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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 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
NASA NTRS2008

Hyperspectral Sun Photometer for Atmospheric Characterization and Vicarious Calibrations

A hyperspectral sun photometer and associated methods have been developed and demonstrated. Accurate sun photometer calibration is critical to properly measure the solar irradiance and characterize the atmosphere. Traditional sun photometer calibration requires solar observations over several hours. In contrast, the procedures for operating this photometer entail less data acquisition time and embody a more direct approach to calibration. The scientific value of the measurement data produced by this instrument is not adversely affected by atmospheric instability. In addition, this instrument yields hyperspectral data covering a large spectral range (350-2,500 nm) not available from most traditional sun photometers. The hyperspectral sun photometer components include (1) a commercially available spectroradiometer that has been laboratory-calibrated and (2) a commercially available reflectance standard panel that exhibits nearly Lambertian 99% reflectance. The spectroradiometer is positioned above, and aimed downward at, the panel. The procedure for operating this instrument calls for a series of measurements: one in which the panel is fully illuminated by the sun, one in which a shade is positioned between the panel and the sun, and two in which the shade is positioned to cast a shadow to either side of the panel. The total sequence of measurements can be performed in less than a minute. From these measurements, the total radiance, the diffuse radiance, and the direct solar radiance are calculated. The direct solar irradiance is calculated from the direct solar radiance and the known reflectance factor of the panel as a function of the solar zenith angle. Atmospheric characteristics are estimated from the optical depth at various wavelengths calculated from (1) the direct solar irradiance obtained as described above, (2) the air mass along a column from the measurement position to the Sun, and (3) the top-of-atmosphere solar irradiance. The instrumentation used to implement the sun photometer is the same as that used to characterize targets used in radiometric vicarious calibrations. Utilizing this type of sun photometer thus reduces the amount of instrumentation and labor required to perform these studies.

Pagnutti, Mary↗
NASA NTRS1972

Junction characteristics of silicon solar cells. Part 1: Nonilluminated case

Precise values of the reverse saturation currents in silicon solar cells and magnitudes of the diffusion and recombination components have been obtained. The recombination current as well as leakage current due to shunting are shown to be nonuniform across the cell. The diffusion lengths calculated from the diffusion current components agree well with diffusion lengths measured independently in similar material. Models are given demonstrating the effect of recombination and shunting currents on the dark current-voltage characteristics of solar cells.

Stirn, R. J.↗
NASA NTRS1984

Radiation tolerance of low resistivity, high voltage silicon solar cells

The radiation tolerance of the following three low resistivity, high voltage silicon solar cells was investigated: (1) the COMSAT MSD (multi-step diffused) cell, (2) the MinMIS cell, and (3) the MIND cell. A description of these solar cells is given along with drawings of their configurations. The diffusion length damage coefficients for the cells were calculated and presented. Solar cell spectral response was also discussed. Cells of the MinMIS type were judged to be unsuitable for use in the space radiation environment.

Weizer, V. G.↗
NASA NTRS1993

Satellite measurements of the backscattered ultraviolet to determine ozone trends, volcanic SO2, and nitric oxide

Measurements of the atmospheric backscattered UV albedo have been used from satellites for more than 20 years to measure ozone. The longest continuous record has been from the Solar Backscattered Ultraviolet instrument (SBUV) and TOMS on the Nimbus 7 satellite, which have been in operation since November of 1978. Because of degradation in space of the diffuser plate used to measure extraterrestrial solar flux, it has been necessary to develop new techniques to maintain the calibration of these instruments. Calibration is maintained by requiring that ozone measured by different wavelength pairs be consistent, and by requiring that ozone measured at different solar zenith angles be consistent. This technique of using a geophysical quantity, ozone, as a transfer standard for wavelength calibration is very powerful. The recalibrated data have been used to measure total ozone trends to an accuracy of +/- 1.3 percent 2(sigma) error over ten years. No significant trends are found near the equator, but significant trends larger than predicted by homogeneous chemistry are found at middle to high latitudes in both hemispheres. In addition, UV albedo data have been used to measure SO2 using band structure in the 300-310 nm range, and to measure nitric oxide in the upper stratosphere and mesosphere using the (10) and (02) NO gamma band fluorescence features.

