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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 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

Forward Technology Solar Cell Experiment First On-Orbit Data

This paper presents first on orbit measured data from the Forward Technology Solar Cell Experiment (FTSCE). FTSCE is a space experiment housed within the 5th Materials on the International Space Station Experiment (MISSE-5). MISSE-5 was launched aboard the Shuttle return to flight mission (STS-114) on July 26, 2005 and deployed on the exterior of the International Space Station (ISS). The experiment will remain in orbit for nominally one year, after which it will be returned to Earth for post-flight testing and analysis. While on orbit, the experiment is designed to measure a 36 point current vs. voltage (IV) curve on each of the experimental solar cells, and the data is continuously telemetered to Earth. The experiment also measures the solar cell temperature and the orientation of the solar cells to the sun. A range of solar cell technologies are included in the experiment including state-of-the-art triple junction InGaP/GaAs/Ge solar cells from several vendors, thin film amorphous Si and CuIn(Ga)Se2 cells, and next-generation technologies like single-junction GaAs cells grown on Si wafers and metamorphic InGaP/InGaAs/Ge triple-junction cells. In addition to FTSCE, MISSE-5 also contains a Thin-Film Materials experiment. This is a passive experiment that will provide data on the effect of the space environment on more than 200 different materials. FTSCE was initially conceived in response to various on-orbit and ground test anomalies associated with space power systems. The Department of Defense (DoD) required a method of rapidly obtaining on orbit validation data for new space solar cell technologies, and NRL was tasked to devise an experiment to meet this requirement. Rapid access to space was provided by the MISSE Program which is a NASA Langley Research Center program. MISSE-5 is a completely self-contained experiment system with its own power generation and storage system and communications system. The communications system, referred to as PCSat, transmits and receives in the Amateur Radio band providing a node on the Amateur Radio Satellite Service. This paper presents an overview of the various aspects of MISSE-5 and a sample of the first measured on orbit data.

Walters, R. J.↗
NASA NTRS1985

Impurities in silicon solar cells

Metallic impurities, both singly and in combinations, affect the performance of silicon solar cells. Czochralski silicon web crystals were grown with controlled additions of secondary impurities. The primary electrical dopants were boron and phosphorus. The silicon test ingots were grown under controlled and carefully monitored conditions from high-purity charge and dopant material to minimize unintentional contamination. Following growth, each crystal was characterized by chemical, microstructural, electrical, and solar cell tests to provide a detailed and internally consistent description of the relationships between silicon impurity concentration and solar cell performance. Deep-level spectroscopy measurements were used to measure impurity concentrations at levels below the detectability of other techniques and to study thermally-induced changes in impurity activity. For the majority of contaminants, impurity-induced performance loss is due to a reduction of the base diffusion length. From these observations, a semi-empirical model which predicts cell performance as a function of metal impurity concentration was formulated. The model was then used successfully to predict the behavior of solar cells bearing as many as 11 different impurities.

Hopkins, R. H.↗
NASA NTRS1992

NASA Programs in Space Photovoltaics

Highlighted here are some of the current programs in advanced space solar cell and array development conducted by NASA in support of its future mission requirements. Recent developments are presented for a variety of solar cell types, including both single crystal and thin film cells. A brief description of an advanced concentrator array capable of AM0 efficiencies approaching 25 percent is also provided.

Flood, Dennis J.↗
NASA NTRS1996

Theories and models on the biological of cells in space

A wide variety of observations on cells in space, admittedly made under constraining and unnatural conditions in may cases, have led to experimental results that were surprising or unexpected. Reproducibility, freedom from artifacts, and plausibility must be considered in all cases, even when results are not surprising. The papers in symposium on 'Theories and Models on the Biology of Cells in Space' are dedicated to the subject of the plausibility of cellular responses to gravity -- inertial accelerations between 0 and 9.8 m/sq s and higher. The mechanical phenomena inside the cell, the gravitactic locomotion of single eukaryotic and prokaryotic cells, and the effects of inertial unloading on cellular physiology are addressed in theoretical and experimental studies.

