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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 757 records · Page 42
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Helium resources of Mare Tranquillitatis

Wisconsin Center for Space Automation and Robotics, Univ. of Wisc., Madison, Wisc. Mare Tranquillitatis, about 300000 sq km in area, is currently the most promising lunar source of He-3 for fueling fusion power plants on Earth. About 60 pct. of the mare regolith consists of particles 100 microns or less in diameter. Helium and other gases derived from the solar wind are concentrated in the fine size fractions. Studies of very small craters indicate that the average regolith exceeds 3 m in areas away from larger craters and other mare features not amenable to mining. There is no evidence of decrease of helium content of regolith and depth. Helium is known to be enriched in regoliths that are high in TiO2 content. Remote sensing indicates that about 90 pct. of Mare Tranquillitatis is covered by regolith ranging from about 6 to +7.5 pct. TiO2; inferred He contents range from 20 to at least 45 wppm total helium (7 to 18 wppb He-3). Detailed studies of craters and inferred ejecta halos displayed on high resolution photographs of the Apollo 11 and Ranger 8 areas suggest that as much as 50 pct. of the mare regolith may be physically minable, on average, with appropriate mining equipment. Assuming that the average thickness of regolith is 3 m, and that 50 pct. of the mare area is minable, the He-3 content of minable regolith containing 20 to 45 wppm total He is estimated at about 94,000 tonnes.

Cameron, Eugene N.↗
NASA NTRS1991

Siphon flows in isolated magnetic flux tubes. IV - Critical flows with standing tube shocks

Critical siphon flows in arched, isolated magnetic flux tubes are studied within the thin flux tube approximation, with a view toward applications to intense magnetic flux concentrations in the solar photosphere. The results of calculations of the strength and position of the standing tube shock in the supercritical downstream branch of a critical siphon flow are presented, as are calculations of the flow variables all along the flux tube and the equilibrium path of the flux tube in the surrounding atmosphere. It is suggested that arched magnetic flux tubes, with magnetic field strength increased by a siphon flow, may be associated with some of the intense, discrete magnetic elements observed in the solar photosphere.

Thomas, John H.↗
NASA NTRS2002

Power Without Wires (POWOW)

Electric propulsion has emerged as a cost-effective solution to a wide range of satellite applications. Deep Space 1 successfully demonstrated electric propulsion as the primary propulsion source for a satellite. The POWOW concept is a solar-electric propelled spacecraft capable of significant cargo and short trip times for traveling to Mars. There it would enter areosynchronous orbit (Mars GEO equivalent) and beam power to surface installations via lasers. The concept has been developed with industrial partner expertise in high efficiency solar cells, advanced concentrator modules, innovative arrays, and high power electric propulsion systems. The present baseline spacecraft design providing 898 kW using technologies expected to be available in 2003 will be described. Areal power densities approaching 350 W/sq m at 80 C operating temperatures and wing level specific powers of over 350 W/kg are projected. Details of trip times and payloads to Mars are presented. Electric propulsion options include Hall, MPD, and ion thrusters of various power levels and trade studies have been conducted to define the most advantageous options. Because the design is modular, learning curve methodology has been applied to determine expected cost reductions and is included.

Brandhorst, Henry W., Jr.↗
NASA NTRS1999

Space Solar Power: Satellite Concepts

Space Solar Power (SSP) applies broadly to the use of solar power for space related applications. The thrust of the NASA SSP initiative is to develop concepts and demonstrate technology for applying space solar power to NASA missions. Providing power from satellites in space via wireless transmission to a receiving station either on earth, another celestial body or a second satellite is one goal of the SSP initiative. The sandwich design is a satellite design in which the microwave transmitting array is the front face of a thin disk and the back of the disk is populated with solar cells, with the microwave electronics in between. The transmitter remains aimed at the earth in geostationary orbit while a system of mirrors directs sunlight to the photovoltaic cells, regardless of the satellite's orientation to the sun. The primary advantage of the sandwich design is it eliminates the need for a massive and complex electric power management and distribution system for the satellite. However, it requires a complex system for focusing sunlight onto the photovoltaic cells. In addition, positioning the photovoltaic array directly behind the transmitting array power conversion electronics will create a thermal management challenge. This project focused on developing designs and finding emerging technology to meet the challenges of solar tracking, a concentrating mirror system including materials and coatings, improved photovoltaic materials and thermal management.

