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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 1,189 records · Page 66
All sourcesNASA NTRSDOE OSTI
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 NTRS1980

A base-metal conductor system for silicon solar cells

Solder, copper, and silver are evaluated as conductor layer metals for silicon solar cell metallization on the basis of metal price stability and reliability under operating conditions. Due to its properties and cost, copper becomes an attractive candidate for the conductor layer. It is shown that nickel operates as an excellent diffusion barrier between copper and silicon while simultaneously serving as an electrical contact and mechanical contact to silicon. The nickel-copper system may be applied to the silicon by plating techniques utilizing a variety of plating bath compositions. Solar cells having excellent current-voltage characteristics are fabricated to demonstrate the nickel-copper metallization system.

Coleman, M. G.↗
NASA NTRS2004

Supergranule Diffusion and Active Region Decay

Models of the Sun's magnetic dynamo include turbulent diffusion to parameterize the effects of convective motions on the evolution of the Sun's magnetic field. Supergranules are known to dominate the evolution of the surface magnetic field structure as evidenced by the structure of both the active and quiet magnetic network. However, estimates for the dif hivity attributed to su perymules differ by an order of magnitude from about 100 km sup2/s to more than 1000 km sup2/s. We examine this question of the e i v i t y using three merent approaches. 1) We study the decay of more than 30,000 active regions by determining the rate of change in the sunspot area of each active region from day-to-day. 2) We study the decay of a single isolated active region near the time of solar minimum by examining the magnetic field evolution over five solar rotations fiom SOHOMDI magnetograms obtained at 96-minute intervals. 3) We study the characteristics of supergranules that influence the estimates of their diffusive properties - flow speeds and lifetimes as functions of size - fiom SOHO/MDI Dopplergrams.

Hathaway, David H.↗
NASA NTRS2004

On Orbit Daytime Solar Heating Effects: A Comparison of Ground Chamber Arcing Results

The purpose of the current experiment is to make direct comparisons between the arcing results obtained from the diffusion pumped vertical chamber and our newly renovated Teney vacuum chamber which is equipped with a cryogenic pump. Recall that the prior reported results obtained for the Vertical chamber were nominal at best, showing only a slight reduction in the arc rate after 5 heating cycles at the lower bias potentials and virtually no changes at high potential biases. It was concluded that the vertical chamber was unable to remove enough water vapor from the chamber to adequately test the arcing criterion. Because the cryo-pumped Teney chamber has a ten times better pumping speed, (40,000 liters per sec compared to 4,000 liters per sec for the diffusion pumped vertical chamber), a decision was made to retest that experiment in both the Teney and Vertical vacuum chambers. A comparison of the various data is presented with encouraging results.

Galofaro, J.↗
NASA NTRS2004

On-Orbit Daytime Solar Heating Effects: A Comparison of Ground Chamber Arcing Results

The purpose of the current experiment is to make direct comparisons between the arcing results obtained from the diffusion pumped vertical chamber and our newly renovated Teney vacuum chamber which is equipped with a cryogenic pump. Recall that the prior reported results obtained for the Vertical chamber were nominal at best, showing only a slight reduction in the arc rate after five heating cycles at the lower bias potentials and virtually no changes at high potential biases. It was concluded that the vertical chamber was unable to remove enough water vapor from the chamber to adequately test the arcing criterion. Because the cryo-pumped Teney chamber has a ten times better pumping speed, (40,000 liters per sec compared to 4,000 liters per sec for the diffusion pumped vertical chamber), a decision was made to retest that experiment in both the Teney and Vertical vacuum chambers. A comparison of the various data is presented with encouraging results.

Galofaro, J.↗
NASA NTRS1985

Solar activity beyond the disk and variations of the cosmic ray gradient

Part of galactic cosmic rays (CR) observed near the Earth and on the Earth come from beyond-disk regions of circumsolar space. But CR of those energies which undergo substantial modulation cover too large a path across the lines of force of the interplanetary magnetic field (IMF) in order that they could provide an effective transfer of information about beyond-disk solar activity. And if it is still possible, the most probable channel for transferring such information must be a neutral layer of heliomagnetosphere in which the transverse CR transport is facilitated by their drift in an inhomogeneous magnetic field. A simple diffusion model for an expected CR variation in a neutral layer near the Earth is discussed. It is of importance that variations of the CR gradient are not at all always accompanied by considerable variations of IMF and solar wind velocity at the point of observation.

