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At least 415 records · Page 23

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NASA NTRS1975

Interpretation of recent positron-electron measurements between 20 and 800 MeV

Recently measured positron and negatron spectra are discussed with regard to the problem of solar modulation. At energies above 180 MeV, the spherically symmetric Fokker-Planck equation with a diffusion coefficient proportional to particle rigidity provides reasonable fits to both the positron and total electron data. At energies below 180 MeV, the data are consistent with a continuation of the same diffusion coefficient and a local source of negatrons or with a change in the diffusion coefficient to a constant value.

Pellerin, C. J.↗

NASA NTRS1975

Further studies of the new component of cosmic rays at low energies

Recent observations with cosmic ray telescopes aboard the Pioneer 10 space probe have revealed an anomalous spectrum of nitrogen and oxygen nuclei relative to other nuclei such as carbon in the quiet time cosmic radiation below about 40 MeV/nuc. These observations are extended with additional data from Pioneer 10 and considerable new data from an identical telescope aboard Pioneer 11. In addition to the enhancement of nitrogen and oxygen nuclei observed earlier, the intensity of neon is enhanced as well. The spectra of boron, magnesium, and silicon appear to be similar to that of carbon. Data on the isotopic composition, solar modulation, and radial gradient of these nuclei are presented.

Webber, W. R.↗

NASA NTRS1976

Cosmic-ray positron and negatron spectra between 20 and 800 MeV measured in 1974

The flux density of cosmic-ray positrons and electrons was measured by a balloon-borne spark chamber magnetic spectrometer in two flights in an attempt to study the solar modulation of galactic cosmic rays. The total electron flux was found to be about 0.03/cu m/s/sr/MeV between 70 and 800 MeV and to increase toward lower energies, while the positron flux decreased sharply toward lower energies from about 0.008/cu m/s/sr/MeV at 650 MeV and only upper limits were obtained for positrons below 200 MeV. At energies above 180 MeV, the spherically symmetrical Fokker-Planck equation with a diffusion coefficient proportional to the particle rigidity provided a reasonable fit to both positron and total electron data, while at energies below 180 MeV, the data were consistent with a continuation of the same diffusion coefficient and local source of electrons, or a change in the diffusion coefficient to a constant value.

Hartman, R. C.↗

NASA NTRS1976

A quasi-linear kinetic equation for cosmic rays in the interplanetary medium

A kinetic equation for interplanetary cosmic rays is set up with the aid of weak-plasma-turbulence theory for an idealized radially symmetric model of the interplanetary magnetic field. As a starting point, this treatment invokes the Vlasov equation instead of the traditional Fokker-Planck equation. Quasi-linear theory is applied to obtain a momentum diffusion equation for the heliocentric frame of reference which describes the interaction of cosmic rays with convecting magnetic irregularities in the solar-wind plasma. Under restricted conditions, the well-known equation of solar modulation can be obtained from this kinetic equation.

Luhmann, J. G.↗

NASA NTRS1976

The isotopic composition of hydrogen and helium in low-energy cosmic rays

The isotopes H-2 and He-3 have been identified in low-energy cosmic rays during solar-quiet periods from 1973 January to 1974 October. These observations, made with the electron/isotope spectrometer on IMP-7, cover the energy intervals 5-29 MeV per nucleon for H-2 and 7-50 MeV per nucleon for He-3. The energy spectra of H-1, H-2, and He-3 fall rapidly with decreasing energy, giving H-2/H-1 and He-3/H-1 ratios which are essentially independent of energy as expected from current theories of the solar modulation of galactic cosmic rays. The measured He-4 spectrum, however, is essentially flat below 40 MeV per nucleon, suggesting that there may be contributions from a local, nonsolar source of He-4. Comparisons of the H-1, H-2, and He-3 observations with calculated spectra at 1 AU imply a mean interstellar path length of 7 plus or minus 2 g/sq cm. However, present low-energy measurements of H and He isotopes at 1 AU do not discriminate between possible cosmic-ray source spectra.

Mewaldt, R. A.↗

NASA NTRS1977

Sun-weather relationships

The possible processes in the lower atmosphere of the earth initiated or controlled by changes in the output of the sun are investigated. These changes can include solar variation in radiation (as in the constant, or in specific wavelength regions), in particles (as in physical properties of the solar wind, or in solar cosmic rays, or solar-modulated galactic cosmic rays), and in the extended magnetic field of the sun (as in circumstances of the passage of interplanetary sector boundaries). Changes of short term (in the weather) as well as long term (in regional or global climate) are considered.

