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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 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Seasonal and nonseasonal variability of satellite-derived surface pigment concentration in the California Current

The large-scale patterns of satellite-derived surface pigment concentration off the west coast of North America are presented and are averaged into monthly mean surface wind fields over the California Current system (CCS) for the July 1979 to June 1986 period. The patterns are discussed in terms of both seasonal and nonseasonal variability for the indicated time period. The large-scale seasonal characteristics of the California Current are summarized. The data and methods used are described, and the problems known to affect the satellite-derived pigment concentrations and the wind data used in the study are discussed. The statistical analysis results are then presented and discussed in light of past observations and theory. Details of the CZCS data processing are described, and details of the principal estimator pattern methodology used here are given.

Strub, P. Ted↗
NASA NTRS1990

A volatile organics concentrator for use in monitoring Space Station water quality

The process used to identify, select, and design an approach to the isolation and concentration of volatile organic compounds from a water sample prior to chemical analysis in a microgravity environment is discerned. The trade analysis leading to the recommended volatile organics concentrator (VOC) concept to be tested in a breadboard device is presented. The system covers the areas of gases, volatile separation from water, and water removal/gas chromatograph/mass spectrometer interface. Five options for potential use in the VOC and GC/MS system are identified and ranked, and also nine options are presented for separation of volatiles from the water phase. Seven options for use in the water removal/GC column and MS interface are also identified and included in the overall considerations. A final overall recommendation for breadboard VOC testing is given.

Ehntholt, Daniel J.↗
NASA NTRS1990

Long-term trends in the concentrations of SF6, CHClF2, and COF2 in the lower stratosphere from analysis of high-resolution infrared solar occultation spectra

Long-term trends in the concentrations of SF6, CHClF2 in the lower stratosphere are derived using results from analyses of the 1980 and of several more recently obtained IR solar occultation spectra. Results show that the increase rates of SF6 and CHClF2 were about 7.4/yr and 9.4/yr, respectively, which correspond to cumulative increases by factors of about 1.7 and 2.0 in the concentrations of these gases over the 7.2 yr measurement period. The average increase rate for COF2 was 10.3/yr over the same time period. The present results are compared with previously reported observations and trends and with one-dimensional model calculations.

Rinsland, C. P.↗
NASA NTRS1990

Wide acceptance angle, high concentration ratio, optical collector

The invention is directed to an optical collector requiring a wide acceptance angle, and a high concentration ratio. The invention is particularly adapted for use in solar collectors of cassegrain design. The optical collector system includes a parabolic circular concave primary mirror and a hyperbolic circular convex secondary mirror. The primary mirror includes a circular hole located at its center wherein a solar collector is located. The mirrored surface of the secondary mirror has three distinct zones: a center circle, an on-axis annulus, and an off-axis section. The parabolic shape of the primary mirror is chosen so that the primary mirror reflects light entering the system on-axis onto the on-axis annulus. A substantial amount of light entering the system off-axis is reflected by the primary mirror onto either the off-axis section or onto the center circle. Subsequently, the off-axis sections reflect the off-axis light toward the solar collector. Thus, off-axis light is captured which would otherwise be lost to the system. The novelty of the system appears to lie in the configuration of the primary mirror which focuses off-axis light onto an annular portion of the secondary mirror to enable capture thereof. This feature results in wide acceptance angle and a high concentration ratio, and also compensates for the effects of non-specular reflection, and enables a cassegrain configuration to be used where such characteristics are required.

Kruer, Mark Arthur↗
NASA NTRS1991

AlGaAs top solar cell for mechanical attachment in a multi-junction tandem concentrator solar cell stack

The AstroPower self-supporting, transparent AlGaAs top solar cell can be stacked upon any well-developed bottom solar cell for improved system performance. This is an approach to improve the performance and scale of space photovoltaic power systems. Mechanically stacked tandem solar cell concentrator systems based on the AlGaAs top concentrator solar cell can provide near term efficiencies of 36 percent (AMO, 100x). Possible tandem stack efficiencies greater than 38 percent (100x, AMO) are feasible with a careful selection of materials. In a three solar cell stack, system efficiencies exceed 41 percent (100x, AMO). These device results demonstrate a practical solution for a state-of-the-art top solar cell for attachment to an existing, well-developed solar cell.

Dinetta, L. C.↗
NASA NTRS1991

Tandem concentrator solar cells with 30 percent (AMO) power conversion efficiency

Very high efficiency concentrator solar panels are envisioned as economical and reliable electrical power subsystems for space based platforms of the future. GaAs concentrator cells with very high efficiencies and good sub-bandgap transmissions can be fabricated on standard wafers. GaSb booster cell development is progressing very well; performance characteristics are still improving dramatically. Consistent GaAs/GaSb stacked cell AMO efficiencies greater than 30 percent are expected.

Avery, J. E.↗
NASA NTRS1991

Mini-dome Fresnel lens photovoltaic concentrator development

Since 1986 work on a new high-performance, light-weight space photovoltaic concentration array has been conducted. An update on the mini-dome lens concentrator array development program is provided. Recent prototype cell and lens test results indicate that near-term array performance goals of 300 w/sq m and 100 w/kg are feasible, and that a longer-term goal of 200 w/kg is reasonable.

