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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Preliminary design analysis for the solar optical telescope main mirror actuator

The resolution of the SOT Gregorian telescope was maintained if the conic foci of the elliptical secondary and parabolic primary were made to coincide within plus or minus 38 microns across the prime focus plane and to within 5 microns in focus. An error in coincidence across the focal plane caused all point images to show additional coma with all the comatic tails pointing in the same direction. An error in focus became magnified by the square of the magnification of the secondary and simply increased the diameter of the point source. Offsetting or rastering the sun may be accomplished by swinging the primary in an arc about the point of coincidence of the conic foci so long as the coincidence is kept to within the tolerance stated.

Dunn, R. B.↗
NASA NTRS1980

Analysis of the solar magnesium lines

The observed quiet-sun profiles for a number of Mg I and II lines are compared with theoretical spectra computed for two upper-photosphere lower-chromosphere models published by Ayres and Linsky (1976). Both the Mg I and the Mg II resonance line wings, observed with the University of Hawaii Echelle Rocket Spectrographs, favor a model with a higher temperature in the upper photosphere than required to match the visible region lines 4571 and 5172. Neither model atmosphere reproduces the observed shapes in the cores of the strong lines or the limb darkening of the 4571 A intercombination line. The wings of the ultraviolet lines in plages can be reproduced either with a mean one-component atmosphere or by a two-component model with an ad hoc filling factor.

Heasley, J. N.↗
NASA NTRS1981

The application of fracture mechanics to failure analysis of photovoltaic solar modules

Cracking of silicon solar cells and solar module transparent cover panels such as glass or polymethylmethacrylate (PMMA) is a major cause of photovoltaic solar module failure in field service. Silicon and cover materials are brittle, and cracking of these materials is expected to result from the extension of preexisting flaws under stress. Study of the cracking mechanisms is therefore an appropriate area for the application of fracture mechanics principles. In this study, fracture mechanics techniques were employed to identify the mode of crack propagation, to examine the fracture-initiating flaw, to estimate the nature and magnitude of fracture stress in the field, and to predict analytically the service lifetime. Recommendations for corrective actions are also made.

Chen, C. P.↗
NASA NTRS1986

Modeling and analysis of cascade solar cells

A brief review is given of the present status of the development of cascade solar cells. It is known that photovoltaic efficiencies can be improved through this development. The designs and calculations of the multijunction cells, however, are quite complicated. The main goal is to find a method which is a compromise between accuracy and simplicity for modeling a cascade solar cell. Three approaches are presently under way, among them (1) equivalent circuit approach, (2) numerical approach, and (3) analytical approach. Here, the first and the second approaches are discussed. The equivalent circuit approach using SPICE (Simulation Program, Integrated Circuit Emphasis) to the cascade cells and the cascade-cell array is highlighted. The methods of extracting parameters for modeling are discussed.

Ho, F. D.↗
NASA NTRS1985

An analysis of IRAS' solar system dust bands

Measurements of longitudinal variations in the brightness and in the latitude of the solar system dust bands recently discovered by IRAS will determine the orbital elements of the particles involved and may discriminate between cometary and asteroidal models of the origin of these bands. The expected variations for bands of dust particles with common orbital elements and small eccentricity and inclination are calculated as functions of semimajor axis.

Dermott, S. F.↗
NASA NTRS1986

Novel measurement techniques (development and analysis of silicon solar cells near 20% effciency)

Work in identifying, developing, and analyzing techniques for measuring bulk recombination rates, and surface recombination velocities and rates in all regions of high-efficiency silicon solar cells is presented. The accuracy of the previously developed DC measurement system was improved by adding blocked interference filters. The system was further automated by writing software that completely samples the unkown solar cell regions with data of numerous recombination velocity and lifetime pairs. The results can be displayed in three dimensions and the best fit can be found numerically using the simplex minimization algorithm. Also described is a theoretical methodology to analyze and compare existing dynamic measurement techniques.

Wolf, M.↗
NASA NTRS1988

Ray tracing optical analysis of offset solar collector for space station solar dynamic system

OFFSET, a detailed ray tracing computer code, was developed at NASA Lewis Research Center to model the offset solar collector for the Space Station solar dynamic electric power system. This model traces rays from 50 points on the face of the Sun to 10 points on each of the 456 collector facets. The triangular facets are modeled with spherical, parabolic, or toroidal reflective surface contour and surface slope errors. The rays are then traced through the receiver aperture to the walls of the receiver. Images of the collector and of the Sun within the receiver produced by this code provide insight into the collector receiver interface. Flux distribution on the receiver walls, plotted by this code, is improved by a combination of changes to aperture location and receiver tilt angle. Power loss by spillage at the receiver aperture is computed and is considerably reduced by using toroidal facets.

Jefferies, Kent S.↗
NASA NTRS1988

Ray tracing optical analysis of offset solar collector for Space Station solar dynamic system

OFFSET, a detailed ray tracing computer code, was developed at NASA Lewis Research Center to model the offset solar collector for the Space Station solar dynamic electric power system. This model traces rays from 50 points on the face of the sun to 10 points on each of the 456 collector facets. The triangular facets are modeled with spherical, parabolic, or toroidal reflective surface contour and surface slope errors. The rays are then traced through the receiver aperture to the walls of the receiver. Images of the collector and of the sun within the receiver produced by this code provide insight into the collector receiver interface. Flux distribution on the receiver walls, plotted by this code, is improved by a combination of changes to aperture location and receiver tilt angle. Power loss by spillage at the receiver aperture is computed and is considerably reduced by using toroidal facets.

