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At least 721 records · Page 40

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NASA NTRS1992

Synoptic maps of heliospheric Thomson scattering brightness from 1974-1985 as observed by the Helios photometers

We display the electron Thomson scattering intensity of the inner heliosphere as observed by the zodiacal light photometers on board the Helios spacecraft in the form of synoptic maps. The technique extrapolates the brightness information from each photometer sector near the Sun and constructs a latitude/longitude map at a given solar height. These data are unique in that they give a determination of heliospheric structures out of the ecliptic above the primary region of solar wind acceleration. The spatial extent of bright, co-rotating heliospheric structures is readily observed in the data north and south of the ecliptic plane where the Helios photometer coverage is most complete. Because the technique has been used on the complete Helios data set from 1974 to 1985, we observe the change in our synoptic maps with solar cycle. Bright structures are concentrated near the heliospheric equator at solar minimum, while at solar maximum bright structures are found at far higher heliographic latitudes. A comparison of these maps with other forms of synoptic data are shown for two available intervals.

Hick, P.↗

NASA NTRS2008

A Solar-Powered Enceladus Mission

We present the results of a concept design study for a New Frontiers or small Flagship-class mission to Enceladus, using solar power. By concentrating on the science objectives most critical for a Cassini follow-on, this mission maximizes the science return while maintaining a power consumption level that can be provided by a practical solar power system. The optimized instrument payload is the product of a broad science community-based Science Definition Team Study. The spacecraft and mission designs are the products of studies carried out by the GSFC Mission Design Lab and Ball Aerospace. In addition to the low isolation at Enceladus, its location deep in Saturn's gravity well makes it a challenging target to reach, meaning that careful consideration must be given to spacecraft mass and the potential mission types. This presentation summarizes the mission science objectives and payload, the dynamical work, and the notional operations plan of this mission.

Simon-Miller, Amy A.↗

NASA NTRS1982

Development status of the small community solar power system

The development status and test results for the Small Community Solar Thermal Power Experiment are presented. Activities on the phase 2 power module development effort are presented with emphasis on the receiver, the plant control subsystem, and the energy transport subsystem. The components include a single prototype power module consisting of a parabolic dish concentrator, a power conversion assembly (PCA), and a multiple-module plant control subsystem. The PCA consists of a cavity receiver coupled to an organic Rankine cycle engine-alternator unit defined as the power conversion subsystem; the PCA is mounted at the focus of a parabolic dish concentrator. At a solar insolation of 100 W/sq m and ambient temperature of 28 C (82 F), the power module produces approximately 20 kW of 3-phase, 3 kHz ac power, depending on the concentrator employed. A ground-mounted rectifier to the central collection site where it is supplied directly to the common dc bus which collects the power from all modules in the plant.

Pons, R. L.↗

NASA NTRS1975

Solar-wind and solar-flare maturation of the lunar regolith

Detailed predictions concerning the depth and time-dependent accumulation of solar-wind effects and solar-flare tracks in lunar dust grains were obtained by use of an adaptation of a Monte Carlo soil-mixing computer code described by Duraud et al. (1975). The predictions are compared to experimental measurements obtained by analyzing lunar dust grains as well as artificially irradiated minerals by a variety of techniques. A study of amorphous coatings of solar-wind radiation-damaged material on certain lunar grains sets limits on the integrated residence time of these grains in the ancient solar wind. Other topics discussed include solar wind maturation, the peculiar shape of the experimental distribution of central track densities in 50-micron grains, and the interpretation of both track gradients in 50-micron feldspars and the relatively 'low' concentration of solar-wind species implanted in ilmenite grains.

Bibring, J. P.↗

NASA NTRS1977

Solar energy collection system

An improved solar energy collection system, having enhanced energy collection and conversion capabilities, is delineated. The system is characterized by a plurality of receivers suspended above a heliostat field comprising a multiplicity of reflector surfaces, each being adapted to direct a concentrated beam of solar energy to illuminate a target surface for a given receiver. A magnitude of efficiency, suitable for effectively competing with systems employed in collecting and converting energy extracted from fossil fuels, is indicated.

