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  • 1
    Publication Date: 2019-06-28
    Description: Wind tunnel tests have been conducted on an NACA 2412 airfoil section at Reynolds number of 2.2 x 10(exp 6) and Mach number of 0.13. Detailed measurements of flow fields associated with turbulent boundary layers have been obtained at angles of attack of 12.4 degrees, 14.4 degrees, and 16.4 degrees. Pre- and post-separated velocity and pressure survey results over the airfoil and in the associated wake are presented. Extensive force, pressure, tuft survey, hot-film survey, local skin friction, and boundary layer data are also included. Pressure distributions and separation point locations show good agreement with theory for the two layer angles of attack. Boundary layer displacement thickness, momentum thickness, and shape factor agree well with theory up to the point of separation. There is considerable disparity between extent of flow reversal in the wake as measured by pressure and hot-film probes. The difference is attributed to the intermittent nature of the flow reversal.
    Keywords: AERODYNAMICS
    Type: NASA-CR-197497 , NAS 1.26:197497 , AR77-3
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  • 2
    Publication Date: 2019-07-13
    Description: The implementation of a two-equation k-omega turbulence model into the NPARC flow solver is described. Motivation for the selection of this model is given, major code modifications are outlined, new imputs to the code are described, and results are presented for several validation cases: an incompressible flow over a smooth flat plate, a subsonic diffuser flow, and a shock-induced separated flow. Comparison of results with the k-epsilon model indicate that the k-omega model predicts simple flows equally well whereas, for adverse pressure gradient flows, the k-omega model outperforms the other turbulence models in NPARC.
    Keywords: AERODYNAMICS
    Type: NASA-TM-107080 , NAS 1.15:107080 , E-9955 , AIAA PAPER 96-0383 , NIPS-96-08118 , Aerospace Sciences Meeting and Exhibit; Jan 15, 1996 - Jan 18, 1996; Reno, NV; United States
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  • 3
    Publication Date: 2019-07-13
    Description: An approach for solving the compressible Euler and Navier-Stokes equations upon meshes composed of nearly arbitrary polyhedra is described. Each polyhedron is constructed from an arbitrary number of triangular and quadrilateral face elements, allowing the unified treatment of tetrahedral, prismatic, pyramidal, and hexahedral cells, as well the general cut cells produced by Cartesian mesh approaches. The basics behind the numerical approach and the resulting data structures are described. The accuracy of the mixed volume grid approach is assessed by performing a grid refinement study upon a series of hexahedral, tetrahedral, prismatic, and Cartesian meshes for an analytic inviscid problem. A series of laminar validation cases are made, comparing the results upon differing grid topologies to each other, to theory, and experimental data. A computation upon a prismatic/tetrahedral mesh is made simulating the laminar flow over a wall/cylinder combination.
    Keywords: AERODYNAMICS
    Type: NASA-TM-107135 , NAS 1.15:107135 , AIAA PAPER 96-0762 , E-10065 , NIPS-96-07909 , Aerospace Sciences Meeting and Exhibit; Jan 15, 1996 - Jan 18, 1996; Reno, NV; United States
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  • 4
    Publication Date: 2011-08-24
    Description: Measurements of wing buffeting, using root strain gages, were made in the NASA Langley 0.3 m cryogenic wind tunnel to refine techniques which will be used in larger cryogenic facilities such as the United States National Transonic Facility (NTF) and the European Transonic Wind Tunnel (ETW). The questions addressed included the relative importance variations in frequency parameter and Reynolds number, the choice of model material (considering both stiffness and damping) and the effects of static aeroelastic distortion. The main series of tests was made on three half models of slender 65 deg delta wings with a sharp leading edge. The three delta wings had the same planform but widely differing bending stiffnesses and frequencies (obtained by varying both the material and the thickness of the wings). It was known that the steady flow on this configuration would be insensitive to variations in Reynolds number. On this wing at vortex breakdown the spectrum of the unsteady excitation is unusual, having a sharp peak at particular frequency parameter. Additional tests were made on one unswept half-wing of aspect ratio 1.5 with an NPL 9510 aerofoil section, known to be sensitive to variations in Reynolds number at transonic speeds. The test Mach numbers were M = 0.21 and 0.35 for the delta wings and to M = 0.30 for the unswept wing. On this wing the unsteady excitation spectrum is fairly flat (as on most wings). Hence correct representation of the frequency parameter is not particularly important.
    Keywords: AERODYNAMICS
    Type: Aeronautical Journal (ISSN 0001-9240); 99; 981; p. 1-14
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  • 5
    Publication Date: 2011-08-24
    Description: Low temperature Zn diffusion in GaSb, where the minimum temperature was 450 C, was studied. The pseudo-closed box (PCB) method was used for Zn diffusion into GaAs, AlGaAs, InP, InGaAs and InGaAsP. The PCB method avoids the inconvenience of sealed ampoules and proved to be simple and reproducible. The special design of the boat for Zn diffusion ensured the uniformality of Zn vapor pressure across the wafer surface, and thus the uniformity of the p-GaSb layer depth. The p-GaSb layers were studied using Raman scattering spectroscopy and the x-ray rocking curve method. As for the postdiffusion processing, an anodic oxidation was used for a precise thinning of the diffused GaSb layers. The results show the applicability of the PCB method for the large-scale production of the GaSb structures for solar cells.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: ESA, Proceedings of 4th European Space Power Conference (ESPC). Volume 2: Photovoltaic Generators, Energy Storage; p 641-644
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  • 6
    Publication Date: 2011-08-24
    Description: Indium phosphide is considered to be a strong contender for many photovoltaic space applications because of its radiation resistance and its potential for high efficiency. An overview of recent progress is presented, and possible future research directions for indium phosphide space solar cells are discussed. The topics considered include radiation damage studies and space flight experiments.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: ESA, Proceedings of 4th European Space Power Conference (ESPC). Volume 2: Photovoltaic Generators, Energy Storage; p 469-470
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  • 7
    Publication Date: 2011-08-24
    Description: Understanding solar cell response to pulsed laser outputs is important for the evaluation of power beaming applications. The time response of high efficiency GaAs and silicon solar cells to a 25 nS monochromatic pulse input is described. The PC-1D computer code is used to analyze the cell current during and after the pulse for various conditions.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: ESA, Proceedings of 4th European Space Power Conference (ESPC). Volume 2: Photovoltaic Generators, Energy Storage; p 483-485
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  • 8
    Publication Date: 2011-08-24
    Description: Four-terminal mechanically stacked solar cells were developed for advanced space arrays with line-focus reflective concentrators. The top cells are based on AlGaAs/GaAs multilayer heterostructures prepared by low temperature liquid phase epitaxy. The bottom cells are based on heteroepitaxial InP/InGaAs liquid phase epitaxy or on homo-junction GaSb, Zn-diffused structures. The sum of the highest reached efficiencies of the top and bottom cells is 29.4 percent. The best four-terminal tandems have an efficiency of 27 to 28 percent. Solar cells were irradiated with 1 MeV electrons and their performances were determined as a function of fluence up to 10(exp 16) cm(exp-2). It was shown that the radiation resistance of developed tandem cells is similar to the most radiative stable AlGaAs/GaAs cells with a thin p-GaAs photoactive layer.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: ESA, Proceedings of 4th European Space Power Conference (ESPC). Volume 2: Photovoltaic Generators, Energy Storage; p 363-366
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  • 9
    Publication Date: 2011-08-24
    Description: An investigation of solar cells based on AlGaAs/GaAs heterostructures with an internal Bragg reflector as the back-surface reflector is presented. The Bragg reflector is grown by low pressure metalorganic chemical vapor deposition on n-GaAs substrates in a horizontal resistively heated reactor. The Bragg reflector with its maximum reflectance centered at a wavelength of 860 nm consists of 12 pairs of AlAs/GaAs layers. The resulting Bragg reflector has a thickness of 0.072 micrometers for AlAs and 0.059 micrometers for GaAs. The multi-layered quasi-dielectric stack selectively reflects weakly absorbed photons with energies near to the GaAs band gap for a second pass through the photoactive region, thus increasing the photocurrent. The use of the Bragg reflector allows the external quantum efficiency to be increased in the long wavelength of the spectrum. The use of the Bragg reflector and an antireflective coating and prismatic cover allowed an efficiency of 23.4 percent to be obtained.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: ESA, Proceedings of 4th European Space Power Conference (ESPC). Volume 2: Photovoltaic Generators, Energy Storage; p 367-370
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  • 10
    Publication Date: 2011-08-24
    Description: The high efficiency solar cells based on multilayer AlGaAs/GaAs heterostructures, prepared by low temperature liquid phase epitaxy (LPE), were developed and tested. An investigation of the low temperature LPE process for the crystallization of AlGaAs heterostructures of as high as 24.0 to 24.7 percent under AMO conditions at concentration ratios of 20 to 100x, were reached. Developed solar cells show substantial radiation resistance to the damage induced by 3.75 MeV electrons.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: ESA, Proceedings of 4th European Space Power Conference (ESPC). Volume 2: Photovoltaic Generators, Energy Storage; p 359-362
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  • 11
    Publication Date: 2013-08-31
    Description: The Thermal Energy Storage-1 (TES-1) is a flight experiment that flew on the Space Shuttle Columbia (STS-62), in March 1994, as part of the OAST-2 mission. TES-1 is the first experiment in a four experiment suite designed to provide data for understanding the long duration microgravity behavior of thermal energy storage fluoride salts that undergo repeated melting and freezing. Such data have never been obtained before and have direct application for the development of space-based solar dynamic (SD) power systems. These power systems will store solar energy in a thermal energy salt such as lithium fluoride or calcium fluoride. The stored energy is extracted during the shade portion of the orbit. This enables the solar dynamic power system to provide constant electrical power over the entire orbit. Analytical computer codes have been developed for predicting performance of a spaced-based solar dynamic power system. Experimental verification of the analytical predictions is needed prior to using the analytical results for future space power design applications. The four TES flight experiments will be used to obtain the needed experimental data. This paper will focus on the flight results from the first experiment, TES-1, in comparison to the predicted results from the Thermal Energy Storage Simulation (TESSIM) analytical computer code. The TES-1 conceptual development, hardware design, final development, and system verification testing were accomplished at the NASA lewis Research Center (LeRC). TES-1 was developed under the In-Space Technology Experiment Program (IN-STEP), which sponsors NASA, industry, and university flight experiments designed to enable and enhance space flight technology. The IN-STEP Program is sponsored by the Office of Space Access and Technology (OSAT).
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Goddard Space Flight Center, The 1995 Shuttle Small Payloads Symposium; p 31-38
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  • 12
    Publication Date: 2013-08-31
    Description: Analytical investigation of dynamic stall on HAWT (horizontal-axis wind turbines) rotor loads was conducted. Dynamic stall was modeled using the Gormont approach on the MOD-2 rotor, treating the blade as a rigid body teetering about a fixed axis. Blade flapwise bending moments at station 370 were determined with and without dynamic stall for spatial variations in local wind speed due to wind shear and yaw. The predicted mean flapwise bending moments were found to be in good agreement with test results. Results obtained with and without dynamic stall showed no significant difference for the mean flapwise bending moment. The cyclic bending moments calculated with and without dynamic stall effects were substantially the same. None of the calculated cyclic loads reached the level of the cyclic loads measured on the MOD-2 using the Boeing five-minute-average technique.