Source record↗

NASA NTRS1978

Research in space physics at the University of Iowa

Specific fields of current investigation by satellite observation and ground-based radio-astronomical and optical techniques are discussed. Topics include: aspects of energetic particles trapped in the earth's magnetic field and transiently present in the outer magnetosphere and the solar, interplanetary, and terrestrial phenomena associated with them; plasma flows in the magnetosphere and the ionospheric effects of particle precipitation, with corresponding studies of the magnetosphere of Jupiter, Saturn, and possibly Uranus; the origin and propagation of very low frequency radio waves in the earth's magnetosphere and ionosphere; solar particle emissions and their interplanetary propagation and acceleration; solar modulation and the heliocentric radial dependence of the intensity of galactic cosmic rays; radio frequency emissions from the quintescent and flaring sun; shock waves in the interplanetary medium; radio emissions from Jupiter; and radio astronomy of pulsars, flare stars, and other stellar sources.

Vanallen, J. A.↗

NASA NTRS1977

The age of the galactic cosmic rays derived from the abundance of Be-10

Satellite measurements of the abundance of the Be-10 isotope in galactic cosmic rays are used to determine the cosmic-ray lifetime for escape. The data are analyzed by employing a technique based on an extensive calibration of a cosmic-ray telescope with the aid of high-energy Be beams accelerated in a bevatron. It is found that the Be-10/Be abundance ratio at 80 MeV/nucleon is 0.028 + or - 0.104. A comparison of this result with calculations based on a homogeneous steady-state model of galactic cosmic-ray confinement and propagation yields an average interstellar density of 0.18 (+0.18, -0.11) atom/cu cm and a corresponding cosmic-ray lifetime of 17 (+24, -8) million years after solar modulation is taken into account. The low average density traversed by the cosmic rays is shown to suggest that the particles may be spending the major part of their existence in regions of very low matter density. The consequences of these results are discussed for models of cosmic-ray propagation in the Galaxy, including such alternatives as propagation in a galactic halo or in regions of interstellar space where the interstellar gas density is very low.

Garcia-Munoz, M.↗

NASA NTRS1978

The medium energy cosmic ray experiment for ISEE-C

A description is provided of the medium energy cosmic ray experiment on board the ISEE-C spacecraft. This experiment is designed to measure the charge composition of nuclear energetic particles over wide ranges in energy (1-500 MeV/nucleon) and in charge (Z equals 1-28). Individual isotopes are resolvable for Z equals 1-7 over a restricted energy range. Electrons of 2-10 MeV are measured as well. These measurements are accomplished using all solid-state detector telescopes with detectors ranging in thickness from 15-3000 microns. The scientific goals of the experiment are also described. These include study of the composition of energetic particles from the sun and from the galaxy, the acceleration and flow of particles in the interplanetary medium, and electrons from Jupiter. Heliospheric gradients and other characteristics of solar modulation will be measured in conjunction with identical telescopes flown on the Voyager 1 and 2 spacecraft and similar telescopes on Pioneer 10 and 11.

Von Rosenvinge, T. T.↗

NASA NTRS1980

Solar array manufacturing industry simulation

Solar Array Manufacturing Industry Simulation (SAMIS) program is a standardized model of industry to manufacture silicon solar modules for use in electricity generation. Model is used to develop financial reports that detail requirements, including amounts and prices for materials, labor, facilities, and equipment required by companies.

Chamberlain, R. G.↗

NASA NTRS1978

Investigation of Test Methods, Material Properties, and Processes for Solar Cell Encapsulents

The technical activities were directed toward the assessment of encapsulation processes for use with ethylene/vinyl acetate copolymer as the pottant. Potentially successful formulations were prepared by compounding the raw polymer with ultraviolet absorbers and crosslinking agents to give stabilized and curable compositions. The compounded resin was then converted to a more useful form with an extruder to give pottant in sheets that could be more easily used in lamination. After experimenting with various techniques, the vacuum-bag process was found to be an excellent encapsulation method. Miniature single-celled and multi-celled solar modules of both substrate and superstrate designs were prepared by this technique. The resulting modules were of good appearance, were bubble-free, and successfully passed the thermal cycle test.

