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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Effects of proton irradiation on several spacecraft science components.

In connection with programs for the exploration of the outer planets, several models have been developed and used to analyze the radiation hazard to the spacecraft. Typical components found in space flight science instruments have been tested to determine their capability to function properly before, after and, in some cases during, exposures to energy equivalenced levels predicted by the models. A summary of proton-irradiation tests is provided.

Parker, R. H.↗
NASA NTRS1976

Effects of neutron irradiation on the characteristics of a buried channel CCD at 80 degrees Kelvin and 295 degrees Kelvin

Buried channel CCD shift registers were irradiated with 15 MeV neutrons. The irradiations were performed at 80 K and 295 K on operating devices with normal clocks and bias voltages applied. Dark current increased from the pre-irradiation value of 7 nA/sq cm to 1,600 nA/sq cm at 1 x 10 to the 13th power n/sq cm. The input gate threshold shift observed at 80K was minus 0.9 volts per 10 to the 13th power n/sq cm, a factor of 4 less than that predicted from a first order calculation of the equivalent ionization dose of neutrons in the oxide. Transfer efficiency measurements yielded a bulk electron trap creation rate for neutron irradiation of 14.0 cm to the minus 1 power at 295 K with a trap emission time constant of 25 microseconds.

Saks, N. S.↗
NASA NTRS1979

Effects of electron irradiation on large insulating surfaces used for European Communications Satellites

Samples of aluminized Kapton used for passive thermal control on the VHF shield and the antenna dish of ESA's OTS satellite and its derivatives were subjected to an incident electron beam of 25 keV and irradiated for 8 hours at room temperature and at -173 C under a vacuum of the 10 to the minus 6 th power torr. Visual observations during electron irradiation, measurements of leakage current and discharge characteristics, and material degradation following completion of irradiation are discussed.

Reddy, J.↗
NASA NTRS1978

Effect of ultrasonic irradiation on mammalian cells and chromosomes in vitro

Human peripheral blood and HeLa cells were irradiated in vitro at the ultrasonic frequency of 65 kHz. The whole blood and HeLa cell suspensions were exposed to continuous and pulsed ultrasonic power levels of 0.12, 0.16, 0.72, 1.12 and 2.24 W for a period of one minute. The method of ultrasonic irradiation was carried out with the whole blood or HeLa cell suspensions coupled directly to a cylindrical transducer while heating of the cell suspensions in excess of 41 C was avoided. Irradiated and unirradiated peripheral blood lymphocyte chromosome cultures were prepared and scored for selected numerical and morphological aberrations. There was no significant difference in the frequency of chromosomal aberrations between irradiated and unirradiated cells.

Roseboro, J. A.↗
NASA NTRS1980

Effect of UV irradiation on evaporated ZnS films

Evaporated ZnS films used as a component in reflectance enhancing or decreasing multilayer coatings for mirrors, transparent optical materials, and vacuum UV reflecting optics, are investigated with reference to the reflectance loss under UV irradiation and the formation of ZnO as a result of the decomposition of ZnS in the presence of oxygen. Reflectance measurements over a broad wavelength range reveal that the UV induced reflectance losses are generally restricted to wavelengths shorter than 4000 A and are most severe in the vacuum UV region. After 134 hr of UV exposure initially polycrystalline film of 150-200 A thick is completely converted to amorphous ZnO. The results demonstrate that caution should be exercised in employing ZnS as the outer layer in an optical coating system designed for use in the UV and vacuum UV regions.