    Keywords: AERODYNAMICS
    Type: DASCON Engineering, Collected Papers on Wind Turbine Technology; p 41-46
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  • 13
    Publication Date: 2013-08-31
    Description: This paper describes the engineering thought process behind the failure analysis, redesign, and rework of the flight hardware for the Brilliant Eyes Thermal Storage Unit (BETSU) experiment. This experiment was designed to study the zero-g performance of 2-methylpentane as a suitable phase change material. This hydrocarbon served as the cryogenic storage medium for the BETSU experiment which was flown 04 Mar 94 on board Shuttle STS-62. Ground testing had indicated satisfactory performance of the BETSU at the 120 Kelvin design temperature. However, questions remained as to the micro-gravity performance of this unit; potential deviations in ground (1 g) versus space flight (0 g) performance, and how the unit would operate in a realistic space environment undergoing cyclical operation. The preparations and rework performed on the BETSU unit, which failed initial flight qualification, give insight and lessons learned to successfully develop and qualify a space flight experiment.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Goddard Space Flight Center, The 1995 Shuttle Small Payloads Symposium; p 295-302
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  • 14
    Publication Date: 2013-08-31
    Description: The Solar Array Module Plasma Interactions Experiment (SAMPIE) is a flight experiment that flew on the Space Shuttle Columbia (STS-62) in March 1994, as part of the OAST-2 mission. The overall objective of SAMPIE was to determine the adverse environmental interactions within the space plasma of low earth orbit (LEO) on modern solar cells and space power system materials which are artificially biased to high positive and negative direct current (DC) voltages. The two environmental interactions of interest included high voltage arcing from the samples to the space plasma and parasitic current losses. High voltage arcing can cause physical damage to power system materials and shorten expected hardware life. parasitic current losses can reduce power system efficiency because electric currents generated in a power system drain into the surrounding plasma via parasitic resistance. The flight electronics included two programmable high voltage DC power supplies to bias the experiment samples, instruments to measure the surrounding plasma environment in the STS cargo bay, and the on-board data acquisition system (DAS). The DAS provided in-flight experiment control, data storage, and communications through the Goddard Space Flight Center (GSFC) Hitchhiker flight avionics to the GSFC Payload Operations Control Center (POCC). The DAS and the SAMPIE POCC computer systems were designed for telescience operations; this paper will focus on the experiences of the SAMPIE team regarding telescience development and operations from the GSFC POCC during STS-62. The SAMPIE conceptual development, hardware design, and system verification testing were accomplished at the NASA Lewis Research Center (LeRC). SAMPIE was developed under the In-Space Technology Experiment Program (IN-STEP), which sponsors NASA, industry, and university flight experiments designed to enable and enhance space flight technology. The IN-STEP Program is sponsored by the Office of Space Access and Technology (OSAT).
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Goddard Space Flight Center, The 1995 Shuttle Small Payloads Symposium; p 59-72
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  • 15
    Publication Date: 2013-08-31
    Description: A coordinated effort has been underway over the past four years to elevate unstructured-grid methodology to a mature level. The goal of this endeavor is to provide a validated capability to non-expert users for performing rapid aerodynamic analysis and design of complex configurations. The Euler component of the system is well developed, and is impacting a broad spectrum of engineering needs with capabilities such as rapid grid generation and inviscid flow analysis, inverse design, interactive boundary layers, and propulsion effects. Progress is also being made in the more tenuous Navier-Stokes component of the system. A robust grid generator is under development for constructing quality thin-layer tetrahedral grids, along with a companion Navier-Stokes flow solver. This paper presents an overview of this effort, along with a perspective on the present and future status of the methodology.
    Keywords: AERODYNAMICS
    Type: NASA. Lewis Research Center, Surface Modeling, Grid Generation, and Related Issues in Computational Fluid Dynamic (CFD) Solutions; p 289-308
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  • 16
    Publication Date: 2013-08-29
    Description: AstroPower is developing InGaAsSb thermophotovoltaic (TPV) devices. This photovoltaic cell is a two-layer epitaxial InGaAsSb structure formed by liquid-phase epitaxy on a GaSb substrate. The (direct) bandgap of the In(1 - x)Ga(x)As(1 -y)Sb(y) alloy is 0.50 to 0.55 eV, depending on its exact alloy composition (x, y); and is closely lattice-matched to the GaSb substrate The use of the quaternary alloy, as opposed to a ternary alloy - such as, for example, InGaAs/InP - permits low bandgap devices optimized for 1000 to 1500 C thermal sources with, with at the time, near-exact lattice matching to the GaSb substrate. Lattice-matching is important since even a small degree of lattice mismatch degrades device performance and reliability and increases processing complexity. For bandgaps of 0.52 eV,Fo internal quantum efficiencies as high as 95% have been measured at a wavelength of 2 microns. At 1 micron wavelengths, internal quantum efficiencies of 55% have been observed. The open-circuit voltage at currents of 0.3 A/sq cm is 0.220 volts and 0.260 V for current densities of 2 A/sq cm. Fill factors of 56% have also been measured. These preliminary results lead to the conclusion that the GaSb-based quaternary compounds provide a viable and high performance energy conversion solution for thermophotovoltaic systems operating with 1000 to 1500 C source temperatures.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Lewis Research Center, Proceedings of the 14th Space Photovoltaic Research and Technology Conference (SPRAT 14); p 31
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  • 17
    Publication Date: 2013-08-29
    Description: InP p(+)nn(+) MOCVD solar cells were irradiated with 0.2 MeV and 10 MeV protons to a fluence of 10(exp 13)/sq cm. The degradation of power output, IV behavior, carrier concentration and defect concentration were observed at intermediate points throughout the irradiations. The 0.2 MeV proton irradiated solar cells suffered much greater and more rapid degradation in power output than those irradiated with 10 meV protons. The efficiency losses were accompanied by larger increases in the recombination currents in the 0.2 MeV proton irradiated solar cells. The low energy proton irradiations also had a larger impact on the series resistance of the solar cells. Despite the radiation induced damage, the carrier concentration in the base of the solar cells showed no reduction after 10 MeV or 0.2 MeV proton irradiations and even increased during irradiation with 0.2 MeV protons. In a DLTS study of the irradiated samples, the minority carrier defects H4 and H5 at E(v) + 0.33 and E(v) + 0.52 eV and the majority carrier defects E7 and E10 at E(c)- 0.39 and E(c)-0.74 eV, were observed. The defect introduction rates for the 0.2 MeV proton irradiations were about 20 times higher than for the 10 MeV proton irradiations. The defect E10, observed here after irradiation, has been shown to act as a donor in irradiated n-type InP and may be responsible for obscuring carrier removal. The results of this study are consistent with the much greater damage produced by low energy protons whose limited range causes them to stop in the active region of the solar cell.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: Proceedings of the 14th Space Photovoltaic Research and Technology Conference (SPRAT 14); p 1
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  • 18
    Publication Date: 2019-01-25
    Description: High voltage power systems in space will interact with the space plasma in a variety of ways. One of these, snapover, is characterized by sudden enlargement of the current collection area across normally insulating surfaces generating enhanced electron current collection. Power drain on solar array power systems results from this enhanced current collection. Optical observations of the snapover phenomena in the laboratory indicates a functional relation between glow area and bia potential as a consequence of the fold/cusp bifurcation in chaos theory. Successful characterizations of snapover as a chaotic phenomena may provide a means of snapover prevention and control through chaotic synchronization.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: Proceedings of the 14th Space Photovoltaic Research and Technology Conference (SPRAT 14); p 4
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  • 19
    Publication Date: 2019-01-25
    Description: The PASP-Plus (Photovoltaic Array Space Power Plus Diagnostics) program is a photovoltaic experiment which is flying on the Air Force satellite APEX (Advanced Photovoltaic and Electronics Experiments). The satellite was launched on August 3, 1994 with a Pegasus low-cost launch vehicle. There are two other small experiments on APEX, however PASP-Plus is the largest, uses the most power, and accounts for the largest portion of the data requirements. The satellite is in an elliptical orbit with an apogee of 2552 km and a perigee of 363 km. The inclination is 70 degrees. The PASP-Plus experiment consists of twelve photovoltaic panels containing a total of sixteen separate cell modules. Two of the modules are concentrator modules, while the rest are planar. There are several different solar cell types flying on PASP-Plus including silicon, GaAs on germanium substrates, InP, amorphous silicon, and three multi-bandgap cells. The purpose of this paper is to present some of the data from the first year of the PASP-Plus flight. Cell performance and module thermal performance will be discussed as well as other relevant data.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: Proceedings of the 14th Space Photovoltaic Research and Technology Conference (SPRAT 14); p 3
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  • 20
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    Publication Date: 2019-01-25
    Description: The Astro Edge solar array is a new and innovative reflective low concentrator power generating system which has been selected for the CTA Incorporate/Lockheed Martin Clark spacecraft under the NASA Small Spacecraft Technology Initiative (SSTI) program. In support of this program, Astro Aerospace Corporation has produced one qualification and two flight solar array wings to support a July 1996 launch. The Astro Edge solar array was selected as a new technology to benefit future NASA, military and commercial missions by providing high specific power, high deployed stiffness, low stowed volume, low risk, and cost reduction features which meet the agency's 'better, faster, cheaper' goals. This novel array accounts for five of the thirty-six advanced technologies which the Clark spacecraft will demonstrate. A brief SSTI Astro Edge solar array program overview is presented. Completed qualification and acceptance testing is discussed. Finally, the major discriminators which make the Astro Edge solar array 'better, faster, cheaper' technology are provided.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Lewis Research Center, Proceedings of the 14th Space Photovoltaic Research and Technology Conference (SPRAT 14); p 35
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  • 21
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    Publication Date: 2019-01-25
    Description: Gallium phosphide (GaP) energy converters may be successfully deployed to provide new mission capabilities for spacecraft. Betavoltaic power supplies based on the conversion of tritium beta decay to electricity using GaP energy converters can supply long term low-level power with high reliability. High temperature solar cells, also based on GaP, can be used in inward-bound missions greatly reducing the need for thermal dissipation. Results are presented for GaP direct conversion devices powered by Ni-63 and compared to the conversion of light emitted by tritiarated phosphors. Leakage currents as low as 1.2 x 10(exp -17) A/sq cm have been measured and the temperature dependence of the reverse saturation current is found to have ideal behavior. Temperature dependent IV, QE, R(sub sh), and V(sub oc) results are also presented. These data are used to predict the high-temperature solar cell and betacell performance of GaP devices and suggest appropriate applications for the deployment of this technology.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Lewis Research Center, Proceedings of the 14th Space Photovoltaic Research and Technology Conference (SPRAT 14); p 33
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  • 22
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    Publication Date: 2019-01-25