Mcpeters, Richard↗
NASA NTRS1980

Grain size dependence of silicon solar cell parameters

Measurements of the non-uniform diffusion length of the minority carriers near grain boundaries in polycrystalline silicon have been used to develop an analytical model for the calculation of solar cell output as a function of grain size. Experimental results are presented which verify the theoretical analysis. Variation of open circuit voltage and fill factor with grain size is discussed.

Koliwad, K. M.↗
NASA NTRS1993

Diffusion length variation and proton damage coefficients for InP/In(x)Ga(1-x)As/GaAs solar cells

Indium phosphide solar cells are more radiation resistant than gallium arsenide and silicon solar cells, and their growth by heteroepitaxy offers additional advantages leading to the development of lighter, mechanically strong and cost-effective cells. Changes in heteroepitaxial InP cell efficiency under 0.5 and 3 MeV proton irradiations are explained by the variation in the minority-carrier diffusion length. The base diffusion length versus proton fluence is calculated by simulating the cell performance. The diffusion length damage coefficient K(L) is plotted as a function of proton fluence.

Jain, R. K.↗
NASA NTRS1970

Astrophysics and astronomy

Infrared and ultraviolet spectroscopy of solar radiation, astrophysics, and interplanetary diffusion

Source record↗
NASA NTRS1973

Physical phenomena related to crystal growth in the space environment

The mechanism of crystal growth which may be affected by the space environment was studied. Conclusions as to the relative technical and scientific advantages of crystal growth in space over earth bound growth, without regard to economic advantage, were deduced. It was concluded that the crucibleless technique will most directly demonstrate the unique effects of the greatly reduced gravity in the space environment. Several experiments, including crucibleless crystal growth using solar energy and determination of diffusion coefficients of common dopants in liquid silicon were recommended.

Chu, T. L.↗
NASA NTRS1978

Chemical vapor deposition growth

The objective was to investigate and develop chemical vapor deposition (CVD) techniques for the growth of large areas of Si sheet on inexpensive substrate materials, with resulting sheet properties suitable for fabricating solar cells that would meet the technical goals of the Low Cost Silicon Solar Array Project. The program involved six main technical tasks: (1) modification and test of an existing vertical-chamber CVD reactor system; (2) identification and/or development of suitable inexpensive substrate materials; (3) experimental investigation of CVD process parameters using various candidate substrate materials; (4) preparation of Si sheet samples for various special studies, including solar cell fabrication; (5) evaluation of the properties of the Si sheet material produced by the CVD process; and (6) fabrication and evaluation of experimental solar cell structures, using impurity diffusion and other standard and near-standard processing techniques supplemented late in the program by the in situ CVD growth of n(+)/p/p(+) sheet structures subsequently processed into experimental cells.

Ruth, R. P.↗
NASA NTRS1978

Crustal evolution inferred from Apollo magnetic measurements

The topology of lunar remanent fields is investigated by analyzing simultaneous magnetometer and solar wind spectrometer data. The diffusion model proposed by Vanyan (1977) to describe the field-plasma interaction at the lunar surface is extended to describe the interaction with fields characterized by two scale lengths, and the extended model is compared with data from three Apollo landing sites (Apollo 12, 15 and 16) with crustal fields of differing intensity and topology. Local remanent field properties from this analysis are compared with high spatial resolution magnetic maps obtained from the electron reflection experiment. It is concluded that remanent fields over most of the lunar surface are characterized by spatial variations as small as a few kilometers. Large regions (50 to 100 km) of the lunar crust were probably uniformly magnetized early in the evolution of the crust. Smaller scale (5 to 10 km) magnetic sources close to the surface were left by bombardment and subsequent gardening of the upper layers of these magnetized regions. The small scale sized remanent fields of about 100 gammas are measured by surface experiments, whereas the larger scale sized fields of about 0.1 gammas are measured by the orbiting subsatellite experiments.

Dyal, P.↗
NASA NTRS1983

Gettering Silicon Wafers with Phosphorus

Silicon wafers subjected to gettering in phosphorus atmosphere have longer diffusion lengths and higher solar-cell efficiencies than untreated wafers. Gettering treatment improves properties of solar cells manufactured from impure silicon and is compatible with standard solar-cell processing.