Hass, G.↗
NASA NTRS1991

Effects of proton irradiation on the performance of InP/GaAs solar cells

InP solar cells are known to be more radiation resistant than either GaAs or Si. In addition, AMO total area efficiencies approaching 19 percent were attained for InP. However, the present high substrate cost presents a barrier to the eventual widespread use of InP cells in space. In addition, if cell thinning becomes desirable, their relative fragility presents a problem. For these reasons, the NASA Lewis Research Center has initiated a program, aimed at producing thin InP cells, by heteroepitaxial deposition of InP on cheaper, more durable substrates. To date, a short term feasibility study as Spire has resulted in cells processed from InP heteroepitaxially deposited on Si substrates with an intervening thin GaAs layer (InP/GaAs/Si) and cells produced from InP deposited on GaAs (InP/GaAs). As a result of this short study efficiencies of over 7 and 9 percent were achieved for InP/GaAs/Si and InP/GaAs respectively. Although these efficiencies are low, they represent a modest and encouraging starting point for a more intensive program. Obviously, when considering economy and mechanical strength, cells processed on silicon substrates are preferred. However, although the InP/GaAs cells are not the final desirable products of this program, their properties serve to highlight several roadblocks to be overcome in producing cells with the more desirable cost and strength properties. Hence, in the present case, the properties of the InP/GaAs cells before and after irradiation by 10 MeV protons are examined. A similar study of InP/GaAs/Si cells will be reported on at a later date.

Weinberg, Irving↗
NASA NTRS1991

Neutron, gamma ray and post-irradiation thermal annealing effects on power semiconductor switches

Experimental data showing the effects of neutrons and gamma rays on the performance characteristics of power-type NPN bipolar junction transistors (BJTs), metal-oxide-semiconductor field effect transistors (MOSFETs), and static induction transistors (SITs) are given. These three types of devices were tested at radiation levels which met or exceeded the SP-100 requirements. For the SP-100 radiation requirements, the BJTs were found to be most sensitive to neutrons, the MOSFETs were most sensitive to gamma rays, and the SITs were only slightly sensitive to neutrons. Postirradiation thermal anneals at 300 K and up to 425 K were done on these devices and the effectiveness of these anneals are also discussed.

Schwarze, G. E.↗
NASA NTRS1995

Effect of neutron irradiation on the London penetration depth for polycrystalline Bi(1.8)Pb(0.3)Sr2Ca2Cu3O10 superconductor

Magnetization studies of polycrystalline Bi(1.8)Pb(0.3)Sr2Ca2Cu3O10 superconductor, prior to and after neutron irradiation, showed an increase in J(sub c) due to irradiation damage. Analysis of the equilibrium magnetization revealed significant increases in other more fundamental properties. In particular, the London penetration depth increased by approximately 15 percent following irradiation with 8 x 10(exp 16) neutrons/sq cm. Corresponding changes were observed in the upper critical magnetic field H(sub c2). However, the most fundamental thermodynamic property, the superconductive condensation energy F(sub c), was unaffected by the moderate level of neutron-induced damage.

Ossandon, J. G.↗
NASA NTRS2001

Simulation Study of Effects of Solar Irradiance and Sea Surface Temperature on Monsoons and Global Circulation

A recent version of the GEOS 2 GCM was used to isolate the roles of the annual cycles of solar irradiation and/or sea-surface temperatures (SSTs) on the simulated circulation and rainfall. Four 4-year long integrations were generated with the GCM. The first integration, called Control Case, used daily-interpolated SSTs from a 30 year monthly SST climatology that was obtained from the analyzed SST-data, while the solar irradiation at the top of the atmosphere was calculated normally at hourly intervals. The next two cases prescribed the SSTs or the incoming solar irradiance at the top of the atmosphere at their annual mean values, respectively while everything else was kept the same as in the Control Case. In this way the influence of the annual cycles of both external forcings was isolated.

