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NASA NTRS1977

Advanced high efficiency wraparound contact solar cell

A significant advancement in the development of thin high efficiency wraparound contact silicon solar cells has been made by coupling space and terrestrial processing procedures. Although this new method for fabricating cells has not been completely reduced to practice, some of the initial cells have delivered over 20 mW/sq cm when tested at 25 C under AMO intensity. This approach not only yields high efficiency devices, but shows promise of allowing complete freedom of choice in both the location and size of the wraparound contact pad area.

Scott-Monck, J. A.↗

NASA NTRS1978

Optical, spin-resonance, and magnetoresistance studies of /tetrathiatetracene/2/iodide/3 - The nature of the ground state

A recent investigation in which Isett and Perez-Albuerne (1977) found that (tetrathiatetracene)2(iodine)3 is a stable organic metal down to 3.3 K is of considerable interest. In view of the diversity of suggestions made regarding this compound, measurements, were made of its electrical, magnetic, and optical properties. The results obtained indicate a metallic state at high temperatures, but also support a nonmetallic state at temperatures below 30 K. At 20-30 K, a metal-to-insulator phase transition occurs. This is indicated by the onset of a large and positive magnetoresistance, the leveling off in the temperature dependence of the ESR linewidth, and by recent derivative analysis of the electrical conductivity in this region. The investigated compound represents an interesting one-dimensional electronic system in which it may be possible to study the combined effects of disorder and interchain coupling on charge transport processes.

Somoano, R. B.↗

NASA NTRS1980

Fabry-Perot-interferometer imaging system for thermospheric temperature and wind measurements

Doppler-broadened Fabry-Perot fringes of weak (less than 1-kR) auroral forbidden O I 5577- and 6300-A emissions have been detected in real time (1/60 sec) with the aid of a low-light level image-orthicon TV camera coupled to a two-stage image intensifier. The imaging scheme permits static-mode operation of a Fabry-Perot interferometer. For maximum use of all the information contained in every TV frame, each circular fringe may be sectioned into several annuli, and the corresponding annuli from all rings are summed to yield an intensity value. This procedure for deriving a fringe profile requires a video digitizer coupled to a digital processing system and should provide fast real-time (1/60 sec) measurements of E- and F-region temperatures and winds. With forbidden O I 5577-A intensity of 750 R, visually prominent TV images of the Fabry-Perot fringes were recorded in 0.5 sec, and the temperature of the emitting region was determined from two percent of the total information in the TV image.

Sivjee, G. G.↗

NASA NTRS1980

The JPL parabolic dish project

The parabolic dish solar collector is a highly versatile concentrating collector system that can produce heat for many thermal processes and electricity by coupling the collector to a suitable heat engine. This paper discusses a project for the development of these collector systems and summarizes contracts with industry for developing the dish subsystems which include concentrator, receiver, and heat engine. An early market for dishes is the dispersed small community market which depends heavily on oil to operate diesel or steam turbine plants in order to generate electricity. The present contracts with industry for conducting engineering experiments using the developed dish hardware to demonstrate the technology in these early opportunity markets is also discussed.

Truscello, V. C.↗

NASA NTRS1980

Computation of the shock-wave boundary layer interaction with flow separation

The boundary layer concept is used to describe the flow near the wall. The external flow is approximated by a pressure displacement relationship (tangent wedge in linearized supersonic flow). The boundary layer equations are solved in finite difference form and the question of the presence and unicity of the solution is considered for the direct problem (assumed pressure) or converse problem (assumed displacement thickness, friction ratio). The coupling algorithm presented implicitly processes the downstream boundary condition necessary to correctly define the interacting boundary layer problem. The algorithm uses a Newton linearization technique to provide a fast convergence.

Ardonceau, P.↗

NASA NTRS1980

Excitation of the b 3 Sigma u + state of H2 by electron impact - Semiclassical exchange potentials at intermediate energies

Integrated and differential cross sections for the excitation of the b 3 Sigma u + state of H2, from the ground state, by electron impact, are presented. The energy range of interest is 10.5 to 40.0 eV. The close-coupling equations for this process are solved in five different exchange approximations: exact two-electron exchange terms, no orthogonality; exact two-electron exchange terms, orthogonality; semiclassical exchange terms, no orthogonality, with barrier term; semiclassical exchange terms, no orthogonality, no barrier term; and semiclassical exchange terms, orthogonality, with barrier term. The purpose is to judge the reliability of the semiclassical exchange approximation for electronic excitation of molecules by electron impact at intermediate energies. The results are compared with recent theoretical estimates for the same process.

Weatherford, C. A.↗

NASA NTRS1981

Electrical behavior of a Shuttle Electrodynamic Tether System /SETS/

Many novel electrodynamic and space plasma physics experiments can be done from the space shuttle using a gravity gradient stabilized subsatellite tethered 10-30 km above the Orbiter via a long, conducting wire which is insulated from the ionospheric plasma. This system, called the Shuttle Electrodynamic Tether System (SETS), is described in the present paper with emphasis upon the various electrical processes which determine its coupling to the ambient plasma. The three most important physical effects include sheath formation and electron collection by the subsatellite, the generation of a large emf through the orbital motion of the tether across geomagnetic field lines, and the active ejection of electrons from the Orbiter into the surrounding ionosphere. An electrical circuit analogy is presented for SETS together with a brief outline of possible areas related to the artificial generation of magnetohydrodynamic waves.