    Description: Literature on solar array angle of incidence corrections was found to be sparse and contained no tabular data for support. This lack along with recent data on 27 GaAs/Ge 4 cm by 4 cm cells initiated the analysis presented in this paper. The literature cites seven possible contributors to angle of incidence effects: cosine, optical front surface, edge, shadowing, UV degradation, particulate soiling, and background color. Only the first three are covered in this paper due to lack of sufficient data. The cosine correction is commonly used but is not sufficient when the incident angle is large. Fresnel reflection calculations require knowledge of the index of refraction of the coverglass front surface. The absolute index of refraction for the coverglass front surface was not known nor was it measured due to lack of funds. However, a value for the index of refraction was obtained by examining how the prediction errors varied with different assumed indices and selecting the best fit to the set of measured values. Corrections using front surface Fresnel reflection along with the cosine correction give very good predictive results when compared to measured data, except there is a definite trend away from predicted values at the larger incident angles. This trend could be related to edge effects and is illustrated by a use of a box plot of the errors and by plotting the deviation of the mean against incidence angle. The trend is for larger deviations at larger incidence angles and there may be a fourth order effect involved in the trend. A chi-squared test was used to determine if the measurement errors were normally distributed. At 10 degrees the chi-squared test failed, probably due to the very small numbers involved or a bias from the measurement procedure. All other angles showed a good fit to the normal distribution with increasing goodness-of-fit as the angles increased which reinforces the very small numbers hypothesis. The contributed data only went to 65 degrees from normal which prevented any firm conclusions about extreme angle effects although a trend in the right direction was seen. Measurement errors were estimated and found to be consistent with the conclusions that were drawn. A controlled experiment using coverglasses and cells from the same lots and extending to larger incidence angles would probably lead to further insight into the subject area.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Lewis Research Center, Proceedings of the 14th Space Photovoltaic Research and Technology Conference (SPRAT 14); p 26
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  • 23
    Publication Date: 2019-01-25
    Description: Past NASA missions to Mars, Jupiter, and the outer planets were powered by radioisotope thermal generators (RTG's). Although these devices proved to be reliable, their high cost and highly toxic radioactive heat source has made them far less desirable for future planetary missions. This has resulted in a renewed search for alternate energy sources, some of them being photovoltaic (PV) and thermophotovoltaic (TPV). Both of these alternate energy sources convert light/thermal energy directly into electricity. In order to create a viable PV and TPV data base for planetary mission planners and cell designers, we have compiled low temperature low intensity (LILT) I-V data on single junction and multi-junction high efficiency solar cells. The cells tested here represent the latest photovoltaic technology. Using this LILT data to calculate dI(sub SC)/dT, dV(sub OC)/dT, dFF/dT, and also as a function of intensity, an accurate prediction of cell performance under the AMO spectrum can be determined. When combined with QUantum efficiency at Low Temperature (QULT) data, one can further enhance the data by adding spectral variations to the measurements. This paper presents an overview of LILT measurements and is only intended to be used as a guideline for material selection and performance predictions. As single junction and multi-junction cell technologies emerge, new test data must be collected. Cell materials included are Si, GaAs/Ge, GainP/GaAs/Ge, InP, InGaAs/InP, InP/InGaAs/InP, and GainP. Temperatures range as low as -175 C and intensities range from 1 sun to .02 suns.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: Proceedings of the 14th Space Photovoltaic Research and Technology Conference (SPRAT 14); p 2
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  • 24
    Publication Date: 2019-01-25
    Description: When determining the best solar cell technology for a particular space flight mission, accurate prediction of solar cell performance in a space radiation environment is essential. The current methodology used to make such predictions requires extensive experimental data measured under both electron and proton irradiation. Due to the rising cost of accelerators and irradiation facilities, such extensive data sets are expensive to obtain. Moreover, with the rapid development of novel cell designs, the necessary data are often not available. Therefore, a method for predicting cell degradation based on limited data is needed. Such a method has been developed at the Naval Research Laboratory based on damage correlation using 'displacement damage dose' which is the product of the non-ionizing energy loss (NIEL) and the particle fluence. Displacement damage dose is a direct analog of the ionization dose used to correlate the effects of ionizing radiations. In this method, the performance of a solar cell in a complex radiation environment can be predicted from data on a single proton energy and two electron energies, or one proton energy, one electron energy, and Co(exp 60) gammas. This method has been used to accurately predict the extensive data set measured by Anspaugh on GaAs/Ge solar cells under a wide range of electron and proton energies. In this paper, the method is applied to InP solar cells using data measured under 1 MeV electron and 3 MeV proton irradiations, and the calculations are shown to agree well with the measured data. In addition to providing accurate damage predictions, this method also provides a basis for quantitative comparisons of the performance of different cell technologies. The performance of the present InP cells is compared to that published for GaAs/Ge cells. The results show InP to be inherently more resistant to displacement energy deposition than GaAs/Ge.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Lewis Research Center, Proceedings of the 14th Space Photovoltaic Research and Technology Conference (SPRAT 14); p 14
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  • 25
    Publication Date: 2019-01-25
    Description: Advanced materials play an important role in electrochemical energy devices such as batteries, fuel cells, and electrochemical capacitors. They are being used as both electrodes and electrolytes. Sol-gel processing is a versatile solution technique used in fabrication of ceramic materials with tailored stoichiometry, microstructure, and properties. The application of sol-gel processing in the fabrication of advanced electrochemical energy materials will be presented. The potentials of sol-gel derived materials for electrochemical energy applications will be discussed along with some examples of successful applications. Sol-gel derived metal oxide electrode materials such as V2O5 cathodes have been demonstrated in solid-slate thin film batteries; solid electrolytes materials such as beta-alumina for advanced secondary batteries had been prepared by the sol-gel technique long time ago; and high surface area transition metal compounds for capacitive energy storage applications can also be synthesized with this method.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Lewis Research Center, Space Electrochemical Research and Technology. Abstracts; p 37
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  • 26
    facet.materialart.
    Unknown
    In:  Other Sources
    Publication Date: 2019-01-25
    Description: Grid generation plays an integral part in the solution of computational fluid dynamics problems for aerodynamics applications. A major difficulty with standard structured grid generation, which produces quadrilateral (or hexahedral) elements with implicit connectivity, has been the requirement for a great deal of human intervention in developing grids around complex configurations. This has led to investigations into unstructured grids with explicit connectivities, which are primarily composed of triangular (or tetrahedral) elements, although other subdivisions of convex cells may be used. The existence of large gradients in the solution of aerodynamic problems may be exploited to reduce the computational effort by using high aspect ratio elements in high gradient regions. However, the heuristic approaches currently in use do not adequately address this need for high aspect ratio unstructured grids. High aspect ratio triangulations very often produce the large angles that are to be avoided. Point generation techniques based on contour or front generation are judged to be the most promising in terms of being able to handle complicated multiple body objects, with this technique lending itself well to adaptivity. The eventual goal encompasses several phases: first, a partitioning phase, in which the Voronoi diagram of a set of points and line segments (the input set) will be generated to partition the input domain; second, a contour generation phase in which body-conforming contours are used to subdivide the partition further as well as introduce the foundation for aspect ratio control, and; third, a Steiner triangulation phase in which points are added to the partition to enable triangulation while controlling angle bounds and aspect ratio. This provides a combination of the advancing front/contour techniques and refinement. By using a front, aspect ratio can be better controlled. By using refinement, bounds on angles can be maintained, while attempting to minimize the number of Steiner points.
    Keywords: AERODYNAMICS
    Type: NASA. Lewis Research Center, Surface Modeling, Grid Generation, and Related Issues in Computational Fluid Dynamic (CFD) Solutions; p 88
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  • 27
    Publication Date: 2019-01-25
    Description: The experimental performance of a multijunction monolithic In(0.53)Ga(0. 47)As power converter under blackbody irradiation is reported. Eight InGaAs PN junctions grown epitaxially on a semi-insulating wafer were monolithically integrated in series to boost the approximately 0.4 V photovoltage per typical InGaAs junction to over 3 volts for the 1 sq cm chip. This chip was originally designed and characterized for free-space 1.3 micron laser power beaming. This is the first report of such a multijunction TPV. This is not a traditional tandem cell in which the junctions are stacked vertically. The junctions are each about 1mm long by 1 cm wide and are laterally connected across the 1 sq cm device area. This multijunction design has the potential for lower I(sup 2)R power loss since the smaller PN junction area limits the current to one-eighth that of the equivalent surface area. In essence, the current is traded for voltage to avoid the I(sup 2)R loss, analogous to the way power utilities avoid I(sup 2)P loss in high-tension power lines, by transforming the high current, low voltage generated at a power plant into a high voltage at a low current before transmitting the power over great distances.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Lewis Research Center, Proceedings of the 14th Space Photovoltaic Research and Technology Conference (SPRAT 14); p 32
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  • 28
    Publication Date: 2019-01-25
    Description: Progress is reported with respect to the development of ultra-lightweight, high performance, thin, light trapped GaAs solar cells for advanced space power systems. Conversion efficiencies of over 17.7% have been demonstrated for a 3 micron thick, 1 sq cm silicone bonded solar cell. This results in a specific power of over 1020 W/kg. Device parameters were 1.011 V open circuit voltage, 80% fill factor, and a short-circuit current density of 29.5 mA/sq cm . In addition to silicone bonding, the use of electrostatic bonding to attach the coverglass support to the front surface enables an ultra-thin, all back contact design that survives processing temperatures greater than 750 C. This also results in a 10% reduction of the cell weight for a potential specific power of 1270 W/kg. All back contact, ultra-thin, electrostatically bonded GaAs solar cell prototypes have been completed demonstrating an open circuit voltage of 1 volt for a cell base thickness of 1 micron with a 0.5 micron emitter. This technology will result in a revolutionary improvement in survivability, performance, and manufacturability of lightweight GaAs solar cell products for future Earth-orbiting science and space exploration missions. The thin, electrostatically bonded, all back contact GaAs device technology has multiple uses for specialty high performance solar cells and other optoelectronic devices.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Lewis Research Center, Proceedings of the 14th Space Photovoltaic Research and Technology Conference (SPRAT 14); p 24
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  • 29
    Publication Date: 2019-01-25