Todd, P.↗
NASA NTRS2004

Evaluation of the Paratrend Multi-Analyte Sensor for Potential Utilization in Long-Duration Automated Cell Culture Monitoring

BACKGROUND: Compact and automated sensors are desired for assessing the health of cell cultures in biotechnology experiments. While several single-analyte sensors exist to measure culture health, a multi-analyte sensor would simplify the cell culture system. One such multi-analyte sensor, the Paratrend 7 manufactured by Diametrics Medical, consists of three optical fibers for measuring pH, dissolved carbon dioxide (pCO(2)), dissolved oxygen (pO(2)), and a thermocouple to measure temperature. The sensor bundle was designed for intra-vascular measurements in clinical settings, and can be used in bioreactors operated both on the ground and in NASA's Space Shuttle and International Space Station (ISS) experiments. METHODS: A Paratrend 7 sensor was placed at the outlet of a bioreactor inoculated with BHK-21 (baby hamster kidney) cells. The pH, pCO(2), pO(2), and temperature data were transferred continuously to an external computer. Cell culture medium, manually extracted from the bioreactor through a sampling port, was also assayed using a bench top blood gas analyzer (BGA). RESULTS: Two Paratrend 7 sensors were used over a single cell culture experiment (64 days). When compared to the manually obtained BGA samples, the sensor had good agreement for pH, pCO(2), and pO(2) with bias (and precision) 0.005(0.024), 8.0 mmHg (4.4 mmHg), and 11 mmHg (17 mmHg), respectively for the first two sensors. A third Paratrend sensor (operated for 141 days) had similar agreement (0.02+/-0.15 for pH, -4+/-8 mm Hg for pCO(2), and 24+/-18 mmHg for pO(2)). CONCLUSION: The resulting biases and precisions are com- parable to Paratrend sensor clinical results. Although the pO(2) differences may be acceptable for clinically relevant measurement ranges, the O(2) sensor in this bundle may not be reliable enough for the ranges of pO(2) in these cell culture studies without periodic calibration.

Validation Studies↗
NASA NTRS1983

Double layered tailorable advanced blanket insulation

An advanced flexible reusable surface insulation material for future space shuttle flights was investigated. A conventional fly shuttle loom with special modifications to weave an integral double layer triangular core fabric from quartz yarn was used. Two types of insulating material were inserted into the cells of the fabric, and a procedure to accomplish this was developed. The program is follow up of a program in which single layer rectangular cell core fabrics are woven and a single type of insulating material was inserted into the cells.

Falstrup, D.↗
NASA NTRS1988

Modeling and simulation of InP homojunction solar cells

Modeling and simulation of single-crystal InP homojunction solar cells has been performed using the PC-1D code. Cell design and performance have been optimized using the best available estimates of the various materials parameters. A comparison has been made of the predictions of the PC-1D model to those of other models. The optimum performance is predicted to give an efficiency approaching 21 percent at AM0. It is shown that in order to describe the performance of actual cells it is necessary to use larger values of the intrinsic carrier concentration and the surface recombination velocity (SRV) than have been reported in the literature. However, even with a near-maximum value of SRV (e.g., 10 to the 7th cm/s) it is necessary to reduce the minority carrier diffusion length in the emitter to only 0.01 micron in order to account for the relatively low quantum efficiency in the blue part of the spectrum. This indicates that improvement in the emitter bulk properties could be much more important than the SRV. Other loss mechanisms are also discussed; in particular, it is shown that recombination in the base, for good quality material, is relatively insignificant.

Yahia, A. H.↗
NASA NTRS1989

Ultra-thin, light-trapping silicon solar cells

Design concepts for ultra-thin (2 to 10 microns) high efficiency single-crystal silicon cells are discussed. Light trapping allows more light to be absorbed at a given thickness, or allows thinner cells of a given Jsc. Extremely thin cells require low surface recombination velocity at both surfaces, including the ohmic contacts. Reduction of surface recombination by growth of heterojunctions of ZnS and GaP on Si has been demonstrated. The effects of these improvements on AM0 efficiency is shown. The peak efficiency increases, and the optimum thickness decreases. Cells under 10 microns thickness can retain almost optimum power. The increase of absorptance due to light trapping is considered. This is not a problem if the light-trapping cells are sufficiently thin. Ultra-thin cells have high radiation tolerance. A 2 microns thick light-trapping cell remains over 18 percent efficient after the equivalent of 20 years in geosynchronous orbit. Including a 50 microns thick coverglass, the thin cells had specific power after irradiation over ten times higher than the baseline design.