Oneill, Mark J.↗
NASA NTRS1991

Fourier transform infrared and Raman spectroscopic characterization of homogeneous solution concentration gradients near a container wall at different temperatures

Fourier transform infrared (FTIR) and Raman spectroscopic techniques were used to study the solution concentration gradient in succino nitrile-rich and water-rich homogeneous solutions. The spectroscopic data shows significant concentration dependency. Although FTIR-attenuated total reflectance could not yield surface spectra since the evanescent infrared wave penetrated deep into the bulk solution, it showed that water-rich clusters were decreased at higher temperatures. This result is consistent with the calorimetric results reported earlier.

Loo, B. H.↗
NASA NTRS1991

Impedances of nickel electrodes cycled in various KOH concentrations

Recent tests at Hughes have shown that Ni/H2 cells cycled in 26 percent KOH have much longer lives than those cycled in other concentrations. As part of an ongoing program to try to correlate the impedances of nickel electrodes with their life and performance, impedances were measured of a number of electrodes from these tests that had been cycled in concentrations from 21 to 36 percent KOH. These had ranged from about 1000 to 40,000 cycles. After cycling ten times to reduce possible changes due to storage, impedances were measured at five voltages corresponding to low states of charge. The results were analyzed using a standard circuit model including Warburg impedance term. Lower kinetic resistances and Warburg slopes were found for several electrodes which had been cycled in 26 percent KOH even though they had been cycled for a much longer time than the others. Interpretation of the data is complicated by the fact that the cycle lives, storage times, and failure mechanisms varied. Several other circuit models have also been examined, but the best correlations with life were found with parameters obtained from the simple model.

Margaret A Reid↗
NASA NTRS1990

High pressure-temperature electrical conductivity of magnesiowustite as a function of iron oxide concentration

The electrical conductivity of (Mg, Fe)O magnesiowustite containing 9 and 27.5 mol pct FeO has been measured at simultaneously high pressures (30-32 GPa) and temperatures using a diamond anvil cell heated with a continuous wave Nd:YAG laser and an external resistance heater. The conductivity depends strongly on the FeO concentration at both ambient and high pressures. At the pressures and temperatures of about 30 GPa and 2000 K, conditions expected in the lower mantle, the magnesiowustite containing 27.5 percent FeO is 3 orders of magnitude more conductive than that containing 9 percent FeO. The activation energy of magnesiowustite decreases with increasing iron concentration from 0.38 (+ or - 0.09) eV at 9 percent FeO to 0.29 (+ or - 0.05) eV at 27.5 percent FeO.

Li, Xiaoyuan↗
NASA NTRS1990

Lightweight concentrator module with 30 percent AM0 efficient GaAs/GaSb tandem cells

A concept is presented for an aerospace concentrator module with lightweight domed lenses and 30 percent AM0 efficient GaAs/GaSb tandem solar cell circuits. The performance of transparent GaAs cells is reviewed. NASA's high-altitude jet flight calibration data for recent GaSb cells assembled with bulk GaAs filters are reported, along with subsequent Boeing and NASA measurements of GaSb I-V performance at various light levels and temperatures. The expected performance of a basic two-terminal tandem concentrator circuit with three-to-one voltage matching is discussed. All of the necessary components being developed to assemble complete flight test coupons are shown. Straightforward interconnect and assembly techniques yield voltage matched circuits with near-optimum performance over a wide temperature range.

Avery, J. E.↗
NASA NTRS1990

23.5 percent thin-film space concentrator cells

Thin-film AlGaAs-GaAs double-heterostructure concentrator cells were fabricated which exhibit total-area conversion efficiencies as high as 23.5 percent AM0 at 100 suns, 25 C. This is one of the best space concentrators measured to date at NASA and is designed for a thin-film cell without a prismatic coverglass. This solar cell structure consists of a GaAs/AlGaAs film less than 5 micron thick mounted to a glass cover/superstrate, with coplanar back-side contacts. The coverglass is not prismatic. The CLEFT process, a method for mechanically separating epitaxial layers from their substrate, is used to process these cells into thin films. The advantages of single-crystal GaAs are thereby retained, while reducing weight and cutting cost by allowing for substrate reuse. Thin-film cells also have better thermal management capabilities and can be stacked for use in tandem structures. Cell fabrication and performance are described, and directions for further improvements are identified.

Dingle, B. D.↗
NASA NTRS1991

Decrease of summer tropospheric ozone concentrations in Antarctica

It is shown here that surface ozone concentrations at the South Pole in the austral summer decreased by 17 percent over the period 1976-90. Over the same period, solar irradiance at the South Pole in January and February decreased by 7 percent as a result of a 25 percent increase in cloudiness. It is suggested that the trend in the summer ozone concentrations is caused by enhanced photochemical destruction of ozone in the lower troposphere caused by the increased penetration of UV radiation associated with stratospheric ozone depletion, coupled with enhanced transport of ozone-poor marine air from lower latitudes to the South Pole.