Selcuk, M. K.↗

NASA NTRS1981

Observations of solar-wind helium

It is pointed out that the concentration of helium in the solar wind relative to hydrogen fluctuates wildly. Under certain circumstances, the helium to hydrogen abundance ratio is strongly enhanced over probable solar values; at other times, the amount of helium in the solar wind is immeasurably small. In spite of the fact that helium is heavier than hydrogen, solar-wind helium often leaves the solar gravitational field with a higher velocity than does the hydrogen. It is thought that the mechanisms responsible for helium behavior may contain clues to unanswered questions concerning the acceleration and energy exchange processes of the entire solar wind. A brief review is given of the principal features and theories of the solar wind as a whole. In addition, measurement techniques are discussed. Emphasis throughout is on the experimental data concerning the dynamics of solar-wind helium. On the basis of coronal temperatures, it is shown that helium in the solar wind is almost always doubly ionized. It is also shown that the average abundance of helium ions in the solar wind is usually in the range of 3 to 6% by number.

Neugebauer, M.↗

NASA NTRS1984

Prebiotic syntheses of purines and pyrimidines

The results of experimental and theoretical investigations of the prebiotic synthesis of purines and pyramidines are surveyed. Topics examined include the synthesis of purines from HCN via 4,5-disubstituted imidazole derivatives in aqueous solutions or liquid NH3, simultaneous formation of amino acids and purines by electron irradiation of CH4-NH3-H2O mixtures, synthesis of pyrimadines from cynoacetylene, energetics, formation of bases under anhydrous or concentrated conditions, formation of bases under dilute conditions, Fischer-Tropsch-type reactions, and the role of activated intermediates. It is pointed out that the precursor compounds have been detected in the interstellar medium, on Titan, and in other solar-system bodies, and that solar-nebula HCN concentrations of the order of 1-10 mM have been estimated on the basis of meteorite measurements.

Basile, B.↗

NASA NTRS2000

POwer WithOut Wire (POWOW): A SEP Concept for Space Exploration

Electric propulsion has emerged as a cost-effective solution to a wide range of satellite applications. Deep Space 1 demonstrated electric propulsion as a primary propulsion source for a spacecraft. The POwer WithOut Wires (POWOW) concept has been developed as a solar electric propelled spacecraft that would travel to Mars, for example, enter selenosynchronous orbit and then use lasers to beam power to surface installations. This concept has been developed with industrial expertise in high efficiency solar cells, advanced concentrator modules, innovative arrays, and high power electric propulsion systems. The paper will present the latest version of the spacecraft, the technologies involved, possible missions and trip times to Mars and laser beaming options. The POWOW spacecraft is a general purpose solar electric propulsion system that includes technologies that are directly applicable to commercial and government spacecraft with power levels ranging from 4 kW in Low Earth Orbits (LEO) to about 1 MW. The system is modular and expandable. Learning curve costing methodologies are used to demonstrate cost effectiveness of a modular system.

Brandhorst, Henry W., Jr.↗

NASA NTRS1975

Application of the MOS-C-V technique to determine impurity concentrations and surface parameters on the diffused face of silicon solar cells

The feasibility of using the MOS C-V technique to obtain information regarding impurity and surface state concentrations on the diffused face of silicon solar cells with Ta2O5 coatings is studied. Results indicate that the MOS C-V technique yields useful information concerning surface parameters which contribute to the high, efficiency limiting, surface recombination velocities on the n+ surface of silicon solar cells.

Weinberg, I.↗

NASA NTRS1979

Thermal power systems point-focusing distributed receiver technology project. Volume 1: Executive summary

Thermal or electrical power from the sun's radiated energy through Point-Focusing Distributed Receiver Technology is the goal of this project. The energy thus produced must be technically, as well as economically, competitive with other energy sources. This project is to support the industrial development of the required technology to achieve the above stated goal. Solar energy is concentrated by either a reflecting surface or a lense to a receiver where it is transferred to a working liquid or gas. Receiver temperatures are in the 1000 - 2000 F range. Conceptual design studies are expected to identify power conversion units with a viable place in the solar energy future. Rankine and Brayton cycle engines are under investigation. This report details the Jet Propulsion Laboratory's accomplishments with point-focusing technology in Fy 1978.

