinkled Thin-Film Membranes with Stress Concentrations

Tessler, Alexander↗

NASA NTRS1978

Cost analysis of new and retrofit hot-air type solar assisted heating systems

A detailed cost analysis/cost improvement study was performed on two Department of Energy/National Aeronautics and Space Administration operational test sites to determine actual costs and potential cost improvements of new and retrofit hot air type, solar assisted heating and hot water systems for single family sized structures. This analysis concentrated on the first cost of a system which included procurement, installation, and integration of a solar assisted heating and hot water system on a new or retrofit basis; it also provided several cost projections which can be used as inputs to payback analyses, depending upon the degree of optimism or future improvements assumed. Cost definitions were developed for five categories of cost, and preliminary estimates were developed for each. The costing methodology, approach, and results together with several candidate low cost designs are described.

Stewart, R. D.↗

NASA NTRS1989

Climatology of nitric oxide in the upper stratosphere, mesosphere, and thermosphere - 1979 through 1986

The contents of NO in the upper stratosphere, mesosphere, and thermosphere were determined as a function of time and latitude, using spectral scan data for 1979 through 1986 from the solar backscattered UV instrument on Nimbus 7. In that period, the integrated column amount of NO near the equator decreased from 6.4 x 10 to the 14th molecules/sq cm to 3.3 x 10 to the 14th molecules/sq cm. The time dependence of the decrease in NO correlated with solar activity, following the decline in solar activity from a solar maximum in 1979 to solar minimum in 1985-86. At middle and high latitudes, on the other hand, the NO concentration was found to be maximal in 1982-1983, a few years after the solar cycle maximum, and declined thereafter.

Mcpeters, R. D.↗

NASA NTRS1976

A mechanism for inducing climatic variations through ozone destruction: Screening of galactic cosmic rays by solar and terrestrial magnetic fields

A perturbation analysis, allowing for temperature and opacity feedbacks, is developed to calculate depletions in the O3 abundance and reductions of stratospheric solar heating that result from increases in NOx concentration. A pair of perturbation coefficients give the reduction in O3 and temperature through the stratosphere for a specified NOx increase. This type of analysis illustrates the tendency for various levels to self-heal when a perturbation occurs. Physical arguments indicate that the expected sign of the climatic effect is correct, with colder surface temperatures produced by reduced magnetic shielding. In addition, four qualitative reasons are suggested for thinking that significant ozone reductions by cosmic ray influxes will lead to an increased terrestrial albedo from stratospheric condensation. In this view, long-term (approximately 10,000 years) climatic changes have resulted from secular geomagnetic variations while shorter (approximately 100 years) excursions are related to changes in solar activity.

Chamberlain, J. W.↗