Daiello, R. V.↗
NASA NTRS1981

Apparatus and technique for pulsed electron beam annealing for solar cell production

Many of the demands of high-throughput processing of solar cells can be satisfied by transient methods using pulsed electron beams. A prototype pulsed electron beam processor for solar cell production has been built, and is intended for automated annealing of solar cell junction ion implantation at a rate of 1200-1800 silicon wafers per hour. Other applications include solar cell junctions by pulse diffusion, annealing of ion-implanted back surface fields, and pulse sintering of cell metallization.

Landis, G. A.↗
NASA NTRS1988

Molecular-Beam-Epitaxy Program

Molecular Beam Epitaxy (MBE) computer program developed to aid in design of single- and double-junction cascade cells made of silicon. Cascade cell has efficiency 1 or 2 percent higher than single cell, with twice the open-circuit voltage. Input parameters include doping density, diffusion lengths, thicknesses of regions, solar spectrum, absorption coefficients of silicon (data included for 101 wavelengths), and surface recombination velocities. Results include maximum power, short-circuit current, and open-circuit voltage. Program written in FORTRAN IV.

Sparks, Patricia D.↗
NASA NTRS1990

Molecular clouds without detectable CO

The clouds identified by Desert, Bazell, and Boulanger (DBB clouds) in their search for high-latitude molecular clouds were observed in the CO (J = 1-0) line, but only 13 percent of the sample was detected. The remaining 87 percent are diffuse molecular clouds with CO abundances of about 10 to the -6th, a typical value for diffuse clouds. This hypothesis is shown to be consistent with Copernicus data. The DBB clouds are shown to ben an essentially complete catalog of diffuse molecular clouds in the solar vicinity. The total molecular surface density in the vicinity of the sun is then only about 20 percent greater than the 1.3 solar masses/sq pc determined by Dame et al. (1987). Analysis of the CO detections indicates that there is a sharp threshold in extinction of 0.25 mag before CO is detectable and is derived from the IRAS I(100) micron threshold of 4 MJy/sr. This threshold is presumably where the CO abundance exhibits a sharp increase

Blitz, Leo↗
NASA NTRS1991

The transient gamma-ray spectrometer

The authors describe the Transient Gamma-Ray Spectrometer (TGRS) to be flown onboard the WIND spacecraft. This instrument is designed to detect cosmic gamma-ray bursts over the energy range of 20 keV to 10 MeV with an expected spectroscopic resolution of 2 keV at 1 MeV (E/Delta-E = 500). The active detection element is a 215-cu cm high-purity n-type Ge crystal cooled to cryogenic temperatures by a passive radiative cooler. The geometric field of view (FOV) defined by the cooler is 170 deg FWFM. Burst data are stored directly in an onboard 2.75-Mb burst memory with an absolute timing accuracy of +/-1.5 ms. This capacity is sufficient to store the entire spectral data set of all but the largest bursts. In addition to burst measurements, the instrument will also study solar flares, search for possible diffuse background lines, and monitor the 511-keV positron annihilation radiation from the galactic center. The experiment is scheduled to be launched on a Delta II launch vehicle from Cape Canaveral on December 31, 1992.

Owens, A.↗
NASA NTRS1991

An observation of a heliospheric magnetic cycle dependence for the integral radial gradient of E above 60 MeV cosmic rays

The dependence of the integral radial gradient of the cosmic radiation upon the cosmic ray intensity level and heliocentric radial distance is investigated. The magnitude of the integral radial gradient (IRG) from 1982-1990, during a period of negative polarity, is a strong function of the cosmic ray intensity changing from about 1.5 percent/AU at the time of the peak intensity in 1987 to about 3 percent/AU at times of minimum intensity in 1982 and 1990. In the early period studied from 1977 to 1982, during a period of positive polarity, practically no dependence of the magnitude of the IRG on the cosmic ray intensity was found. The gradient remained at about 3 percent/AU during the entire period. It is argued that these specific changes in the behavior of the gradient in opposite polarity cycles are not predicted by either the drift-wavy current sheet or simple diffusion-convection models of the solar modulation. The results are discussed in the context of the present understanding of the causes of the asymmetry in the 11-year modulation cycles.

Webber, W. R.↗