Schnell, R. C.↗
NASA NTRS1991

On the seasonal phytoplankton concentration and sea surface temperature cycles of the Gulf of Mexico as determined by satellites

Multiyear series of coastal zone color scanner (CZCS) and AVHRR observations are presently used to derive monthly climatologies of near-surface phytoplankton pigment concentration and SST for the Gulf of Mexico; these, in combination with 1946-1987 SST data and NOAA hydrographic profile data covering 1914-1985, show that the most important single factor controlling seasonal cycle surface-pigment concentration is the depth of the mixed layer. The CZCS images indicate that seasonal variation seaward of the continental shelf is synchronous throughout the Gulf. The combination of ocean color and IR images allows year-round observation of surface circulation spatial structure in the Gulf, as well as of the dispersal pattern of the Mississippi River's plume.

Mueller-Karger, Frank E.↗
NASA NTRS1992

Modulating Concentration Of Hydrazine Vapor To Aid Detection

Three techniques, flow modulation, filament modulation, and reactive-filter modulation developed to obtain selective response to hydrazine or to methyl hydrazines from photoionization detector. Implemented in portable selective hydrazine detectors, useful where continuous or rapid, repetitive quantitative measurements of concentrations of vapors of these toxic substances required. Measure concentration of gaseous hydrazines in presence of other gases like cyclohexane, chlorofluorocarbons, and ammonia. Produce modulated signal, amplitude and phase indicating amount of hydrazine, monomethyl hydrazine, or 1,1-dimethyl hydrazine present in mixture. Used with such other detectors as electrochemical cells.

Stetter, Joseph R.↗
NASA NTRS1990

Atomic oxygen durability of solar concentrator materials for Space Station Freedom

The findings are reviewed of atomic oxygen exposure testing of candidate solar concentrator materials containing SiO2 and Al2O3 protective coatings for use on Space Station Freedom solar dynamic power modules. Both continuous and iterative atomic oxygen exposure tests were conducted. Iterative air plasma ashing resulted in larger specular reflectance decreases and solar absorptance increases than continuous ashing to the same fluence, and appears to provide a more severe environment than the continuous atomic oxygen exposure that would occur in the low Earth orbit environment. First generation concentrator fabrication techniques produced surface defects including scratches, macroscopic bumps, dendritic regions, porosity, haziness, and pin hole defects. Several of these defects appear to be preferential sites for atomic oxygen attack leading to erosive undercutting. Extensive undercutting and flaking of reflective and protective coatings were found to be promoted through an undercutting tearing propagation process. Atomic oxygen erosion processes and effects on optical performance is presented.

Degroh, Kim K.↗
NASA NTRS1992

Tracking performance with two breathing oxygen concentrations after high altitude rapid decompression

Current military aircraft Liquid Oxygen (LOX) systems supply 99.5 pct. gaseous Aviator's Breathing Oxygen (ABO) to aircrew. Newer Molecular Sieve Oxygen Generation Systems (MSOGS) supply breathing gas concentration of 93 to 95 pct. O2. The margin is compared of hypoxia protection afforded by ABO and MSOGS breathing gas after a 5 psi differential rapid decompression (RD) in a hypobaric research chamber. The barometric pressures equivalent to the altitudes of 46000, 52000, 56000, and 60000 ft were achieved from respective base altitudes in 1 to 1.5 s decompressions. During each exposure, subjects remained at the simulated peak altitude breathing either 100 or 94 pct. O2 with positive pressure for 60 s, followed by a rapid descent to 40000 ft. Subjects used the Tactical Life Support System (TLSS) for high altitude protection. Subcritical tracking task performance on the Performance Evaluation Device (PED) provided psychomotor test measures. Overall tracking task performance results showed no differences between the MSOGS breathing O2 concentration of 94 pct. and ABO. Significance RMS error differences were found between the ground level and base altitude trials compared to peak altitude trials. The high positive breathing pressures occurring at the peak altitudes explained the differences.

Nesthus, Thomas E.↗
NASA NTRS1992

In Vivo and in Vitro Chlorophyll-a and Pheophytin-a Concentration Measurements by Laser Fluorometry

Discussed here is the application of a laser fluorescent technique in in vivo and in vitro phyto- and zooplankton analysis involving popular lasers, an impulse YAG laser (lambda = 532 nm) and a steady state He-Cd (lambda = 440 nm). The YAG laser is widely used in laser remote sensing of seawater photoplankton in situ mode, but here we give special attention to its use in the precise estimation of phytoplankton pigments using laser induced fluorescence. The He-Cd laser is a novice in this field and, we believe, very promising. Our methods enable one to detect, in viro, chlorophyll-a (Chl-a) concentration in the water probe up to 10 nanograms per liter, and to measure, in vitro, Chl-a and pheophytin-a (Ph-a) concentrations in acetone extracts of phyto- and zooplankton up to 1 nanogram per liter.

Demidov, A. A.↗