Little, Frank E.↗
NASA NTRS2006

High Power, High Voltage Electric Power System for Electric Propulsion

This paper provides an overview of the 30 KW, 600 V MRHE power subsystem. Descriptions of the power subsystem elements, the mode of power transfer, and power and mass estimates are presented. A direct-drive architecture for electric propulsion is considered which reduces mass and complexity. Solar arrays with concentrators are used for increased efficiency. Finally, the challenges due to the environment of a hypothetical lunar mission as well as due to the advanced technologies considered are outlined.

direct drives↗
NASA NTRS1982

Determination of optimum sunlight concentration level in space for 3-5 cascade solar cells

Current-voltage curves were calculated for each cell in a cascade structure using a solar cell diode equation and superposition. Terms for the light generated current, diffusion current, space charge recombination current and series and shunt resistance are included. Individual current voltage curves are added in series with ohmic resistance losses for the cell interconnects to obtain the cascade cell performance. Temperature was varied with concentration, using several models, and ranged from 55 C at one Sun to between 80 and 200 C at 100 Suns. A variety of series resistance and internal resistances were used. Coefficients of the diffusion and recombination terms are strongly temperature dependent. The study indicates that maximum efficiency (30%) occurs in the 50 to 100X Sun concentration range, provided series resistance is below 0.015 ohm-sq cm and cell temperature is 80 C at 100 Suns.

Curtis, H. B.↗
NASA NTRS1985

Performance of Hughes GaAs concentrator cells under 1-MeV electron irradiation

Several Hughes gallium arsenide (GaAs) concentrator cells were exposed to 1-MeV electrons at fluences up to 1x10 to the 15th power electrons/sq cm. Performance data were taken after several fluences, at two temperatures, and at concentration levels from 1 to approx. 150x AMO. Data at 1 sun and 25 deg C were taken with an X-25 xenon-lamp solar simulator. Data at concentration were taken using a pulsed solar simulator with the assumption of a linear relationship between short-circuit current and irradiance. The cells are 5 by 5 mm with a 4-mm diameter illuminated area.

Curtis, H. B.↗
NASA NTRS1979

A theoretical study of heterojunction and graded band gap type solar cells

The work performed concentrated on including multisun effects, high temperature effects, and electron irradiation effects into the computer analysis program for heterojunction and graded bandgap solar cells. These objectives were accomplished and the program is now available for such calculations.

Chiang, J. P. C.↗
NASA NTRS1981

Modulation of Venus ion densities associated with solar variations

The dayside ion concentrations in the Venus ionosphere obtained by the Pioneer Venus orbiter ion mass spectrometer exhibit a modulation corresponding to the 27-day solar variation. Comparisons were made of the amplitudes of modulation of CO(2(+), C(+), and O2(+), with the amplitudes of the 27-day variation in the 10.7-cm solar radio flux and the simultaneously measured EUV fluxes at He II (304 A) and Lyman-beta(1026 A), together with a theoretical analysis of the effects of solar variability on the ionosphere and neutral atmosphere of Venus. This analysis leads to the conclusion that the observed modulation of dayside ion densities is primarily due to the variability in the ionizing EUV radiations and, to a much lesser extent, the result of the variability with solar activity of the neutral atmosphere via the variability in exospheric temperature. In this connection, it is also shown theoretically why the percentage variation of exospheric temperature on Venus (as observed in the ONMS data) for a given variation in the 10.7-cm radio flux is only half of the exospheric temperature variation for earth.