Banks, P. M.↗

NASA NTRS1982

Application of a transonic potential flow code to the static aeroelastic analysis of three-dimensional wings

Since the aerodynamic theory is nonlinear, the method requires the coupling of two iterative processes - an aerodynamic analysis and a structural analysis. A full potential analysis code, FLO22, is combined with a linear structural analysis to yield aerodynamic load distributions on and deflections of elastic wings. This method was used to analyze an aeroelastically-scaled wind tunnel model of a proposed executive-jet transport wing and an aeroelastic research wing. The results are compared with the corresponding rigid-wing analyses, and some effects of elasticity on the aerodynamic loading are noted.

Whitlow, W., Jr.↗

NASA NTRS1982

Application of a transonic potential flow code to the static aeroelastic analysis of three-dimensional wings

A method for including elastic effects in steady, transonic wing analysis is presented. Since the aerodynamic theory is nonlinear, the method requires the coupling of two iterative processes - an aerodynamic analysis and a structural analysis. A full potential analysis code, FL022, is combined with a linear structural analysis to yield aerodynamic load distributions on and deflections of elastic wings. This method was used to analyze an aeroelastically-scaled wind tunnel model of a proposed executive-jet transport wing and an aeroelastic research wing. The results are compared with the corresponding rigid-wing analyses, and some effects of elasticity on the aerodynamic loading are noted.

Whitlow, W., Jr.↗

NASA NTRS1985

Cyanobacterial mats: Microanalysis of community metabolism

The microbial communities in two sites were studied using several approaches: (1) light microscopy; (2) the measurement of microprofiles of oxygen and sulfide at the surface of the microbial mat; (3) the study of diurnal variation of oxygen and sulfides; (4) in situ measurement of photosynthesis and sulfate reduction and study of the coupling of these two processes; (5) measurement of glutathione in the upper layers of the microbial mat as a possible oxygen quencher; (6) measurement of reduced iron as a possible intermediate electron donor along the established redoxcline in the mats; (7) measurement of dissolved phosphate as an indicator of processes of break down of organic matter in these systems; and (8) measurement of carbon dioxide in the interstitial water and its delta C-13 in an attempt to understand the flow of CO2 through the systems. Microbial processes of primary production and initial degradation at the most active zone of the microbial mat were analyzed.

Cohen, Y.↗

NASA NTRS1984

MOSAIC

The Mosaicked Optical Self-scanned Array Imaging Camera (MOSAIC), is a 50 sq cm active area detector system encompassing 5.76 million picture elements. This camera is being developed for use in astronomical instrumentation requiring the use of large area imaging detectors with high resolution photon counting capability in the space ultraviolet. This paper gives a descriptive outline of the MOSAIC camera system including: the 100 mm diameter microchannel plate intensifier, the 3 x 3 array of 800 x 800 pixel charge coupled devices, the signal processing and buffer storage subsystem, the electronic support and control subsystem, and the data processing subsystem. Performance characteristics of the camera and its subsystems are presented, based on system analysis.

Williams, J. T.↗

NASA NTRS1986

Sliding Seal Materials for Adiabatic Engines, Phase 2

An essential task in the development of the heavy-duty adiabatic diesel engine is identification and improvements of reliable, low-friction piston seal materials. In the present study, the sliding friction coefficients and wear rates of promising carbide, oxide, and nitride materials were measured under temperature, environmental, velocity, and loading conditions that are representative of the adiabatic engine environment. In addition, silicon nitride and partially stabilized zirconia disks were ion implanted with TiNi, Ni, Co, and Cr, and subsequently run against carbide pins, with the objective of producing reduced friction via solid lubrication at elevated temperature. In order to provide guidance needed to improve materials for this application, the program stressed fundamental understanding of the mechanisms involved in friction and wear. Electron microscopy was used to elucidate the micromechanisms of wear following wear testing, and Auger electron spectroscopy was used to evaluate interface/environment interactions which seemed to be important in the friction and wear process. Unmodified ceramic sliding couples were characterized at all temperatures by friction coefficients of 0.24 and above. The coefficient at 800 C in an oxidizing environment was reduced to below 0.1, for certain material combinations, by the ion implanation of TiNi or Co. This beneficial effect was found to derive from lubricious Ti, Ni, and Co oxides.

Lankford, J.↗

NASA NTRS1987

Recent research in snow hydrology

Recent work on snow-pack energy exchange has involved detailed investigations on snow albedo and attempts to integrate energy-balance calculations over drainage basins. Along with a better understanding of the EM properties of snow, research in remote sensing has become more focused toward estimation of snow-pack properties. In snow metamorphism, analyses of the physical processes must now be coupled to better descriptions of the geometry of the snow microstructure. The dilution method now appears to be the best direct technique for measuring the liquid water content of snow; work on EM methods continues. Increasing attention to the chemistry of the snow pack has come with the general focus on acid precipitation in hydrology.