Sud, Y. C.↗
NASA NTRS2016

Directional and Spectral Irradiance in Ocean Models: Effects on Simulated Global Phytoplankton, Nutrients, and Primary Production

The importance of including directional and spectral light in simulations of ocean radiative transfer was investigated using a coupled biogeochemical-circulation-radiative model of the global oceans. The effort focused on phytoplankton abundances, nutrient concentrations and vertically-integrated net primary production. The importance was approached by sequentially removing directional (i.e., direct vs. diffuse) and spectral irradiance and comparing results of the above variables to a fully directionally and spectrally-resolved model. In each case the total irradiance was kept constant; it was only the pathways and spectral nature that were changed. Assuming all irradiance was diffuse had negligible effect on global ocean primary production. Global nitrate and total chlorophyll concentrations declined by about 20% each. The largest changes occurred in the tropics and sub-tropics rather than the high latitudes, where most of the irradiance is already diffuse. Disregarding spectral irradiance had effects that depended upon the choice of attenuation wavelength. The wavelength closest to the spectrally-resolved model, 500 nm, produced lower nitrate (19%) and chlorophyll (8%) and higher primary production (2%) than the spectral model. Phytoplankton relative abundances were very sensitive to the choice of non-spectral wavelength transmittance. The combined effects of neglecting both directional and spectral irradiance exacerbated the differences, despite using attenuation at 500 nm. Global nitrate decreased 33% and chlorophyll decreased 24%. Changes in phytoplankton community structure were considerable, representing a change from chlorophytes to cyanobacteria and coccolithophores. This suggested a shift in community function, from light-limitation to nutrient limitation: lower demands for nutrients from cyanobacteria and coccolithophores favored them over the more nutrient-demanding chlorophytes. Although diatoms have the highest nutrient demands in the model, their relative abundances were generally unaffected because they only prosper in nutrient-rich regions, such as the high latitudes and upwelling regions, which showed the fewest effects from the changes in radiative simulations. The results showed that including directional and spectral irradiance when simulating the ocean light field can be important for ocean biology, but the magnitude varies with variables and regions. The quantitative results are intended to assist ocean modelers when considering improved irradiance representations relative to other processes or variables associated with the issues of interest.

Phytoplankton↗
NASA NTRS2017

Analyzing the Chemical and Spectral Effects of Pulsed Laser Irradiation to Simulate Space Weathering of a Carbonaceous Chondrite

Space weathering processes alter the chemical composition, microstructure, and spectral characteristics of material on the surfaces of airless bodies. The mechanisms driving space weathering include solar wind irradiation and the melting, vaporization and recondensation effects associated with micrometeorite impacts e.g., [1]. While much work has been done to understand space weathering of lunar and ordinary chondritic materials, the effects of these processes on hydrated carbonaceous chondrites is poorly understood. Analysis of space weathering of carbonaceous materials will be critical for understanding the nature of samples returned by upcoming missions targeting primitive, organic-rich bodies (e.g., OSIRIS-REx and Hayabusa 2). Recent experiments have shown the spectral properties of carbonaceous materials and associated minerals are altered by simulated weathering events e.g., [2-5]. However, the resulting type of alteration i.e., reddening vs. bluing of the reflectance spectrum, is not consistent across all experiments [2-5]. In addition, the microstructural and crystal chemical effects of many of these experiments have not been well characterized, making it difficult to attribute spectral changes to specific mineralogical or chemical changes in the samples. Here we report results of a pulsed laser irradiation experiment on a chip of the Murchison CM2 carbonaceous chondrite to simulate micrometeorite impact processing.

Thompson, M. S.↗
NASA NTRS1971

Neutron capture effects in lunar gadolinium and the irradiation histories of some lunar rocks.

The Gd isotopic composition in 19 lunar rock and soil samples from three Apollo sites is reported. The analytical techniques and the high precision mass spectrometric measurements are discussed. Enrichments in the Gd-158 oxide to G-157 oxide ratio due to neutron capture range up to 0.75%. Integrated 'thermal' neutron fluxes derived from the isotopic anomalies of Gd are compared with spallation Kr data from aliquot samples to construct a model which gives both average cosmic-ray irradiation depths and effective neutron exposure ages for some rocks. Rock 14310 is the first lunar sample where Kr anomalies due to resonance neutron capture in Br are observed. A Kr-81/Kr exposure age of 262 (plus or minus 7)m.y. is calculated for this rock.

Lugmair, G. W.↗