    Description: Multi-junction solar cells are attractive for space applications because they can be designed to convert a larger fraction of AMO into electrical power at a lower cost than single-junction cells. The performance of multi-junction cells is much more sensitive to the spectral irradiance of the illuminating source than single-junction cells. The design of high efficiency multi-junction cells for space applications requires matching the optoelectronic properties of the junctions to AMO spectral irradiance. Unlike single-junction cells, it is not possible to carry out quantum efficiency measurements using only a monochromatic probe beam and determining the cell short-circuit current assuming linearity of the quantum efficiency. Additionally, current-voltage characteristics can not be calculated from measurements under non-AMO light sources using spectral-correction methods. There are reports in the literature on characterizing the performance of multi junction cells by measuring and convoluting the quantum efficiency of each junction with the spectral irradiance; the technique is of limited value for the characterization of cell performance under AMO power-generating conditions. We report the results of research to develop instrumentation and techniques for characterizing multi junction solar cells for space . An integrated system is described which consists of a standard lamp, spectral radiometer, dual-source solar simulator, and personal computer based current-voltage and quantum efficiency equipment. The spectral radiometer is calibrated regularly using the tungsten-halogen standard lamp which has a calibration based on NIST scales. The solar simulator produces the light bias beam for current-voltage and cell quantum efficiency measurements. The calibrated spectral radiometer is used to 'fit' the spectral irradiance of the dual-source solar simulator to WRL AMO data. The quantum efficiency apparatus includes a monochromatic probe beam for measuring the absolute cell quantum efficiency at various voltage biases, including the voltage bias corresponding to the maximum-power point under AMO light bias. The details of the procedures to 'fit' the spectral irradiance to AMO will be discussed. An assessment of the role of the accuracy of the 'fit' of the spectral irradiance and probe beam intensity on measured cell characteristics will be presented. quantum efficiencies were measured with both spectral light bias and AMO light bias; the measurements show striking differences. Spectral irradiances were convoluted with cell quantum efficiencies to calculate cell currents as function of voltage. The calculated currents compare with measured currents at the 1% level. Measurements on a variety of multi-junction cells will be presented. The dependence of defects in junctions on cell quantum efficiencies measured under light and voltage bias conditions will be presented. Comments will be made on issues related to standards for calibration, and limitations of the instrumentation and techniques. Expeditious development of multi-junction solar cell technology for space presents challenges for cell characterization in the laboratory.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Lewis Research Center, Proceedings of the 14th Space Photovoltaic Research and Technology Conference (SPRAT 14); p 25
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  • 30
    Publication Date: 2019-01-25
    Description: It is well known that the behavior of III-V compound based solar cells is largely controlled by their surface, since the majority of light generated carriers (63% for GaAs and 79% for InP) are created within 0.2 mu m of the surface of the illuminated cell. Consequently, the always observed high surface recombination velocity (SRV) on these cells is a serious limiting factor for their high efficiency performance, especially for those with p-n junction made by either thermal diffusion or ion implantation. A good surface passivation layer, ideally a grown oxide as opposed to a deposited one, will cause a significant reduction in the SRV without adding interface problems, thus improving the performance of III-V compound based solar cells. Another significant benefit to the overall performance of the solar cells can be achieved by a substantial reduction of their large surface optical reflection by the use of a well designed antireflection (AR) coating. In this paper, we demonstrate the effectiveness of using a chemically grown thermally and chemically stable oxide, not only for surface passivation but also as an integral part of a 3-layer AR coating for thermally diffused p+n InP solar cells. A phosphorus-rich interfacial oxide, In(PO3)3, is grown at the surface of the p+ emitter using an etchant based on HNO3, o-H3PO4 and H2O2. This oxide has the unique properties of passivating the surface as well as serving as an efficient antireflective layer yielding a measured record high AMO open-circuit voltage of 890.3 mV on a thermally diffused InP(Cd,S) solar cell. Unlike conventional single layer AR coatings such as ZnS, Sb2O3, SiO or double layer AR coatings such as ZnS/MgF2 deposited by e-beam or resistive evaporation, this oxide preserves the stoichiometry of the InP surface. We show that it is possible to design a three-layer AR coating for a thermally diffused InP solar cell using the In(PO3)3 grown oxide as the first layer and Al2O3 and MgF2 as the second and third layers respectively, so as to yield an overall theoretical reflectance of less than 2%. Since chemical oxides are readily grown on III-V semiconductors materials, the technique of using the grown oxide layer to both passivate the surface as well as serve as the first of a multilayer AR coating should work well for all III-V compound-based solar cells.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: Proceedings of the 14th Space Photovoltaic Research and Technology Conference (SPRAT 14); p 2
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  • 31
    Publication Date: 2019-01-25
    Description: High-efficiency, heteroepitaxial (HE) InP solar cells, grown on GaAs, Si or Ge substrates, are desirable for their mechanically strong, light-weight and radiation-hard properties. However, dislocations, caused by lattice mismatch, currently limit the performance of the HE cells. This occurs through shunting paths across the active photovoltaic junction and by the formation of deep levels. In previous work we have demonstrated that plasma hydrogenation is an effective and stable means to passivate the electrical activity of dislocations in specially designed HE InP test structures. In this work, we present the first report of successful hydrogen passivation in actual InP cell structures grown on GaAs substrates by metalorganic chemical vapor deposition (MOCVD). We have found that a 2 hour exposure to a 13.56 MHz hydrogen plasma at 275 C reduces the deep level concentration in HE n+n InP cell structures from as-grown values of approximately 10(exp 15)/cm(exp -3), down to 1-2 x 10(exp 13)/cm(exp -3). The deep levels in the p-type base region of the cell structure match those of our earlier p-type test structures, which were attributed to dislocations or related point defect complexes. All dopants were successfully reactivated by a 400 C, 5 minute anneal with no detectable activation of deep levels. I-V analysis indicated a subsequent approximately 10 fold decrease in reverse leakage current at -1 volt reverse bias, and no change in the forward biased series resistance of the cell structure which indicates complete reactivation of the n+ emitter. Furthermore, electrochemical C-V profiling indicates greatly enhanced passivation depth, and hence hydrogen diffusion, for heteroepitaxial structures when compared with identically processed homoepitaxial n+p InP structures. An analysis of hydrogen diffusion in dislocated InP will be discussed, along with comparisons of passivation effectiveness for n+p versus p+n heteroepitaxial cell configurations. Preliminary hydrogen-passivated HE InP cell results will also be presented.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Lewis Research Center, Proceedings of the 14th Space Photovoltaic Research and Technology Conference (SPRAT 14); p 21
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  • 32
    facet.materialart.
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    In:  Other Sources
    Publication Date: 2019-01-25
    Description: The first long-term (3000 hours) UV testing of unirradiated and 1 MeV electron-irradiated GaAs solar cells, with multilayer-coated coverslides to reduce solar array operating temperature, has produced some unexpected and important results. Two results, independent of the coverslide coatings, are of particular importance in terms of the predictability of GaAs solar-array lifetime in space: ( 1) The GaAs/Ge solar cells used for this series of tests displayed a much higher radiation degradation than that predicted based on JPL Solar Cell Radiation Handbook data. Covered cells degraded more in Isc than did bare cells. Short-term illumination at 60 C did not produce significant recovery (-1%) of the radiation damage. (2) However, electron radiation damage to these GaAs solar celIs anneals at 40 C when exposed to approximately 1 sun AM0 UV light sources for extended periods. The effect appears to be roughly linear with time (-1% of lsc per 1000 UVSH), is large (greater than or equal to 3%), and has not yet saturated (at 3000 hours). This photo-recovery of radiation damage to GaAs solar cells is a new effect and potentially important to the spacecraft community. The figure compares the effects of extended UV on irradiated and unirradiated GaAs solar cells with INTELSAT-6 Si cells. The effect and its generality, the extent of and conditions for photo-recovery, and the implications of such recovery for missions in radiation environments have not yet been determined.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Lewis Research Center, Proceedings of the 14th Space Photovoltaic Research and Technology Conference (SPRAT 14); p 17
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  • 33
    Publication Date: 2019-01-25
    Description: This proprietary technology is based on AstroPower's electrostatic bonding and innovative silicon solar cell processing techniques. Electrostatic bonding allows silicon wafers to be permanently attached to a thermally matched glass superstrate and then thinned to final thicknesses less than 25 micron. These devices are based on the features of a thin, light-trapping silicon solar cell: high voltage, high current, light weight (high specific power) and high radiation resistance. Monolithic interconnection allows the fabrication costs on a per watt basis to be roughly independent of the array size, power or voltage, therefore, the cost effectiveness to manufacture solar cell arrays with output powers ranging from milliwatts up to four watts and output voltages ranging from 5 to 500 volts will be similar. This compares favorably to conventionally manufactured, commercial solar cell arrays, where handling of small parts is very labor intensive and costly. In this way, a wide variety of product specifications can be met using the same fabrication techniques. Prototype solar cells have demonstrated efficiencies greater than 11%. An open-circuit voltage of 5.4 volts, fill factor of 65%, and short-circuit current density of 28 mA/sq cm at AM1.5 illumination are typical. Future efforts are being directed to optimization of the solar cell operating characteristics as well as production processing. The monolithic approach has a number of inherent advantages, including reduced cost per interconnect and increased reliability of array connections. These features make this proprietary technology an excellent candidate for a large number of consumer products.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Lewis Research Center, Proceedings of the 14th Space Photovoltaic Research and Technology Conference (SPRAT 14); p 19
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  • 34
    Publication Date: 2019-01-25
    Description: As part of a continuing program to determine the space radiation resistance of InP/ln(0.53)Ga(0.47)As tandem solar cells, n/p In(0.53)Ga(0. 47)As solar cells fabricated by RTI were irradiated with 1 MeV electrons and with 3 MeV protons. The cells were grown with a 3 micron n-lnP window layer to mimic the top cell in the tandem cell configuration for both AMO solar absorption and radiation effects. The results have been plotted against 'displacement damage dose' which is the product of the nonionizing energy loss (NIEL) and the particle fluence. A characteristic radiation damage curve can then be obtained for predicting the effect of all particles and energies. AMO, 1 sun solar illumination IV measurements were performed on the irradiated InGaAs solar cells and a characteristic radiation degradation curve was obtained using the solar cell conversion efficiency as the model parameter. Also presented are data comparing the radiation response of both n/p and p/n (fabricated by NREL) InGaAs solar cells as a function of base doping concentration. For the solar cell efficiency, the radiation degradation was found to be independent of the sample polarity for the same base doping concentration.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Lewis Research Center, Proceedings of the 14th Space Photovoltaic Research and Technology Conference (SPRAT 14); p 16
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  • 35
    Publication Date: 2019-01-25
    Description: Photovoltaic linear concentrator arrays can benefit from high performance solar cell technologies being developed at AstroPower. Specifically, these are the integration of thin GaAs solar cell and epitaxial lateral overgrowth technologies with the application of monolithically interconnected solar cell (MISC) techniques. This MISC array has several advantages which make it ideal for space concentrator systems. These are high system voltage, reliable low cost monolithically formed interconnections, design flexibility, costs that are independent of array voltage, and low power loss from shorts, opens, and impact damage. This concentrator solar cell will incorporate the benefits of light trapping by growing the device active layers over a low-cost, simple, PECVD deposited silicon/silicon dioxide Bragg reflector. The high voltage-low current output results in minimal 12R losses while properly designing the device allows for minimal shading and resistance losses. It is possible to obtain open circuit voltages as high as 67 volts/cm of solar cell length with existing technology. The projected power density for the high performance device is 5 kW/m for an AMO efficiency of 26% at 1 5X. Concentrator solar cell arrays are necessary to meet the power requirements of specific mission platforms and can supply high voltage power for electric propulsion systems. It is anticipated that the high efficiency, GaAs monolithically interconnected linear concentrator solar cell array will enjoy widespread application for space based solar power needs. Additional applications include remote man-portable or ultra-light unmanned air vehicle (UAV) power supplies where high power per area, high radiation hardness and a high bus voltage or low bus current are important. The monolithic approach has a number of inherent advantages, including reduced cost per interconnect and increased reliability of array connections. There is also a high potential for a large number of consumer products. Dual-use applications can include battery chargers and remote power supplies for consumer electronics products such as portable telephones/beepers, portable radios, CD players, dashboard radar detectors, remote walkway lighting, etc.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Lewis Research Center, Proceedings of the 14th Space Photovoltaic Research and Technology Conference (SPRAT 14); p 20