Dozier, Jeff↗

NASA NTRS1988

Auroral zone ion composition

The paper discusses the auroral zone and its role as the region of exchange of warm and hot plasmas between the magetosphere and ionosphere. Consideration is then given to the ion mass, energy, and angle distributions observed on a typical midaltitude auroral zone crossing and the central role of oxygen ions as a tracer of the processes involved in the coupling of ionospheric and magnetospheric plasmas. The successful operation of the Swedish Viking satellite in 1986 is noted.

Peterson, W. K.↗

NASA NTRS1990

The composite load spectra project

Probabilistic methods and generic load models capable of simulating the load spectra that are induced in space propulsion system components are being developed. Four engine component types (the transfer ducts, the turbine blades, the liquid oxygen posts and the turbopump oxidizer discharge duct) were selected as representative hardware examples. The composite load spectra that simulate the probabilistic loads for these components are typically used as the input loads for a probabilistic structural analysis. The knowledge-based system approach used for the composite load spectra project provides an ideal environment for incremental development. The intelligent database paradigm employed in developing the expert system provides a smooth coupling between the numerical processing and the symbolic (information) processing. Large volumes of engine load information and engineering data are stored in database format and managed by a database management system. Numerical procedures for probabilistic load simulation and database management functions are controlled by rule modules. Rules were hard-wired as decision trees into rule modules to perform process control tasks. There are modules to retrieve load information and models. There are modules to select loads and models to carry out quick load calculations or make an input file for full duty-cycle time dependent load simulation. The composite load spectra load expert system implemented today is capable of performing intelligent rocket engine load spectra simulation. Further development of the expert system will provide tutorial capability for users to learn from it.

Newell, J. F.↗

NASA NTRS1990

Magnetic pulsations at the quasi-parallel shock

The plasma and field properties of large-amplitude magnetic field pulsatins upstream from the quasi-parallel region of the earth's bow shock are examined in high time resolution using data from ISEE 1 and 2. The relative timing of the magnetic field profiles observed at the two spacecraft shows that some of the pulsations are convecting antisunward across the spacecraft while others are brief out/in motions of bow shock across the spacecraft. Pulsations with both timing signatures are the site of slowing and heating of the solar wind plasma. The ions tend to be only weakly heated in the convecting pulsations, while within the out/in pulsations the ion heating can be quite substantial but variable. This variation occurs not only from pulsation to pulsation but also from point to point within a given pulsation. In general, the hottest distributions within the out/in pulsations tend to occur in regions of lower density and field strength. Magnetic pulsations bear a number of similarities to previously identified hot diamagnetic cavity events as well as to more durable crossings of the quasi-parallel shock itself. These various phenomena may be different manifestations of the same basic physical processes, in particular the coupling of coherently reflected ions to the solar wind beam.

Thomsen, M. F.↗

NASA NTRS1991

Aircraft laser derived chlorophyll distribution across the Iceland-Faeroe front

The ocean surface color (water-leaving radiances) and thermal structure across the Iceland-Faeroe Front under both clear and cloudy conditions were measured from a NASA research aircraft on 25 May 1989. The measurements were made along four north-south lines that were 125 km in length and spaced 35 km apart. The color measurements were made with a 14 channel, non-polarized Multispectral Airborne Radiometer System (MARS) while the thermal data were collected by a thermal radiometer and aircraft bathythermographs. The satellite imagery (NOAA AVHRR) sequence show the development of meanders through the frontal region. These aircraft ocean color and thermal data characterize the biological distribution and are closely coupled to the physical processes occurring in the frontal systems. The ratio of several channels of the ocean color data are used to determine the surface chlorophyll. The retrieved data correlate well with laser-induced chlorophyll fluorescence obtained at the same time and historical chlorophyll data. The observed chlorophyll patchiness appearing across the Iceland-Faeroe Front is believed to be directly and indirectly related to primary and secondary circulation processes in ocean frontal systems. High chlorophyll concentrations were observed on the north side of the front and are inferred to be the result from the advection of Icelandic Coastal Water into the region. The sharp chlorophyll decline at and south of the thermal frontal boundary is clearly related to the subsurface thermal structure.

Arnone, Robert A.↗

NASA NTRS1991

Numerical study of high-area-ratio H2/O2 rocket nozzles

Calculations were made for high-area-ratio H2/O2 rocket nozzles by using the RPLUS code which employs an implicit finite volume, lower-upper symmetric successive over-relaxation scheme to solve the Navier-Stokes equations and the species equations in a coupled manner. The combustion processes of hydrogen and oxygen are modeled by an 8-species and 18-step reaction mechanism, and the turbulence is simulated by the Baldwin-Lomax turbulence model with a pressure gradient correction on the van Driest's damping constant in the inner-layer model. The calculated results for two different rocket nozzles are presented as contours, profiles, and performance values. The predicted specific impulse and thrust agree well with the experimental data and those from the industry standard code. It is demonstrated that the RPLUS code can be used for analysis of rocket nozzles.

Kim, S. C.↗