Belov, A. V.↗
NASA NTRS2010

InGaP Heterojunction Barrier Solar Cells

A new solar-cell structure utilizes a single, ultra-wide well of either gallium arsenide (GaAs) or indium-gallium-phosphide (InGaP) in the depletion region of a wide bandgap matrix, instead of the usual multiple quantum well layers. These InGaP barrier layers are effective at reducing diode dark current, and photogenerated carrier escape is maximized by the proper design of the electric field and barrier profile. With the new material, open-circuit voltage enhancements of 40 and 100 mV (versus PIN control systems) are possible without any degradation in short-circuit current. Basic tenets of quantum-well and quantum- dot solar cells are utilized, but instead of using multiple thin layers, a single wide well works better. InGaP is used as a barrier material, which increases open current, while simultaneously lowering dark current, reducing both hole diffusion from the base, and space charge recombination within the depletion region. Both the built-in field and the barrier profile are tailored to enhance thermionic emissions, which maximizes the photocurrent at forward bias, with a demonstrated voltage increase. An InGaP heterojunction barrier solar cell consists of a single, ultra-wide GaAs, aluminum-gallium-arsenide (AlGaAs), or lower-energy-gap InGaP absorber well placed within the depletion region of an otherwise wide bandgap PIN diode. Photogenerated electron collection is unencumbered in this structure. InGaAs wells can be added to the thick GaAs absorber layer to capture lower-energy photons.

Welser, Roger E.↗
NASA NTRS1972

Solar wind rare gas analysis: Trapped solar wind helium and neon in Surveyor 3 material

The He-4 and Ne-20 contents in sections of the Surveyor 3 support strut samples were determined by optical and scanning electron microscopy and are compared to the results of the Apollo solar wind composition (SWC) experiments. The He-4/Ne-20 ratio in the samples from the sunlit side of the strut was approximately 300; the ratios determined in Apollo 12 lunar fines and SWC foil were below 100. The He-4/He-3 ratios were also determined, and the ratio obtained from Surveyor 3 material is higher than those found with Apollo 11 and 12 SWC experiments. The effects of spallation by cosmic rays or solar protons, stripping by cosmic ray or energetic solar alpha particles, recycling of solar wind He and radiogenic Ne, He from terrestrial atmosphere, mass discrimination near the moon, mass dependence of trapping probability, diffusion, and contamination by lunar dust are considered.

Buehler, F.↗
NASA NTRS1972

Large scale photospheric magnetic field: The diffusion of active region fields

The large-scale phototospheric magnetic field was computed by allowing observed active region fields to diffuse and to be sheared by differential rotation in accordance with the Leighton (1969) magneto-kinematic model of the solar cycle. The differential rotation of the computed field patterns as determined by autocorrelation curves is similar to that of the observed photospheric field, and poleward of 20 deg. latitude both are significantly different from the differential rotation of the long-lived sunspots (Newton and Nunn, 1951) used as an input into the computations.

Schatten, K. H.↗
NASA NTRS1979

Stochastic acceleration of solar flare protons

The acceleration of solar flare protons by the cyclotron damping of intense Alfven wave turbulence in a magnetic trap is considered. The energy diffusion coefficient is computed for a near-isotropic distribution of super-Alfvenic protons, and a steady-state solution for the particle spectrum is found for both transit-time and diffusive losses out of the ends of the trap. The acceleration time to a characteristic energy of about 20 MeV per nucleon can be as short as 10 sec. On the basis of phenomenological arguments, it is inferred that the Alfven wave spectrum typically has an inverse square frequency dependence and that the correlation time of the turbulence lies in the range between 0.5 and 50 msec.

Barbosa, D. D.↗
NASA NTRS1980

Apparent luminosity of solar power satellites

The objective of this investigation was a quantitative characterization of solar power satellite luminosity as seen from the earth. The reflective characteristics of the reference photovoltaic satellite configurations are defined. Diffuse reflection from a single satellite will, at maximum, fall between magnitudes -4 and -5. A 60-satellite fleet will have a maximum total luminosity equivalent to a single object of magnitude -9. Specular reflections from the array and antenna will be of magnitude -12 to -15, but visible only occasionally for about 2 minutes at a given location. Methods of preventing specular reflections from striking the earth are presented. Thermal cycle power conversion systems are discussed qualitatively as a means of reducing diffuse luminosity.

Livingston, L. E.↗
NASA NTRS1982

Membrane separation technology in the 1980s

The current status of membrane technology is assessed and industrial processes in which membrane technology could effect energy savings or other advantages are identified. The extension of current trends is recommended; i.e., the development of ultrathin and highly permselective membranes, the use of specific carriers to enhance permselectivity and permit 'uphill' diffusion, and the improvement of separation efficiency. Membranes are predicted to be important in biotechnology and in the production of solar energy. Guidelines indicating where and how to look for opportunities where evolving membrane technology might fit are provided.