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  • 36
    Publication Date: 2019-01-25
    Description: Indium phosphide (InP) solar cells are being made on silicon (Si) wafers (InP/Si) to take advantage of both the radiation-hardness properties of the InP solar cell and the light weight and low cost of Si wafers compared to InP or germanium (Ge) wafers. The InP/Si cell application is for long duration and/or high radiation orbit space missions. InP/Si cells have higher absolute efficiency after a high radiation dose than gallium arsenide (GaAs) or silicon (Si) solar cells. In this work, base electron diffusion lengths in the N/P cell are extracted from measured AM0 short-circuit photocurrent at various irradiation levels out to an equivalent 1 MeV fluence of 1017 1 MeV electrons/sq cm for a 1 sq cm 12% BOL InP/Si cell. These values are then checked for consistency by comparing measured Voc data with a theoretical Voc model that includes a dark current term that depends on the extracted diffusion lengths.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Lewis Research Center, Proceedings of the 14th Space Photovoltaic Research and Technology Conference (SPRAT 14); p 15
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  • 37
    Publication Date: 2019-01-25
    Description: An analysis embodied in a PC computer program is presented which quantitatively demonstrates how the availability of radiation hard solar cells can minimize the cost of a global satellite communication system. The chief distinction between the currently proposed systems, such as Iridium Odyssey and Ellipsat, is the number of satellites employed and their operating altitudes. Analysis of the major costs associated with implementing these systems shows that operation within the earth's radiation belts can reduce the total system cost by as much as a factor of two, so long as radiation hard components including solar cells, can be used. A detailed evaluation of several types of planar solar cells is given, including commercially available Si and GaAs/Ge cells, and InP/Si cells which are under development. The computer program calculates the end of life (EOL) power density of solar arrays taking into account the cell geometry, coverglass thickness, support frame, electrical interconnects, etc. The EOL power density can be determined for any altitude from low earth orbit (LEO) to geosynchronous (GEO) and for equatorial to polar planes of inclination. The mission duration can be varied over the entire range planned for the proposed satellite systems. An algorithm is included in the program for determining the degradation of cell efficiency for different cell technologies due to proton and electron irradiation. The program can be used to determine the optimum configuration for any cell technology for a particular orbit and for a specified mission life. Several examples of applying the program are presented, in which it is shown that the EOL power density of different technologies can vary by an order of magnitude for certain missions. Therefore, although a relatively radiation soft technology can be made to provide the required EOL power by simply increasing the size of the array, the impact on the total system budget could be unacceptable, due to increased launch and hardware costs. In aggregate these factors can account for more than a 10% increase in the total system cost. Since the estimated total costs of proposed global coverage systems range from $1 Billion to $9 Billion, the availability of radiation hard solar cells could make a decisive difference in the selection of a particular constellation architecture.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Lewis Research Center, Proceedings of the 14th Space Photovoltaic Research and Technology Conference (SPRAT 14); p 12
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  • 38
    Publication Date: 2019-01-25
    Description: Multi-junction (MJ), gallium arsenide (GaAs), and silicon (Si) solar cells have respective test efficiencies of approximately 24%, 18.5% and 14.8%. Multi-junction and gallium arsenide solar cells weigh more than silicon solar cells and cost approximately five times as much per unit power at the cell level. A straw man trade is performed for the TRMM spacecraft to determine which of these cell types would have offered an overall performance and price advantage to the spacecraft. A straw man trade is also performed for the multi-junction cells under the assumption that they will cost over ten times that of silicon cells at the cell level. The trade shows that the TRMM project, less the cost of the instrument, ground systems and mission operations, would spend approximately $552 thousand dollars per kilogram to launch and service science in the case of the spacecraft equipped with silicon solar cells. If these cells are changed out for gallium arsenide solar cells, an additional 31 kilograms of science can be launched and serviced at a price of approximately $90 thousand per kilogram. The weight reduction is shown to derive from the smaller area of the array and hence reductions in the weight of the array substrate and supporting structure. If the silicon solar cells are changed out for multi-junction solar cells, an additional 45 kilograms of science above the silicon base line can be launched and serviced at a price of approximately $58 thousand per kilogram. The trade shows that even if the multi-junction arrays are priced over ten times that of silicon cells, a price that is much higher than projected, that the additional 45 kilograms of science are launched and serviced at $182 thousand per kilogram. This is still much less than original $552 thousand per kilogram to launch and service the science. Data and qualitative factors are presented to show that these figures are subject to a great deal of uncertainty. Nonetheless, the benefit of the higher efficiency solar cells for TRMM is far greater than the uncertainties in the analysis.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Lewis Research Center, Proceedings of the 14th Space Photovoltaic Research and Technology Conference (SPRAT 14); p 8
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  • 39
    Publication Date: 2019-01-25
    Description: In this paper we report the successful fabrication of large area, monolithic triple junction, n on p, GaInP2/GaAs/Ge cells. The highest open circuit voltage and cell efficiency (cell area: 4.078 sq cm) were measured at 2.573 V and 23.3%, respectively, under 1 sun, AMO illumination. To our knowledge, this is the highest single crystal, monolithic, two terminal triple junction cell efficiency demonstrated. In addition, excellent uniformity across a 3 inch diameter Ge substrates has also been achieved. An average cell efficiency of 22.8% across the 3 inch diameter wafer has been measured. We have also successfully fabricated welded cell-interconnect-cover (CIC) assemblies using these triple junction devices. The highest CIC efficiency was 23.2% (bare cell efficiency was 23.3%). The average efficiency for 25 CICs was 21.8%, which is very comparable to the 22.0% average bare cell efficiency before they were fabricated into the CICs. Finally, we have measured temperature coefficient and 1 MeV electron irradiation data. These will be presented in the paper.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Lewis Research Center, Proceedings of the 14th Space Photovoltaic Research and Technology Conference (SPRAT 14); p 9
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  • 40
    facet.materialart.
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    Publication Date: 2019-01-25
    Description: Energy storage and production in space requires rugged, reliable hardware which minimizes weight, volume, and maintenance while maximizing power output and usable energy storage. These systems generally consist of photovoltaic solar arrays which operate during sunlight cycles to provide system power and regenerate fuel (hydrogen) via water electrolysis; during dark cycles, hydrogen is converted by the fuel cell into system. The currently preferred configuration uses two separate systems (fuel cell and electrolyzer) in conjunction with photovoltaic cells. Fuel cell/electrolyzer system simplicity, reliability, and power-to-weight and power-to-volume ratios could be greatly improved if both power production (fuel cell) and power storage (electrolysis) functions can be integrated into a single unit. The Technology Management, Inc. (TMI), solid oxide fuel cell-based system offers the opportunity to both integrate fuel cell and electrolyzer functions into one unit and potentially simplify system requirements. Based an the TMI solid oxide fuel cell (SOPC) technology, the TMI integrated fuel cell/electrolyzer utilizes innovative gas storage and operational concepts and operates like a rechargeable 'hydrogen-oxygen battery'. Preliminary research has been completed on improved H2/H2O electrode (SOFC anode/electrolyzer cathode) materials for solid oxide, regenerative fuel cells. Improved H2/H2O electrode materials showed improved cell performance in both fuel cell and electrolysis modes in reversible cell tests. ln reversible fuel cell/electrolyzer mode, regenerative fuel cell efficiencies (ratio of power out (fuel cell mode) to power in (electrolyzer model)) improved from 50 percent (using conventional electrode materials) to over 80 percent. The new materials will allow the TMI SOFC system to operate as both the electrolyzer and fuel cell in a single unit. Preliminary system designs have also been developed which indicate the technical feasibility of using the TMI SOFC technology for space applications with high energy storage efficiencies and high specific energy. Development of small space systems would also have potential dual-use, terrestrial applications.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Lewis Research Center, Space Electrochemical Research and Technology. Abstracts; p 25
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  • 41
    Publication Date: 2019-01-25
    Description: A difficulty encountered in designing a unitized regenerative proton exchange membrane (PEM) fuel cell lies in the incompatibility of electrode structures and electrocatalyst materials optimized for either of the two functions (fuel cell or electrolyzer) with the needs of the other function. This difficulty is compounded in previous regenerative fuel cell designs by the fact that water, which is needed for proton conduction in the PEM during both modes of operation, is the reactant supplied to the anode in the electrolyzer mode of operation and the product formed at the cathode in the fuel cell mode. Drawbacks associated with existing regenerative fuel cells have been addressed in work performed at Lynntech. In a first innovation, electrodes function either as oxidation electrodes (hydrogen ionization or oxygen evolution) or as reduction electrodes (oxygen reduction or hydrogen evolution) in the fuel cell and electrolyzer modes, respectively. Control of liquid water within the regenerative fuel cell has been brought about by a second innovation. A novel PEM has been developed with internal channels that permit the direct access of water along the length of the membrane. Lateral diffusion of water along the polymer chains of the PEM provides the water needed at electrode/PEM interfaces. Fabrication of the novel unitized regenerative fuel cell and results obtained on testing it will be presented.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Lewis Research Center, Space Electrochemical Research and Technology. Abstracts; p 21
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  • 42
    Publication Date: 2019-06-28
    Description: A direct numerical simulation (DNS) algorithm has been developed and validated for use in the investigation of crossflow instability on supersonic swept wings, an application of potential relevance to the design of the High-Speed Civil Transport (HSCT). The algorithm is applied to the investigation of stationary crossflow instability on an infinitely long 77-degree swept wing in Mach 3.5 flow. The results of the DNS are compared with the predictions of linear parabolized stability equation (PSE) methodology. In-general, the DNS and PSE results agree closely in terms of modal growth rate, structure, and orientation angle. Although further validation is needed for large-amplitude (nonlinear) disturbances, the close agreement between independently derived methods offers preliminary validation of both DNS and PSE approaches.
    Keywords: AERODYNAMICS
    Type: NASA-CR-198267 , NAS 1.26:198267 , NIPS-96-08486
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  • 43
    Publication Date: 2019-06-28
    Description: Two F-18 aircraft were flown, one above the other, in two formations, in order for the shock systems of the two aircraft to merge and propagate to the ground. The first formation had the canopy of the lower F-18 in the inlet shock of the upper F-18 (called inlet-canopy). The flight conditions were Mach 1.22 and an altitude of 23,500 ft. An array of five sonic boom recorders was used on the ground to record the sonic boom signatures. This paper describes the flight test technique and the ground level sonic boom signatures. The tail-canopy formation resulted in two, separated, N-wave signatures. Such signatures probably resulted from aircraft positioning error. The inlet-canopy formation yielded a single modified signature; two recorders measured an approximate flattop signature. Loudness calculations indicated that the single inlet-canopy signatures were quieter than the two, separated tail-canopy signatures. Significant loudness occurs after a sonic boom signature. Such loudness probably comes from the aircraft engines.