Bauer, S. J.↗
NASA NTRS1980

Analysis of GaAs and Si solar cell arrays for earth orbital and orbit transfer missions

Solar array systems have been studied and compared for earth orbital and orbit transfer missions with the principal objective of quantifying the cost tradeoffs between gallium arsenide and silicon array for specific classes of missions and system characteristics. For the missions considered, it is found that the purchase cost advantage of Si arrays is not overcome by the greater radiation resistance of GaAs arrays. The use of reflectors for concentration may significantly reduce the power system cost. However, GaAs arrays benefit considerably more from solar concentration than Si arrays in terms of mission cost because of their higher allowable temperature. In the case of orbit transfer missions, a cover glass thickness of at least 0.05 cm is recommended to reduce total mission cost.

Jefferies, K. S.↗
NASA NTRS1978

Pressure sensing of the atmosphere by solar occultation - An application to remote sensing of atmospheric minor gases

The simultaneous inference of pressure and gas concentration in a remote-sensing experiment will increase the accuracy of inverted gas concentrations and minimize the dependence of the experiment on pressure or mass-path error resulting from use of climatological pressure data, satellite ephemeris, and instrument pointing accuracy. A technique for obtaining tangent-point pressure information needed for inversion of gas concentration in an IR solar occultation experiment is described. By measuring IR absorption in bands of atmospheric CO2 (e.g., 2.0, 2.7, or 4.3 microns) pressure values for each layer (2 km or less in the vertical) of the atmosphere can be obtained with rms errors of less than 3%.

Park, J. H.↗
NASA NTRS1977

Impurity concentrations and surface charge densities on the heavily doped face of a silicon solar cell

Increased solar cell efficiencies are attained by reduction of surface recombination and variation of impurity concentration profiles at the n(+) surface of silicon solar cells. Diagnostic techniques are employed to evaluate the effects of specific materials preparation methodologies on surface and near surface concentrations. It is demonstrated that the MOS C-V method, when combined with a bulk measurement technique, yields more complete concentration data than are obtainable by either method alone. Specifically, new solar cell MOS C-V measurements are combined with bulk concentrations obtained by a successive layer removal technique utilizing measurements of sheet resistivity and Hall coefficient.

Weinberg, I.↗
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 NTRS1976

A fixed collector employing reversible vee-trough concentrator and a vacuum tube receiver for high temperature solar energy systems

A solar heat collection system employing non-tracking reflectors integrated with a fixed vacuum tube receiver which achieves modest year-round concentration (about 2) of the sunlight at low capital costs is discussed. The axis of the vee-trough reflector lies in a east-west direction and requires reversal of the reflector surfaces only twice a year without disturbing the receiver tubes and associated plumbing. It collects most of the diffuse flux. The vacuum tube receiver with selective absorber has no convection losses while radiation and conduction losses are minimal. Significant cost reductions are offered since the vee-trough can be fabricated from inexpensive polished or plastic reflector laminated sheet metal covering 2/3 of the collection area, and only about 1/3 of the area is covered with the more expensive vacuum tube receivers. Thermal and economic performance of the vee-trough vacuum tube system, year-round variation of the concentration factor, incident flux, useful heat per unit area at various operation temperatures and energy cost estimates are presented. The electrical energy cost is estimated to be 77 mills/kWh, and the system construction cost is estimated to be $1140/kWe.