Lucas, J.↗

NASA NTRS1999

Optical Evaluation of a Refractive Secondary Concentrator

Refractive secondary concentrators are being considered for solar thermal applications because of their ability to archive maximum efficiency through the use of total internal reflection for the concentration and distribution of solar energy. A prototype refractive secondary concentrator was built based on ray tracing analysis to demonstrate this collection and distribution concept. The design included a conical secondary concentrator and a faceted extractor. The objective of this effort was to functionally evaluate the performance of the refractive secondary concentrator/extractor prototype and to compare the results with modeling. Most of the light was found to exit the refractive secondary concentrator through the extractor. In addition, the degree of attenuation encountered by the light as it passed through the refractive secondary concentrator was of interest. Quantifying optical output and validating the modeling will provide further understanding of the efficiency of the prototype and will provide insight for additional design and materials selection activities.

Jaworske, Donald A.↗

NASA NTRS1980

Concentrator-enhanced photovoltaic arrays for deep space applications

The useful operational range of photovoltaic solar arrays has been limited to 1.5 AU (Mars orbit) due primarily to solar intensity constraints. Preliminary results indicate that the use of concentrator mirrors in conjunction with solar arrays can extend the practical operating range of photovoltaic space power sources to at least 9.5 AU (Saturn orbit). Various aspects of concentrator-enhanced photovoltaic arrays such as size, structure, thermal characteristics, intensity uniformity, pointing accuracy requirements, deployment methods, power performance and system mass are presented. Based on this information, concentrator-enhanced photovoltaic arrays are superior, with respect to power-to-mass and cost, to existing power sources used for deep space missions. The sensitivity of concentrator-enhanced solar arrays to particulate radiation was also examined for representative deep space missions. Results are presented which show that a radiation-degraded, deep space, concentrator-enhanced solar array's performance exceeds that of existing RTG power sources.

Rockey, D. E.↗

NASA NTRS2004

High-Order Simulation of Non-Linear Oscillations and Shocks in the Solar Atmosphere

The solar atmosphere presents a rich source of highly non-linear magneto-hydrodynamic phenomena: strong gradients and forcing terms result in both large shocks and oscillations. The additional requirements of energy balance and initialization in hydrostatic equilibrium compound the challenge of this problem. A wealth of observational data allows us to check the results of our simulations. The problem of simulating the solar atmosphere provides, in addition to an interesting system in its own right, a challenging testbed for high-order shock-capturing methods. We discuss the challenge of simulating solar atmospheric phenomena, concentrating on various high-order central methods ranging from second to fourth order. Our method is based on the central-upwind scheme of Kurganov, Noelle and Petrova, which we extend to high order via various interpolants. We investigate various initial data for our simulations, corresponding to observed conditions in different regions of the solar surface: the normal quiet sun and sunspots. When non-oscillatory using second- and third-order methods, we are able to reproduce non-trivial observational results. In particular we find a correlation between initial data and both the shock speeds and particle oscillation spectra that match observations in the corresponding regions. When using fourth-order WENO interpolants, we find that while the individual shock profiles at any given time appear non-oscillatory, spurious oscillations appear in the fields after long time integrations. The issue of initialization in hydrostatic equilibrium raises difficult issues. Careful treatment of the gravitational source term can reduce violations of hydrostatic equilibrium, but difficulties remain, primarily due to discontinuities in the piecewise-polynomial reconstructions. In the case of the Euler equations in gravity, the use of high-order methods reduces the violation of hydrostatic equilibrium to a sufficiently low level for the above described results to be obtained. Including various energy flux terms in the equations, however, leads to severe instability when hydrostatic balance is violated. We discuss various strategies to address this problem, including adaptive grid methods.

Bryson, S.↗

NASA NTRS1986

Distribution of solar wind implanted noble gases in lunar samples

The distribution of solar wind implanted noble gases in lunar samples depends on implantation energy, fluence, diffusion, radiation damage and erosion. It is known that at least the lighter rare gases are fractionated after implantation, but the redistribution processes, which mainly drive the losses, are not well understood. Some information about this one can get by looking at the concentration profiles of solar wind implanted He-4 measured by the Gas Ion Probe in single lunar grains. The observed profiles were divided in three groups. These groups are illustrated and briefly discussed.