    Keywords: AERODYNAMICS
    Type: NASA-TM-104312 , H-2067 , NAS 1.15:104312
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  • 44
    Publication Date: 2019-06-28
    Description: A multiblock, discrete sensitivity analysis method is used to couple a direct optimization method and a flow analysis method. The domain is divided into smaller subdomains for which the sensitivities are obtained separately. Then, an effective sensitivity equation is solved to complete the coupling of all the sensitivity information. The flow analysis is based on the thin-layer Navier-Stokes equations solved by an implicit, upwind-biased, finite-volume method. The method of feasible directions is used for the present gradient-based optimization approach. First, a transonic airfoil is optimized to investigate the behavior of the method in highly nonlinear flows as well as the effect of different blocking strategies on the procedure. A supercritical airfoil is produced from an initially symmetric airfoil with multiblocking affecting the path but not the final shape. Secondly, a two-element airfoil is shape optimized in subsonic flow to demonstrate the present method's capability of shaping aerodynamically interfering elements simultaneously. For a very low and a very high Reynolds number cases, the shape of the main airfoil and the flap are optimized to yield improved lift-to-drag ratios.
    Keywords: AERODYNAMICS
    Type: NASA-CR-199785 , NAS 1.26:199785 , AIAA PAPER 94-4273 , NIPS-95-06444
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  • 45
    Publication Date: 2019-06-28
    Description: This report summarizes some NASA Lewis (i.e., government owned) computer codes capable of being used for airbreathing propulsion system studies to determine the design geometry and to predict the design/off-design performance of compressors and turbines. These are not CFD codes; velocity-diagram energy and continuity computations are performed fore and aft of the blade rows using meanline, spanline, or streamline analyses. Losses are provided by empirical methods. Both axial-flow and radial-flow configurations are included.
    Keywords: AERODYNAMICS
    Type: NASA-CR-198433 , NAS 1.26:198433 , E-10041 , NIPS-95-06493
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  • 46
    Publication Date: 2019-06-28
    Description: Chemical beam epitaxy (CBE) has been shown to allow the growth of high quality materials with reproducible complex compositional and doping profiles. The main advantage of CBE compared to metalorganic chemical vapor deposition (MOCVD), the most popular technique for InP-based photovoltaic device fabrication, is the ability to grow high purity epilayers at much lower temperatures (450-530 C). We have previously shown that CBE is perfectly suited toward the fabrication of complex photovoltaic devices such as InP/InGaAs monolithically integrated tandem solar cells, because its low process temperature preserves the electrical characteristics of the InGaAs tunnel junction commonly used as an ohmic interconnect. In this work using CBE for the fabrication of optically transparent (with respect to the bottom cell) InP tunnel diodes is demonstrated. Epitaxial growth were performed in a Riber CBE 32 system using PH3 and TMIn as III and V precursors. Solid Be (p-type) and Si (n-type) have been used as doping sources, allowing doping levels up to 2 x 10(exp -19)/cu cm and 1 x 10(exp -19)/cu cm for n and p type respectively. The InP tunnel junction characteristics and the influence of the growth's conditions (temperature, growth rate) over its performance have been carefully investigated. InP p(++)/n(++) tunnel junction with peak current densities up to 1600 A/sq cm and maximum specific resistivities (V(sub p)/I(sub p) - peak voltage to peak current ratio) in the range of 10(exp -4) Omega-sq cm were obtained. The obtained peak current densities exceed the highest results previously reported for their lattice matched counterparts, In(0.53)Ga( 0.47)As and should allow the realization of improved minimal absorption losses in the interconnect InP/InGaAs tandem devices for Space applications. Owing to the low process temperature required for the top cell, these devices exhibit almost no degradation of its characteristics after the growth of subsequent thick InP layer suggesting minimal doping cross diffusion in the narrow space-charge region (approximately 1-5 nm) of the device. The fabrication of tandem devices using InP tunnel diodes as interconnect is in progress and will be reported at the conference.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Lewis Research Center, Proceedings of the 14th Space Photovoltaic Research and Technology Conference (SPRAT 14); p 11
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  • 47
    Publication Date: 2019-06-28
    Description: A far-wing theory in which the validity of the detailed balance principle is maintained in each step of the derivation is presented. The role of the total density matrix including the initial correlations is analyzed rigorously. By factoring out the rapidly varying terms in the complex-time development operator in the interaction representation, better approximate expressions can be obtained. As a result, the spectral density can be expressed in terms of the line-coupling functions in which two coupled lines are arranged symmetrically and whose frequency detunings are omega - 1/2(omega(sub ji) + omega (sub j'i'). Using the approximate values omega - omega(sub ji) results in expressions that do not satisfy the detailed balance principle. However, this principle remains satisfied for the symmetrized spectral density in which not only the coupled lines are arranged symmetrically, but also the initial and final states belonging to the same lines are arranged symmetrically as well.
    Keywords: AERODYNAMICS
    Type: NASA-TM-111075 , NAS 1.15:111075
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  • 48
    Publication Date: 2019-06-28
    Description: To identify planform characteristics which have promise for a highly maneuverable vehicle, an investigation was conducted in the Langley Subsonic Basic Research Tunnel to determine the low-speed longitudinal aerodynamics of 21 planform geometries. Concepts studied included twin bodies, double wings, cutout wings, and serrated forebodies. The planform models tested were all 1/4-in.-thick flat plates with beveled edges on the lower surface to ensure uniform flow separation at angle of attack. A 1.0-in.-diameter cylindrical metric body with a hemispherical nose was used to house the six-component strain gauge balance for each configuration. Aerodynamic force and moment data were obtained across an angle-of-attack range of 0 to 70 deg with zero sideslip at a free-stream dynamic pressure of 30 psf. Surface flow visualization studies were also conducted on selected configurations using fluorescent minitufts. Results from the investigation indicate that a cutout wing planform can improve lift characteristics; however, cutout size, shape, and position and wing leading-edge sweep will all influence the effectiveness of the cutout configuration. Tests of serrated forebodies identified this concept as an extremely effective means of improving configuration lift characteristics; increases of up to 25 percent in the value of maximum lift coefficient were obtained.
    Keywords: AERODYNAMICS
    Type: NASA-TP-3503 , L-17301 , NAS 1.60:3503
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  • 49
    Publication Date: 2019-06-28
    Description: The computational fluid dynamics code, PARC3D, is tested to see if its use of non-physical artificial dissipation affects the accuracy of its results. This is accomplished by simulating a shock-laminar boundary layer interaction and several hypersonic flight conditions of the Pegasus(TM) launch vehicle using full artificial dissipation, low artificial dissipation, and the Engquist filter. Before the filter is applied to the PARC3D code, it is validated in one-dimensional and two-dimensional form in a MacCormack scheme against the Riemann and convergent duct problem. For this explicit scheme, the filter shows great improvements in accuracy and computational time as opposed to the nonfiltered solutions. However, for the implicit PARC3D code it is found that the best estimate of the Pegasus experimental heat fluxes and surface pressures is the simulation utilizing low artificial dissipation and no filter. The filter does improve accuracy over the artificially dissipative case but at a computational expense greater than that achieved by the low artificial dissipation case which has no computational time penalty and shows better results. For the shock-boundary layer simulation, the filter does well in terms of accuracy for a strong impingement shock but not as well for weaker shock strengths. Furthermore, for the latter problem the filter reduces the required computational time to convergence by 18.7 percent.
    Keywords: AERODYNAMICS
    Type: NASA-CR-186033 , H-2071 , NAS 1.26:186033
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  • 50
    Publication Date: 2019-06-28
    Description: An optimization procedure is developed for the simultaneous improvement of the aerodynamic and sonic boom characteristics of high speed aircraft. From a sonic boom perspective, it is desirable to minimize the first peak in the overpressure signal at a specified distance away from the aircraft. From aerodynamic point of view, the aerodynamic drag coefficient ratio must be minimized while maintaining the lift coefficient at desired level. The optimization procedure is applied to wing-body configurations related to high speed aircraft. The objectives of this current research are: (1) development of a multiobjective optimization procedure for aerospace vehicles with the integration of sonic boom and aerodynamic performance criteria; and (2) development of semi-analytical approach for calculating sonic boom design sensitivities.
    Keywords: AERODYNAMICS
    Type: NASA-CR-199083 , NAS 1.26:199083
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  • 51
    Publication Date: 2019-06-28
    Description: During the Higher Harmonic Control Aeroacoustic Rotor Test, extensive measurements of the rotor aerodynamics, the far-field acoustics, the wake geometry, and the blade motion for powered, descent, flight conditions were made. These measurements have been used to validate and improve the prediction of blade-vortex interaction (BVI) noise. The improvements made to the BVI modeling after the evaluation of the test data are discussed. The effects of these improvements on the acoustic-pressure predictions are shown. These improvements include restructuring the wake, modifying the core size, incorporating the measured blade motion into the calculations, and attempting to improve the dynamic blade response. A comparison of four different implementations of the Ffowcs Williams and Hawkings equation is presented. A common set of aerodynamic input has been used for this comparison.
    Keywords: AERODYNAMICS
    Type: NASA-TM-110825 , NAS 1.15:110825 , AD-A294477
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  • 52
    Publication Date: 2019-06-28
    Description: An extensive quantity of airload measurements was obtained for a pressure-instrumented model of the BO-105 main rotor for a large number of higher-harmonic control (HHC) settings at Duits-Nederlandse Wind Tunnel (DNW). The wake geometry, vortex strength, and vortex core size were also measured through a laser light sheet technique and LDV. These results are used to verify the BVI airload prediction methodologies developed by AFDD, DLR, NASA Langley, and ONERA. The comparisons show that an accurate prediction of the blade motion and the wake geometry is the most important aspect of the BVI airload predictions.
    Keywords: AERODYNAMICS
    Type: NASA-TM-110824 , NAS 1.15:110824 , AD-A294468
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  • 53
    Publication Date: 2019-06-28
    Description: This is a guide for the use of the pressure disk rotor model that has been placed in the incompressible Navier-Stokes code INS3D-UP. The pressure disk rotor model approximates a helicopter rotor or propeller in a time averaged manner and is intended to simulate the effect of a rotor in forward flight on the fuselage or the effect of a propeller on other aerodynamic components. The model uses a modified actuator disk that allows the pressure jump across the disk to vary with radius and azimuth. The cyclic and collective blade pitch angles needed to achieve a specified thrust coefficient and zero moment about the hub are predicted. The method has been validated with experimentally measured mean induced inflow velocities as well as surface pressures on a generic fuselage. Overset grids, sometimes referred to as Chimera grids, are used to simplify the grid generation process. The pressure disk model is applied to a cylindrical grid which is embedded in the grid or grids used for the rest of the configuration. This document will outline the development of the method, and present input and results for a sample case.
    Keywords: AERODYNAMICS
    Type: NASA-CR-4692 , NAS 1.26:4692
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  • 54
    Publication Date: 2019-06-28
    Description: Future hypersonic vehicles are going to be designed largely with computational fluid dynamic methods based on appropriate physical models. The question on how much of this design process can be completed with the present state of computational aerothermodynamics is addressed. Some limitations of current models are discussed. It is shown that much more research is required before it will be possible to accurately design a hypersonic vehicle for all of its flight conditions. The quantities that must be computed accurately so that a minimum weight hypersonic vehicle can be designed are discussed. The use of computational fluid dynamics methods coupled with current thermochemical models in order to compute the quantities under specific flow conditions is considered.