Landis, Geoffrey A.↗
NASA NTRS1991

Performance of a Dual Anode Nickel-Hydrogen Cell

Nickel-hydrogen batteries are presently being used for energy storage on satellites in low Earth orbit and in geosynchronous orbit, and have also been selected for use on the proposed Space Station Freedom. Development continues on the cell technology in order to improve the specific energy and lengthen the cycle life. An experimental study was conducted to compare the voltage performance of a nickel-hydrogen cell containing a dual anode with the standard cell design which uses a single hydrogen electrode. Since the principle voltage loss in a nickel-hydrogen cell is attributed to the mass transport and resistive polarization parameters of the nickel electrode, addition of a hydrogen electrode on the other side of the nickel electrode should reduce the electrochemical polarizations by a factor of two. A 3.5 in. diameter boilerplate cell with a single 30 mils thick nickel electrode was cycled under various current conditions to evaluate its performance with a single anode and then with a double anode. A layered separator consisting of one Zircar cloth separator and one radiation-grafted polyethylene separator were used between the electrodes. The electrolyte was 26% KOH, and the tests were done at room temperature. The discharge voltage characteristics were determined as a function of current and depth-of-discharge. At the 4C discharge rate and 50% DOD, the voltage of the dual anode cell was 100 mV higher than the single anode cell. At 75% DOD the dual anode cell voltage was about 130 mV higher than the standard cell design. Resistances of the two c ell designs obtained from the slope of the mid-discharge voltages plotted against various currents indicated that the dual anode cell resistance was one-half of the state-of-the-art cell.

Gahn, Randall F.↗
NASA NTRS1977

Improved fuel cell

Concept in fuel cell design has two cells, each with its own reactant flow fields bonded into single modular unit. Cells require fewer parts and occupy less space than conventional fuel cells, effecting easier assembly and maintenance.

Bell, W. F.↗
NASA NTRS1971

Photoemf in cadmium sulfide

Theoretical and experimental investigations on CdS single crystals and CuxS:CdS photovoltaic cells prepared from CdS single crystals by a chemical-dip procedure are described. The studies are aimed at clarifying cell mechanisms which affect key cell properties (efficiency, reliability, and lifetime) by examining the properties of intrinsic and extrinsic defects in the junction and surface regions and their effects on carrier transport through these regions. The experimental research described includes studies of thermal, infrared, and field quenching of acceptor-doped CdS crystals; investigation of optical and electrical properties of CuxS:CdS photovoltaic cells (current-voltage characteristics, spectral distribution of photocurrent and photovoltage) and the dependence of these properties on temperature and light intensity; measurement of changes, as a result of heat treatment in ultrahigh vacuum, in the spectral distribution of photoconductivity at room temperature and liquid nitrogen temperature, the luminescence spectrum at liquid nitrogen temperature, and the thermally stimulated current curves of CdS crystals; determination of the effect of irradiation with 150 keV (maximum) X-rays on the spectral distribution of photoconductivity and thermally-stimulated current of CdS crystals; and studies of the effect of growth conditions on the photoconductive properties of CdS crystals.

Boeer, K. W.↗
NASA NTRS1986

Point contact silicon solar cells

The construction of a 22.2% efficient single-crystal silicon solar cell fabricated at Stanford University is described. The cell dimensions were 3 x 5 mm and 100 microns thick with a base lifetime of 500 microseconds. The cell featured light trapping between a texturized top surface and a reflective bottom surface, small point contact diffusions, alternating between n-type and p-type in a polka-dot pattern on the bottom surface, and a surface passivation on all surfaces between contact regions.

Swanson, R. M.↗
NASA NTRS1991

Free stream capturing in fluid conservation law for moving coordinates in three dimensions

The free-stream capturing technique for both the finite-volume (FV) and finite-difference (FD) framework is summarized. For an arbitrary motion of the grid, the FV analysis shows that volumes swept by all six surfaces of the cell have to be computed correctly. This means that the free-stream capturing time-metric terms should be calculated not only from a surface vector of a cell at a single time level, but also from a volume swept by the cell surface in space and time. The FV free-stream capturing formulation is applicable to the FD formulation by proper translation from an FV cell to an FD mesh.

Obayashi, Shigeru↗
NASA NTRS2009

Quantum-Well Thermophotovoltaic Cells

Thermophotovoltaic cells containing multiple quantum wells have been invented as improved means of conversion of thermal to electrical energy. The semiconductor bandgaps of the quantum wells can be tailored to be narrower than those of prior thermophotovoltaic cells, thereby enabling the cells to convert energy from longer-wavelength photons that dominate the infrared-rich spectra of typical thermal sources with which these cells would be used. Moreover, in comparison with a conventional single-junction thermophotovoltaic cell, a cell containing multiple narrow-bandgap quantum wells according to the invention can convert energy from a wider range of wavelengths. Hence, the invention increases the achievable thermal-to-electrical energy-conversion efficiency. These thermophotovoltaic cells are expected to be especially useful for extracting electrical energy from combustion, waste-heat, and nuclear sources having temperatures in the approximate range from 1,000 to 1,500 C.