Jefferies, Kent S.↗
NASA NTRS1989

Seismic analysis of the solar interior. I - Can opacity changes improve the theoretical frequencies?

The paper describes the application of seismic inverse theory to the deduction of properties of the solar interior using presently available measured frequencies of the solar oscillations. Only the solar opacity is included in this application. This study has used the spectral expansion method of Lanczos and Jackson to derive changes to the opacity which improve agreement between the theoretical and observed frequencies of oscillation. It is found that a family of opacity changes exists which yields models that improve the frequency agreement by amounts that are indistinguishable among the family members.

Korzennik, Sylvain G.↗
NASA NTRS1991

FIESTA ROC: A new finite element analysis program for solar cell simulation

The Finite Element Semiconductor Three-dimensional Analyzer by Ralph O. Clark (FIESTA ROC) is a computational tool for investigating in detail the performance of arbitrary solar cell structures. As its name indicates, it uses the finite element technique to solve the fundamental semiconductor equations in the cell. It may be used for predicting the performance (thereby dictating the design parameters) of a proposed cell or for investigating the limiting factors in an established design.

Clark, Ralph O.↗
NASA NTRS1990

Systems analysis of Mars solar electric propulsion vehicles

Mission performance, mass, initial power, and cost are determined for solar electric propulsion vehicles across a range of payload masses, reference powers, and mission trajectories. Thick radiation shielding is added to arrays using indium phosphide or III-V multijunction solar cells to reduce the damage incurred through the radiation belts. Special assessments of power management and distribution systems, atmospheric drag, and energy storage are made. It is determined that atmospheric drag is of no great concern and that the energy storage used in countering drag is unnecessary. A scheme to package the arrays, masts, and ion thrusters into a single fairing is presented.

Hickman, J. M.↗
NASA NTRS1996

Analysis of Cumulus Solar Irradiance Reflectance (CSIR) Events

Clouds are extremely important with regard to the transfer of solar radiation at the earth's surface. This study investigates Cumulus Solar Irradiance Reflection (CSIR) using ground-based pyranometers. CSIR events are short-term increases in solar radiation observed at the surface as a result of reflection off the sides of convective clouds. When sun-cloud observer geometry is favorable, these occurrences produce characteristic spikes in the pyranometer traces and solar irradiance values may exceed expected clear-sky values. Ultraviolet CSIR events were investigated during the summer of 1995 using Yankee Environmental Systems UVA-1 and UVB-1 pyranometers. Observed data were compared to clear-sky curves which were generated using a third degree polynomial best-fit line technique. Periods during which the observed data exceeded this clear-sky curve were identified as CSIR events. The magnitude of a CSIR event was determined by two different quantitative calculations. The MAC (magnitude above clear-sky) is an absolute measure of the difference between the observed and clear-sky irradiances. Maximum MAC values of 3.4 Wm(exp -2) and 0.069 Wm(exp -2) were observed at the UV-A and UV-B wavelengths, respectively. The second calculation determined the percentage above clear-sky (PAC) which indicated the relative magnitude of a CSIR event. Maximum UV-A and UV-B PAC magnitudes of 10.1% and 7.8%, respectively, were observed during the study. Also of interest was the duration of the CSIR events which is a function of sun-cloud-sensor geometry and the speed of cloud propagation over the measuring site. In both the UV-A and UV-B wavelengths, significant CSIR durations of up to 30 minutes were observed.

Laird, John L.↗
NASA NTRS2011

Time-Distance Analysis of Deep Solar Convection

Recently it was shown by Hanasoge, Duvall, and DeRosa (2010) that the upper limit to convective flows for spherical harmonic degrees l<? is considerably smaller than the flows predicted by the ASH simulations (Miesch et a7. ref) at the depth r/R=0.95 ' The deep-focusing Lime-distance technique used to develop the upper limit was applied to linear acoustic simulations of a solar interior perturbed by convective flows in order to calibrate the technique. This technique has been applied to other depths in the convection zone and the results will be presented. The deep-focusing technique has considerable sensitivity to the flow ' signals at the desired subsurface location ' However, as shown by Birch {ref}, there is remaining much sensitivity to near-surface signals. Modifications to the technique using multiple bounce signals have been examined in a search for a more refined sensitivity, or kernel function. Initial results are encouraging and results will be presented'

Duvall, T. L., Jr.↗
NASA NTRSDate not supplied

Direct Analysis of Early Solar System Aqueous Fluids by TOF-SIMS

We lack fundamental information related to the location and timing of the aqueous alteration in the early solar system, and the detailed nature of the aqueous fluid itself [1,2,3]. Two thermally-metamorphosed ordinary chondrite regolith breccias (Monahans 1998, hereafter simply “Monahans” (H5) and Zag (H3-6)) contain fluid inclusion-bearing halite (NaCl) crystals [4,5]. The halites were dated by K-Ar, Rb-Sr and I-Xe systematics to be ~4.5 billion years old [4,6,7] and thus the trapped aqueous fluids are at least as ancient. Through previously-published O, H, Cr isotopic work we have established that the fluid-bearing halite originated in the outer solar system[8].

M Zolensky↗