    Keywords: AERODYNAMICS
    Type: ESA, Proceedings of the 2nd European Symposium on Aerothermodynamics for Space Vehicles; p 365-37
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  • 55
    Publication Date: 2019-06-28
    Description: An experimental investigation was conducted to determine the aerodynamic characteristics of a store as it was separated from the lee side of a flat plate inclined at 15 deg to the free-stream flow at Mach 6. Two store models were tested: a cone cylinder and a roof delta. Force and moment data were obtained for both stores as they were moved in 0.5-in. increments away from the flat plate lee-side separated flow region into the free-stream flow while the store angle of attack was held constant at either 0 deg or 15 deg. The results indicate that both stores had adverse separation characteristics (i.e., negative normal force and pitching moment) at an angle of attack of 0 deg, and the cone cylinder had favorable separation characteristics (i.e., positive normal force and pitching moment) at an angle of attack of 15 deg. At an angle of attack of 15 deg, the separation characteristics of the roof delta are indeterminate at small separation distances and favorable at greater separation distances. These characteristics are the result of the local flow inclination relative to the stores as they traversed through the flat plate lee-side flow field. In addition to plotted data, force and moment data are tabulated and schlieren photographs of the stores and flat plate are presented.
    Keywords: AERODYNAMICS
    Type: NASA-TM-4652 , L-17384 , NAS 1.15:4652
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  • 56
    Publication Date: 2019-06-28
    Description: A high Reynolds number investigation of a commercial transport model was conducted in the National Transonic Facility (NTF) at Langley Research Center. This investigation was part of a cooperative effort to test a 0.03-scale model of a Boeing 767 airplane in the NTF over a Mach number range of 0.70 to 0.86 and a Reynolds number range of 2.38 to 40.0 x 10(exp 6) based on the mean aerodynamic chord. One of several specific objectives of the current investigation was to evaluate the level of data repeatability attainable in the NTF. Data repeatability studies were performed at a Mach number of 0.80 with Reynolds numbers of 2.38, 4.45, and 40.0 x 10(exp 6) and also at a Mach number of 0.70 with a Reynolds number of 40.0 x 10(exp 6). Many test procedures and data corrections are addressed in this report, but the data presented do not include corrections for wall interference, model support interference, or model aeroelastic effects. Application of corrections for these three effects would not affect the results of this study because the corrections are systematic in nature and are more appropriately classified as sources of bias error. The repeatability of the longitudinal stability-axis force and moment data has been accessed. Coefficients of lift, drag, and pitching moment are shown to repeat well within the pretest goals of plus or minus 0.005, plus or minus 0.0001, and plus or minus 0.001, respectively, at a 95-percent confidence level over both short- and near-term periods.
    Keywords: AERODYNAMICS
    Type: NASA-TP-3522 , L-17412 , NAS 1.60:3522
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  • 57
    Publication Date: 2019-06-28
    Description: An experimental investigation was conducted to determine the effect of diverter wedge half-angle and nacelle lip height on the drag characteristics of an assembly consisting of a nacelle fore cowl from a typical high-speed civil transport (HSCT) and a diverter mounted on a flat plate. Data were obtained for diverter wedge half-angles of 4.0 deg, 6.0 deg, and 8.0 deg and ratios of the nacelle lip height above a flat plate to the boundary-layer thickness (h(sub n)/delta) of approximately 0.87 to 2.45. Limited drag data were also obtained on a complete nacelle/diverter configuration that included fore and aft cowls. Although the nacelle/diverter drag data were not corrected for base pressures or internal flow drag, the data are useful for comparing the relative drag of the configuration tested. The tests were conducted in the Langley Unitary Plan Wind Tunnel at Mach numbers of 1.50, 1.80, 2.10, and 2.40 and Reynolds numbers ranging from 2.00 x 10(exp 6) to 5.00 x 10(exp 6) per foot. The results of this investigation showed that the nacelle/diverter drag essentially increased linearly with increasing h(sub n)/delta except near 1.0 where the data showed a nonlinear behavior. This nonlinear behavior was probably caused by the interaction of the shock waves from the nacelle/diverter configuration with the flat-plate boundary layer. At the lowest h(sub n)/delta tested, the diverter wedge half-angle had virtually no effect on the nacelle/diverter drag. However, as h(sub n)/delta increased, the nacelle/diverter drag increased as diverter wedge half-angle increased.
    Keywords: AERODYNAMICS
    Type: NASA-TM-4660 , L-17416 , NAS 1.15:4660
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  • 58
    Publication Date: 2019-06-28
    Description: Water droplet trajectories within the NASA Lewis Research Center's Icing Research Tunnel (IRT) were studied through computer analysis. Of interest was the influence of the wind tunnel contraction and wind tunnel model blockage on the water droplet trajectories. The computer analysis was carried out with a program package consisting of a three-dimensional potential panel code and a three-dimensional droplet trajectory code. The wind tunnel contraction was found to influence the droplet size distribution and liquid water content distribution across the test section from that at the inlet. The wind tunnel walls were found to have negligible influence upon the impingement of water droplets upon a wing model.
    Keywords: AERODYNAMICS
    Type: NASA-TM-107023 , E-9828 , NAS 1.15:107023
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  • 59
    facet.materialart.
    Unknown
    In:  CASI
    Publication Date: 2019-06-28
    Description: This document outlines the tests performed to make aerodynamic force and torque measurements on the SOFIA wind tunnel model telescope. These tests were performed during the SOFIA 2 wind tunnel test in the 14 ft wind tunnel during the months of June through August 1994. The test was designed to measure the dynamic cross elevation moment acting on the SOFIA model telescope due to aerodynamic loading. The measurements were taken with the telescope mounted in an open cavity in the tail section of the SOFIA model 747. The purpose of the test was to obtain an estimate of the full scale aerodynamic disturbance spectrum, by scaling up the wind tunnel results (taking into account differences in sail area, air density, cavity dimension, etc.). An estimate of the full scale cross elevation moment spectrum was needed to help determine the impact this disturbance would have on the telescope positioning system requirements. A model of the telescope structure, made of a light weight composite material, was mounted in the open cavity of the SOFIA wind tunnel model. This model was mounted via a force balance to the cavity bulkhead. Despite efforts to use a 'stiff' balance, and a lightweight model, the balance/telescope system had a very low resonant frequency (37 Hz) compared to the desired measurement bandwidth (1000 Hz). Due to this mechanical resonance of the balance/telescope system, the balance alone could not provide an accurate measure of applied aerodynamic force at the high frequencies desired. A method of measurement was developed that incorporated accelerometers in addition to the balance signal, to calculate the aerodynamic force.
    Keywords: AERODYNAMICS
    Type: NASA-TM-110668 , SER-PK-001 , NAS 1.15:110668
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  • 60
    Publication Date: 2019-06-28
    Description: The work reported here pertains only to the first year of research for a three year proposal period. As a prelude to this two dimensional interface element, the one dimensional element was tested and errors were discovered in the code for built-up structures and curved interfaces. These errors were corrected and the benchmark Boeing composite crown panel was analyzed successfully. A study of various splines led to the conclusion that cubic B-splines best suit this interface element application. A least squares approach combined with cubic B-splines was constructed to make a smooth function from the noisy data obtained with random error in the coordinate data points of the Boeing crown panel analysis. Preliminary investigations for the formulation of discontinuous 2-D shell and 3-D solid elements were conducted.
    Keywords: AERODYNAMICS
    Type: NASA-CR-199951 , NAS 1.26:199951 , NIPS-96-07072
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  • 61
    Publication Date: 2019-06-28
    Description: Test flights were conducted to evaluate the capability of Differential Global Positioning System (DGPS) to provide the accuracy and integrity required for International Civil Aviation Organization (ICAO) Category (CAT) III precision approach and landings. These test flights were part of a Federal Aviation Administration (FAA) program to evaluate the technical feasibility of using DGPS based technology for CAT III precision approach and landing applications. An IAI Westwind 1124 aircraft (N24RH) was equipped with DGPS receiving equipment and additional computing capability provided by E-Systems. The test flights were conducted at NASA Ames Research Center's Crows Landing Flight Facility, Crows Landing, California. The flight test evaluation was based on completing 100 approaches and landings. The navigation sensor error accuracy requirements were based on ICAO requirements for the Microwave Landing System (MLS). All of the approaches and landings were evaluated against ground truth reference data provided by a laser tracker. Analysis of these approaches and landings shows that the E-Systems DGPS system met the navigation sensor error requirements for a successful approach and landing 98 out of 100 approaches and landings, based on the requirements specified in the FAA CAT III Level 2 Flight Test Plan. In addition, the E-Systems DGPS system met the integrity requirements for a successful approach and landing or stationary trial for all 100 approaches and landings and all ten stationary trials, based on the requirements specified in the FAA CAT III Level 2 Flight Test Plan.
    Keywords: AERODYNAMICS
    Type: NASA-TM-110368 , NAS 1.15:110368 , A-950096
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  • 62
    Publication Date: 2019-06-28
    Description: This monograph provides an extensive list of formulas for airfoil polynomials. These polynomials provide convenient expansion functions for the description of the downwash and pressure distributions of linear theory for airfoils in both steady and unsteady subsonic flow.
    Keywords: AERODYNAMICS
    Type: NASA-RP-1343 , L-17420 , NAS 1.61:1343
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  • 63
    Publication Date: 2019-06-28
    Description: Low-speed wind-tunnel tests were conducted in the Langley 12-Foot Low-Speed Tunnel on a model of the Boeing Multirole Fighter (BMRF) aircraft. This single-seat, single-engine configuration was intended to be an F-16 replacement that would incorporate many of the design goals and advanced technologies of the F-22. Its mission requirements included supersonic cruise without afterburner, reduced observability, and the ability to attack both air-to-air and air-to-ground targets. So that it would be effective in all phases of air combat, the ability to maneuver at angles of attack up to and beyond maximum lift was also desired. Traditional aerodynamic yaw controls, such as rudders, are typically ineffective at these higher angles of attack because they are usually located in the wake from the wings and fuselage. For this reason, this study focused on investigating forebody-mounted controls that produces yawing moments by modifying the strong vortex flowfield being shed from the forebody at high angles of attack. Two forebody strakes were tested that varied in planform and chordwise location. Various patterns of porosity in the forebody skin were also tested that differed in their radial coverage and chordwise location. The tests were performed at a dynamic pressure of 4 lb/ft(exp 2) over an angle-of-attack range of -4 deg to 72 deg and a sideslip range of -10 deg to 10 deg. Static force data, static pressures on the surface of the forebody, and videotapes of flow-visualization using laser-illuminated smoke were obtained.
    Keywords: AERODYNAMICS
    Type: NASA-CR-4685 , NAS 1.26:4685
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  • 64
    facet.materialart.
    Unknown
    In:  CASI
    Publication Date: 2019-06-28
    Description: This paper presents an overview of the complex unsteady vortical flows that comprise the wakes of rotary-wing aircraft; of the effects these tangled vortical structures have on the performance, noise, and vibration; and of some of the recent attempts to measure, predict, and control the phenomena. The main points are illustrated with a number of examples from the recent literature and technical conferences.