Source record↗

NASA NTRS1979

Integral Glass Encapsulation for Solar Arrays

Work reported was performed during the period from August 1977 to December 1978. The program objective was to continue the development of electrostatic bonding (ESB) as an encapsulation technique for terrestrial cells. Economic analyses shows that this process can be a cost-effective method of producing reliable, long lifetime solar modules. When considered in sufficient volume, both material and equipment costs are competitive with conventional encapsulation systems. In addition, the possibility of integrating cell fabrication into the encapsulation process, as in the case of the preformed cell contacts discussed in this report, offers the potential of significant overall systems cost reduction.

Younger, P. R.↗

NASA NTRS1979

High temperature - low mass solar blanket

Interconnect materials and designs for use with ultrathin silicon solar cells are discussed, as well as the results of an investigation of the applicability of parallel-gap resistance welding for interconnecting these cells. Data relating contact pull strength and cell electrical degradation to variations in welding parameters such as time, voltage and pressure are presented. Methods for bonding ultrathin cells to flexible substances and for bonding thin (75 micrometers) covers to these cells are described. Also, factors influencing fabrication yield and approaches for increasing yield are discussed. The results of vacuum thermal cycling and thermal soak tests on prototype ultrathin cell test coupons and one solar module blanket are presented.

Mesch, H. G.↗

NASA NTRS1978

Charge and energy spectra of heavy cosmic rays at intermediate energies

The energy spectra and the charge composition of the primary elements C, O, Ne, Mg, and Si have been measured in both the low-energy and high-energy modes of the University of Chicago telescope on board the IMP 8 spacecraft. Combining both modes of analysis yields differential energy spectra for each element from about 50 MeV/nucleon to about 1 GeV/nucleon. The charge ratios with respect to oxygen are found to be energy independent over this interval and are consistent with the results of cosmic-ray propagation and solar-modulation calculations. The relative abundances obtained are in substantial agreement with previous investigations in this energy regime.

Garcia-Munoz, M.↗

NASA NTRS1979

Propagation of a Forbush decrease in cosmic ray intensity to 15.9 AU

By observation of the large Forbush decrease in cosmic-ray intensity of April-May 1978 at heliocentric radial distances of 1.01, 6.97, and 15.91 AU, it is found that the causative magnetized plasma cloud moved outward from the sun at an apparent radial speed of about 960 km/s, independent of radial distance over this range. Recovery from the impulsive decrease in intensity was markedly slower at the larger distances. On the basis of this fact and other considerations, several tentative suggestions are made as to the large-scale nature of Forbush decreases and their relationship to the 11-year solar modulation of galactic cosmic-ray intensity.

Van Allen, J. A.↗

NASA NTRS1980

Solar coronal holes and cosmic ray intensity variations

A relationship between the (North-South) asymmetry in the areas of the solar polar coronal holes and the (North-South) anisotropy in the cosmic ray intensity is examined. The investigation was extended over a period of two years, using ground based observations of coronal brightness obtained by the K-Coronameter. Periods for study of cosmic ray variations were chosen maximizing the asymmetry of the polar coronal holes. The importance of the role played by coronal holes in the solar modulation of galactic cosmic rays is emphasized.

Venkatesan, D.↗

NASA NTRS1979

Analysis and evaluation in the production process and equipment area of the low-cost solar array project

Analyses of slicing processes and junction formation processes are presented. A simple method for evaluation of the relative economic merits of competing process options with respect to the cost of energy produced by the system is described. An energy consumption analysis was developed and applied to determine the energy consumption in the solar module fabrication process sequence, from the mining of the SiO2 to shipping. The analysis shows that, in current technology practice, inordinate energy use in the purification step, and large wastage of the invested energy through losses, particularly poor conversion in slicing, as well as inadequate yields throughout. The cell process energy expenditures already show a downward trend based on increased throughput rates. The large improvement, however, depends on the introduction of a more efficient purification process and of acceptable ribbon growing techniques.

Goldman, H.↗

NASA NTRS1980

Anti-reflection coatings on large area glass sheets

Antireflective coatings which may be suitable for use on the covers of photovoltaic solar modules can be easily produced by a dipping process. The coatings are applied to glass by drawing sheets of glass vertically out of dilute aqueous sodium silicate solutions at a constant speed, allowing the adherent liquid film to dry, then exposing the dried film to concentrated sulfuric acid, followed by a water rinse and dry. The process produces coatings of good optical performance (96.7 percent peak transmission at 0.540 mu M wavelength) combined with excellent stain and soil resistance, and good resistance to abrasion. The process is reproduceable and easily controlled.

Pastirik, E.↗