Selcuk, M. K.↗
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 (CFC-22), and COF2 in the lower stratosphere have been derived from analysis of ca. 1980 and more recent infrared solar occultation spectra recorded near 32 deg N latitude at approx. 0.02/ cm resolution. Consistent sets of line parameters and spectral calibration methods have been used in the retrievals to minimize systematic error effects. Quoted error limits are 1 sigma estimated precisions. The SF6 and CHClF2 results are based on spectra recorded by balloon-borne interferometers in March 1981 and June 1988 and a comparison of these results with the Atmospheric Trace Molecule Spectroscopy (ATMOS) Experiment/Spacelab 3 measurements obtained in May 1985 near 30 deg N latitude. In the 13-18 km altitude range the mean measured SF6 mixing ratio in parts per trillion by volume (pptv) increased from 1.17 +/- 0.21 in March 1981 to 2.02 +/- 0.20 pptv in June 1988, and the CHClF2 mixing ratio below 15 km altitude increased from 51 +/- 8 pptv in March 1981 to 102 +/- 10 pptv in June 1988. The CHClF2 retrievals used new empirical CHClF2 line parameters derived from 0.03/cm resolution laboratory spectra recorded at six temperatures between 203 and 293 K; the derived mixing ratios are approx. 30% higher than obtained with earlier sets of line parameters, thereby removing a large discrepancy noted previously between IR and in situ measurements of CHClF2. Assuming an exponential growth model for fitting the trends, SF6 and CHClF2 mean increase rates of 7.4% +/- 1.9% and 9.4% +/- 1.3% /year, are obtained, respectively, which correspond to cumulative increases by factors of approx. 1.7 and -2.0 in the concentrations of these gases over the 7.2-year measurement period. Analysis of spectra recorded in October 1979 and April 1989 yields COF2 volume mixing ratios that are respectively 0.44 +/- 0.17 and 1.21 +/- 0.24 times the ATMOS/Spacelab 3 values, from which an average COF2 increase rate of 10.3 +/- 1.8%/ year over this time period has been estimated. The present results are compared with previously reported observations and trends and with one-dimensional model calculations. The model calculated trends are in reasonably good agreement with the observations.

Rinsland, C. P.↗
NASA NTRS1978

Evidence for the existence of Pd-107 in the early solar system

Measurements of the concentration and isotopic composition of Ag and Pd in the Santa Clara iron meteorite suggest that in situ decay of Pd-107 occurred in the meteorite or its parent body. The initial solar ratio of Pd-107/Pd-110 is estimated from the observed ratio of excess Ag-107/Pd-110, and the value of the Pd ratio is incompatible with an interval of approximately 100,000,000 years between the end of nucleosynthesis and the formation of planetary objects but is compatible with a later injection of material. The inferred existence of Pd-107 and Al-26 indicates that the late injection included freshly synthesized material of both intermediate and low atomic weight on a similar time scale. The significance of the Pd-107/Ag-107 chronometer is considered.

Kelly, W. R.↗
NASA NTRS1995

Competition of supermassive black holes and galactic spheroids in the destruction of globular clusters

The globular clusters that we observe in galaxies may be only a fraction of the initial population. Among the evolutionary influences on the population is the destruction of globular clusters by tidal forces as the cluster moves through the field of influence of a disk, a bulge, and/or a putative nuclear component (black hole). We have conducted a series of N-body simulations of globular clusters on bound and marginally bound orbits through poetentials that include black hole and speroidal components. The degree of concentration of the spheroidal component can have a considerable impact on the extent to which a globular cluster is disrupted. If half the mass of a 10(exp 10) solar mass spheroid is concentrated within 800 pc, then only black holes with masses greater than 10(exp 9) solar mass can have a significant tidal influence over that already exerted by the bulge. However, if the matter in the spheroidal component is not so strongly concentrated toward the center of the galaxy, a more modest central black hole (down to 10(exp 8) solar mass) could have a dominant influence on the globular cluster distribution, particularly if many of the clusters were initially on highly radial orbits. Our simulations show that the stars that are stripped from a globular cluster follow orbits with roughly the same eccentricity as the initial cluster orbit, spreading out along the orbit like a 'string of pearls.' Since only clusters on close to radial orbits will suffer substantial disruption, the population of stripped stars will be on orbits of high eccentricity.

Charlton, Jane C.↗