Kiko, J.↗

NASA NTRS1988

Threshold pump power of a solar-pumped dye laser

Threshold solar power for dye laser pumping has been determined by measuring the gain of a rhodamine 6G dye laser amplifier at various solar-simulated irradiances on an amplifier cell. The measured threshold was 20,000 solar constants (2.7 kW/sq cm) for the dye volume of 2 x 5 x 40 cu mm and the optimum dye concentration of 0.001 M. The threshold is about one-third of that achievable with a high-intensity solar concentrator.

Lee, Ja H.↗

NASA NTRS2005

The Distribution of Water in a Viscous Protoplanetary Disk

The distribution of water in the solar nebula is important to understand for a number of reasons. Firstly, in the inner regions of the solar nebula, the concentration of water vapor is expected to have played a major role in determining its oxidation state, and therefore would control which minerals would form there. Secondly, in the outer nebula, water would be a major condensable, making up nearly 50% of the mass of the solids and thus possibly playing a role in determining where giant planets formed. Lastly, liquid water is important for forming and sustaining life, and therefore understanding where and how water was transported to the habitable zone of a a star is critical to understanding how common life may be in the galaxy. Because of its importance, the distribution of water in the solar nebula has been studied by a number of authors. The main transport mechanisms which would determine the distribution of water would be diffusion and gas drag migration. Water vapor and small solids would diffuse in the nebula, moving away from areas of high concentrations. Larger bodies, while also subject to diffusion, though to a lesser extent, would experience gas drag migration, causing them to move inwards with time. The bodies most affected by this transport mechanism would be on the order of 1 meter in size. As objects continued to grow larger, their inertia would also grow, making them nearly immobile to gas drag. While efforts have been made to understand how water would be distributed in a protoplanetary disk, none of the published models simultaneously consider the effects of nebular evolution, transport of material throughout the nebula, and the existence of solids of various sizes at a given location of the nebula. We are currently developing a model which allows for these effects and is consistent with models for the accretion of bodies in the solar nebula.

Ciesla, F. J.↗

NASA NTRS1999

High Temperature Solar Reflector, Its Preparation and Use

A coating-substrate combination having high specular reflectivity at high temperatures reaching 8000 C in a vacuum is described. The substrate comprises pure nickel metal or a nickel-containing metal alloy such as stainless steel having a highly polished reflective surface. The coating is a layer of silver deposited on the substrate to a thickness of 300 A to 3000 A. A 300 A to 5000 A protective coating of silica, alumina or magnesium fluoride is used to cover the silver and to protect it from oxidation. The combination is useful as a parabolic shaped secondary concentrator for collecting solar radiation for generating power or thermal energy for satellite uses. The reflective layer and protective coating preferably are applied to the reflective surface of the substrate by electron beam evaporation or by ion sputtering.

Jaworske, Donald A.↗

NASA NTRS2001

Sources, Sinks, and the Distribution of OH in the Lower Stratosphere

Extensive measurement campaigns by the NASA ER-2 research aircraft have obtained a nearly pole-to-pole database of the species that control HOx (OH + HO2) chemistry. The wide dynamic range of these in situ measurements provides an opportunity to demonstrate empirically the mechanisms that control the HOx system. Measurements in the lower stratosphere show a remarkably tight correlation of OH concentration with the solar zenith angle (SZA). This correlation is nearly invariant over latitudes ranging from 70 S to 90 N and all seasons. An analysis of the production and loss of HOx in terms of the rate determining steps of reaction sequences developed by Johnston and Podolske and Johnston and Kinnison is used to clarify the behavior of the system and to directly test our understanding of the system with observations. Calculations using in situ measurements show that the production rate of HOx is proportional to O3 and ultraviolet radiation flux. The loss rate is proportional to the concentration and the partitioning of NOy (reactive nitrogen) and the concentration of HO2. In the absence of heterogeneous reactions, the partitioning of NOy is controlled by O3 and NOx and the concentration of HO2 is controlled by NOy and O3, so that the removal rate of OH is buffered against changes in the correlation of O3 and NOy. The heterogeneous conversion of NO2 to HNO3 is not an important net source of HO, because production and removal sequences are nearly balanced. Changes in NOy partitioning resulting from heterogeneous chemistry have a large effect on the loss rates of HOx, but little or no impact on the measured abundance of OH. The enhanced loss rates at high NO2/HNO3 are offset in the data set examined here by enhanced production rates resulting from increased photolysis rates resulting from the decreased O3 column above the ER-2.

Hanisco, T. F.↗