Freudlich, Alex↗
NASA NTRS1999

Genetic Regulation of Charged Particle Mutagenesis in Human Cells

Our studies use a series of syngeneic, and where possible, isogenic human B-lymphoblastoid cell lines to assess the genetic factors that modulate susceptibility apoptosis and their impact on the mutagenic risks of low fluence exposures to 1 GeV Fe ions and 55 MeV protons. These ions are representative of the types of charged particle radiation that are of particular significance for human health in the space radiation environment. The model system employs cell lines derived from the male donor WIL-2. These cells have a single X chromosome and they are hemizygous for one mutation marker, hypoxanthine phosphoribosyltransferase (HPRT). TK6 and WTK1 cells were each derived from descendants of WIL-2 and were each selected as heterozygotes for a second mutation marker, the thymidine kinase (TK) gene located on chromosome 17q. The HPRT and TK loci can detect many different types of mutations, from single basepair substitutions up to large scale loss of heterozygosity (LOH). The single expressing copy of TK in the TK6 and WTKI cell lines is found on the same copy of chromosome 17, and this allele can be identified by a restriction fragment length polymorphism (RFLP) identified when high molecular weight DNA is digested by the SacI restriction endonuclease and hybridized against the cDNA probe for TK. A large series of polymorphic linked markers has been identified that span more than 60 cM of DNA (approx. 60 megabasepairs) and distinguish the copy of chromosome 17 bearing the initially active TK allele from the copy of chromosome 17 bearing the silent TK allele in both TK6 and WTKI cells. TK6 cells express normal p53 protein while WTKI cells express homozygous mutant p53. Expression of mutant p53 can increase susceptibility to x-ray-induced mutations. It's been suggested that the increased mutagenesis in p53 mutant cells might be due to reduced apoptosis.

Kronenberg, Amy↗
NASA NTRS2005

High Quality GaAs Growth by MBE on Si Using GeSi Buffers and Prospects for Space Photovoltaics

III-V solar cells on Si substrates are of interest for space photovoltaics since this would combine high performance space cells with a strong, lightweight and inexpensive substrate. However, the primary obstacles blocking III-V/Si cells from achieving high performance to date have been fundamental materials incompatabilities, namely the 4% lattice mismatch between GaAs and Si, and the large mismatch in thermal expansion coefficient. In this paper, we report on the molecular beam epitaxial (MBE) growth and properties of GaAs layers and single junction GaAs cells on Si wafers which utilize compositionally graded GeSi Intermediate buffers grown by ultra-high vacuum chemical vapor deposition (UHVCVD) to mitigate the large lattice mismatch between GaAs and Si. Ga As cell structures were found to incorporate a threading dislocation density of 0.9-1.5 x 10 (exp 6) per square centimeter, identical to the underlying relaxed Ge cap of the graded buffer, via a combination of transmission electron microscopy, electron beam induced current, and etch pit density measurements. AlGaAs/GaAs double heterostructures wre grown on the GeSi/Si substrates for time-resolved photoluminescence measurements, which revealed a bulk GaAs minority carrier lifetime in excess of 10 ns, the highest lifetime ever reported for GaAs on Si. A series of growth were performed to ass3ss the impact of a GaAs buffer to a thickness of only 0.1 micrometer. Secondary ion mass spectroscopy studies revealed that there is negligible cross diffusion of Ga, As and Ge at he III-V/Ge interface, identical to our earlier findings for GaAs grown on Ge wafers using MBE. This indicates that there is no need for a buffer to "bury" regions of high autodopjing,a nd that either pn or np configuration cells are easily accomodated by these substrates. Preliminary diodes and single junction Al Ga As heteroface cells were grown and fabricated on the Ge/GeSi/Si substrates for the first time. Diodes fabricated on GaAs, Ge and Ge/GeSi/Si substrate show nearly identical I-V characteristics in both forward and reverse bias regions. External quantum efficiencies of AlGaAs/GaAs cell structures grown on Ge/GeSi/Si and Ge substrates demonstrated nearly identical photoresponse, which indicates that high lifetimes, diffusion lengths and efficient minority carrier collection is maintained after complete cell processing.

Carlin, J. A.↗
NASA NTRS2002

Single Source Precursors for Thin Film Solar Cells

The development of thin film solar cells on flexible, lightweight, space-qualified substrates provides an attractive cost solution to fabricating solar arrays with high specific power, (W/kg). The use of a polycrystalline chalcopyrite absorber layer for thin film solar cells is considered as the next generation photovoltaic devices. At NASA GRC we have focused on the development of new single source precursors (SSP) and their utility to deposit the chalcopyrite semi-conducting layer (CIS) onto flexible substrates for solar cell fabrication. The syntheses and thermal modulation of SSPs via molecular engineering is described. Thin-film fabrication studies demonstrate the SSPs can be used in a spray CVD (chemical vapor deposition) process, for depositing CIS at reduced temperatures, which display good electrical properties, suitable for PV (photovoltaic) devices.

Banger, Kulbinder K.↗