Lonsdale, H. K.↗
NASA NTRS1982

Propagation of energetic particles in the solar wind

A summary is given of recent results from the direct determination of the charge states of He, C, O, and Fe. These results are used in discussing compositional variations during individual solar particle events. It is shown that ratio changes by a factor of approximately 10 during the onset phase of solar particle events can be explained not only by rigidity-dependent interplanetary propagation but also by rigidity-dependent diffusive propagation in the corona. Increasing experimental evidence is seen that other processes, such as compositional variations at the source and discontinuities of the interplanetary magnetic field separating two different particle populations, may be important. No common explanation is seen for all the variations, and it is concluded that each must be investigated on its own.

Klecker, B.↗
NASA NTRS1985

The 1973-1984 Solar Modulation of Cosmic Ray Nuclei

As a continuation of the program of solar modulation studies, new measurements were carried out with the cosmic ray telescope on the Earth satellite IMP-8, of the intensity time variations and the energy spectra of galactic cosmic ray protons, helium, carbon and oxygen from 1980 through 1984 including the recent solar maximum. In order to test the applicability of a steady state model of solar modulation during a period which includes times of rapidly changing modulation, these fluxes were equated with the predictions of a conventional model of solar modulation which assumes equilibrium between modulation mechanisms. It is found that for a reasonable range of variations of the diffusion coefficient the model predictions can be made to agree with the measurements at essentially all times during the studied period. The model can account also for the observed hysteresis effects between cosmic rays of different rigidities.

Garcia-Munoz, M.↗
NASA NTRS1992

High energy gamma ray observations

Since the trajectories of astrophysical charged particles are bent by magnetic fields and normally curl many times before their detection, their origin may not be inferred from their directions as is the case with photons. Fortunately, charged particles reveal their presence through interactions in many instances leading to high-energy gamma rays. Bremsstrahlung, Compton, synchrotron, and curvature radiation all generally have a monotonically decreasing energy spectra reflecting that of the parent particles, whereas nucleon-nucleon radiation has a maximum at about 70 MeV reflecting the nature of the interaction process. Gamma radiation has been seen coming from neutron stars in pulses with the same period as the radio pulsar. Solar gamma rays also have been seen, as have short bursts of gamma rays whose origin remain a mystery. Galactic diffuse gamma radiation reveals the distribution of cosmic rays in our Galaxy. Beyond our Galaxy, active galaxies are seen in gamma rays implying a huge energy in the form of cosmic rays to be present there. The Optically Violent Variable quasar 3C 279 is particularly astounding. During an active state 3C 279 was seen to be emitting approximately 10 exp 48 erg/s if its radiation is isotropic.

Fichtel, Carl E.↗
NASA NTRS2009

BRDF Calibration of Sintered PTFE in the SWIR

Satellite instruments operating in the reflective solar wavelength region often require accurate and precise determination of the Bidirectional Reflectance Distribution Function (BRDF) of laboratory-based diffusers used in their pre-flight calibrations and ground-based support of on-orbit remote sensing instruments. The Diffuser Calibration Facility at NASA's Goddard Space Flight Center is a secondary diffuser calibration standard after NEST for over two decades, providing numerous NASA projects with BRDF data in the UV, Visible and the NIR spectral regions. Currently the Diffuser Calibration Facility extended the covered spectral range from 900 nm up to 1.7 microns. The measurements were made using the existing scatterometer by replacing the Si photodiode based receiver with an InGaAs-based one. The BRDF data was recorded at normal incidence and scatter zenith angles from 10 to 60 deg. Tunable coherent light source was setup. Broadband light source application is under development. Gray-scale sintered PTFE samples were used at these first trials, illuminated with P and S polarized incident light. The results are discussed and compared to empirically generated BRDF data from simple model based on 8 deg directional/hemispherical measurements.

Georgiev, Georgi T.↗
NASA NTRS2023

New Mie Scattering Diffuse Targets Development and Characterization

Earth science remote sensing observations require the detection and measurement of light originating from bright targets, such as clouds, and darker targets, such as an open ocean. This requirement drives the need to design, develop, and characterize improved calibration targets in support of current and future NASA instruments. New diffuse targets to be used as spectral albedo calibration standards were developed and characterized. The new targets based on fused silica or/and pressed and sintered Polytetrafluoroethylene (PTFE) were developed to be Earth scene specific. The various reflectance levels are achieved by modifying the material parameters, thickness, and surface finish. The new targets were characterized in laboratory and simulated space environments. We acquired high accuracy reflectance and transmittance data using a precision optical scatterometer and spectrophotometer located in the NASA Goddard Space Flight Center (GSFC) Diffuser Calibration Lab. The Total hemispherical reflectance (THR) and Bidirectional Reflectance Distribution Function (BRDF) were measured over the range of solar incident and scattered elevation and azimuthal angles typically realized on orbit by remote sensing instruments. We intend to space certify the new calibration targets after concluding on-orbit testing on the International Space Stations (ISS) scheduled for the second half of 2023.

Georgi Georgiev↗