    Keywords: AERODYNAMICS
    Type: NASA-TM-110822 , NAS 1.15:110822 , AD-A294465
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  • 65
    Publication Date: 2019-06-28
    Description: An unswept, semispan wing model incorporating a NACA 0012 airfoil section was tested in the Langley 14- by 22-Foot Subsonic Tunnel. This report contains pressure data which document effects of wing configuration and free-stream conditions on wing pressure distributions. The untwisted wing incorporated a full-span, leading-edge Krueger flap and a full-span, single-slotted trailing-edge flap. The trailing-edge flap was tested at a deflection angle of 40 degrees and the Krueger flap at a deflection of 55 degrees. Three wing configurations were tested: cruise, trailing-edge flap only, and Knueger flap and trailing-edge flap deployed. Tests were conducted at free-stream dynamic pressures of 15, 30 and 60 psf, with corresponding chord Reynolds numbers of 1.22 to 2.11 million and Mach numbers of 0.12 to 0.20. Angles of attack presented range from 0 to 20 degrees, depending on wing configuration. The data are presented without analysis.
    Keywords: AERODYNAMICS
    Type: NASA-TM-110148 , NAS 1.15:110148
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  • 66
    Publication Date: 2019-06-28
    Description: This report addresses the development of a multidisciplinary optimization procedure using an efficient semi-analytical sensitivity analysis technique and multilevel decomposition for the design of aerospace vehicles. A semi-analytical sensitivity analysis procedure is developed for calculating computational grid sensitivities and aerodynamic design sensitivities. Accuracy and efficiency of the sensitivity analysis procedure is established through comparison of the results with those obtained using a finite difference technique. The developed sensitivity analysis technique are then used within a multidisciplinary optimization procedure for designing aerospace vehicles. The optimization problem, with the integration of aerodynamics and structures, is decomposed into two levels. Optimization is performed for improved aerodynamic performance at the first level and improved structural performance at the second level. Aerodynamic analysis is performed by solving the three-dimensional parabolized Navier Stokes equations. A nonlinear programming technique and an approximate analysis procedure are used for optimization. The proceduredeveloped is applied to design the wing of a high speed aircraft. Results obtained show significant improvements in the aircraft aerodynamic and structural performance when compared to a reference or baseline configuration. The use of the semi-analytical sensitivity technique provides significant computational savings.
    Keywords: AERODYNAMICS
    Type: NASA-CR-199290 , NAS 1.26:199290
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  • 67
    Publication Date: 2019-06-28
    Description: The effectiveness of steady and pulsed blowing as a method of controlling delta wing vortices during ramp pitching has been investigated in flow visualization experiments conducted in a water tunnel. The recessed angled spanwise blowing technique was utilized for vortex manipulation. This technique was implemented on a beveled 60 delta wing using a pair of blowing ports located beneath the vortex core at 40% chord. The flow was injected primarily in the spanwise direction but was also composed of a component normal to the wing surface. The location of vortex burst was measured as a function of blowing intensity and pulsing frequency under static conditions, and the optimum blowing case was applied at three different wing pitching rates. Experimental results have shown that, when the burst location is upstream of the blowing port, pulsed blowing delays vortex breakdown in static and dynamic cases. Dynamic tests verified the existence of a hysteresis effect and demonstrated the improvements offered by pulsed blowing over both steady blowing and no-blowing scenarios. The application of blowing, at the optimum pulsing frequency, made the vortex breakdown location comparable in static and ramp pitch-up conditions.
    Keywords: AERODYNAMICS
    Type: NIPS-95-05494 , NASA-CR-199624 , NAS 1.26:199624 , AIAA PAPER 95-1817-CP , United States
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  • 68
    Publication Date: 2019-06-28
    Description: Primarily an experimental effort, this study focuses on the velocity and vorticity fields in the near wake of a hovering rotor. Drag terminology is reviewed, and the theory for separately determining the profile-and-induced-drag components from wake quantities is introduced. Instantaneous visualizations of the flow field are used to center the laser velocimeter (LV) measurements on the vortex core and to assess the extent of the positional mandering of the trailing vortex. Velocity profiles obtained at different rotor speeds and distances behind the rotor blade clearly indicate the position, size, and rate of movement of the wake sheet and the core of the trailing vortex. The results also show the distribution of vorticity along the wake sheet and within the trailing vortex.
    Keywords: AERODYNAMICS
    Type: NASA-TP-3577 , A-950078 , NAS 1.60:3577 , ATCOM-TR-95-A-006
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  • 69
    Publication Date: 2019-06-28
    Description: This report summarizes the research performed by North Carolina State University and NASA Ames Research Center under Cooperative Agreement NCA2-719, 'Numerical Simulation of Supersonic and Hypersonic Inlet Flow Fields". Four distinct rotated upwind schemes were developed and investigated to determine accuracy and practicality. The scheme found to have the best combination of attributes, including reduction to grid alignment with no rotation, was the cell centered non-orthogonal (CCNO) scheme. In 2D, the CCNO scheme improved rotation when flux interpolation was extended to second order. In 3D, improvements were less dramatic in all cases, with second order flux interpolation showing the least improvement over grid aligned upwinding. The reduction in improvement is attributed to uncertainty in determining optimum rotation angle and difficulty in performing accurate and efficient interpolation of the angle in 3D. The CCNO rotational technique will prove very useful for increasing accuracy when second order interpolation is not appropriate and will materially improve inlet flow solutions.
    Keywords: AERODYNAMICS
    Type: NASA-CR-199428 , NAS 1.26:199428
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  • 70
    Publication Date: 2019-01-25
    Description: Solar Concentrator Array with Refractive Linear Element Technology (SCARLET) is one of the first practical photovoltaic concentrator array technologies that offers a number of benefits for space applications (i.e. high array efficiency, protection from space radiation effects, a relatively light weight system, minimized plasma interactions, etc.) The line-focus concentrator concept, however, also offers two very important advantages: (1) low-cost mass production potential of the lens material; and (2) relaxation of precise array tracking requirements to only a single axis. These benefits offer unique capabilities to both commercial and government spacecraft users, specifically those interested in high radiation missions, such as MEO orbits, and electric-powered propulsion LEO-to-GEO orbit raising applications. SCARLET is an aggressive hardware development and flight validation program sponsored by the Ballistic Missile Defense Organization (BMDO) and NASA Lewis Research Center. Its intent is to bring technology to the level of performance and validation necessary for use by various government and commercial programs. The first phase of the SCARLET program culminated with the design, development and fabrication of a small concentrator array for flight on the METEOR satellite. This hardware will be the first in-space demonstration of concentrator technology at the 'array level' and will provide valuable in-orbit performance measurements. The METEOR satellite is currently planned for a September/October 1995 launch. The next phase of the program is the development of large array for use by one of the NASA New Millenium Program missions. This hardware will incorporate a number of the significant improvements over the basic METEOR design. This presentation will address the basic SCARLET technology, examine its benefits to users, and describe the expected improvements for future missions.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: Proceedings of the 14th Space Photovoltaic Research and Technology Conference (SPRAT 14); p 4
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  • 71
    Publication Date: 2019-01-25
    Description: Improvements to GaAs solar array performance, from the use on solar cell coverslides of several reflecting coatings that reject unusable portions of the solar spectrum, are quantified. Blue-red-rejection (BRR) coverslides provide both infrared reflection (IRR) and ultraviolet rejection (UVR). BRR coverslides were compared to conventional antireflection (AR) and ultraviolet (UV) coated coverslides. A 2% improvement in peak-power output, relative to that from Ar-coated coverslides, is seen for cells utilizing BRR coverslides with the widest bandpass. Coverslide BRR-filter bandpass width and covered-solar-cell short-circuit current is a function of incident light angle and the observed narrower-bandpass filters are more sensitive to change in angle from the normal than are wide-bandpass filters. The first long-term (3000 hours) UV testing of unirradiated and 1 MeV electron-irradiated GaAs solar cells, with multilayer-coated coverslides to reduce solar array operating temperature, has indicated that all multilayer coatings on coverslides and solar cells will experience degradation from the space environment (UV and/or electrons). Five types of coverslide coatings, designed for GaAs solar cells, were tested as part of a NASA-sponsored space-flight qualification for BRR, multi-layer-coated, coverslides. The reponse to the different radiations varied with the coatings. The extent of degradation and its consequences on the solar cell electrical characteristics depend upon the coatings and the radiation. In some cases, an improved optical coupling was observed during long-term UV exposure to the optical stack. The benefits of multi-layered solar cell optics may depend upon both the duration and the radiation environment of a mission.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Lewis Research Center, Proceedings of the 14th Space Photovoltaic Research and Technology Conference (SPRAT 14); p 37
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  • 72
    Publication Date: 2019-01-25
    Description: The first commercial communications satellite with gallium-arsenide on germanium (GaAs/Ge) solar arrays is scheduled for launch in December 1995. The spacecraft, named MEASAT, was built by hughes Space and Telecommunications company for Binariang Satellite Systems of Malaysia. The solar cell assemblies consisted of large area GaAs/Ge cells supplied by Spectrolab Inc. with infrared reflecting (IRR) coverglass supplied by Pilkington Space Technology. A comprehensive characterization program was performed on the GaAs/Ge solar cell assemblies used on the MEASAT array. This program served two functions; first to establish the database needed to accurately predict on-orbit performance under a variety of conditions; and second, to demonstrate the ability of the solar cell assemblies to withstand all mission environments while still providing the required power at end-of-life. characterization testing included measurement of electrical performance parameters as a function of radiation exposure, temperature, and angle of incident light; reverse bias stability; optical and thermal properties; mechanical strength tests, panel fabrication, humidity and thermal cycling environmental tests. The results provided a complete database enabling the design of the MEASAT solar array, and demonstrated that the GaAs/Ge cells meet the spacecraft requirements at end-of-life.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Lewis Research Center, Proceedings of the 14th Space Photovoltaic Research and Technology Conference (SPRAT 14); p 34
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  • 73
    Publication Date: 2019-01-25
    Description: The Photovoltaic Array Space Power Plus Diagnostics (PASP Plus) experiment was developed by the Air Force's Phillips Laboratory with support from NASA's Lewis Research Center. It was launched on the Advanced Photovoltaic and Electronics EXperiments (APEX) satellite on August 3, 1994 into a 70 degree inclination, 363 km by 2550 km elliptical orbit. This orbit allows the investigation of space plasma effects on high-voltage operation (leakage current at positive voltages and arcing at negative voltages) in the perigee region. PASP Plus is testing twelve solar arrays. There are four planar Si arrays: an old standard type (used as a reference), the large-cell Space Station Freedom (SSF) array, a thin 'APSA' array, and an amorphous Si array. Next are three GaAs on Ge planar arrays and three new material planar arrays, including InP and two multijunction types. Finally, there are two concentrator arrays: a reflective-focusing Mini-Cassegrainian and a Fresnel-lens focusing Mini-Dome. PASP Plus's diagnostic sensors include: Langmuir probe to measure plasma density, an electrostatic analyzer (ESA) to measure the 30 eV to 30 KeV electron/ion spectra and determine vehicle negative potential during positive biasing, and a transient pulse monitor (TPM) to characterize the arcs that occur during the negative biasing. Through positive biasing of its test arrays, PASP Plus investigated the snapover phenomenon, which took place over the range of +100 to +300 V. It was found that array configurations where the interconnects are shielded from the space plasma (i.e., the concentrators or arrays with 'wrap-through' connectors) have lower leakage current. The concentrators exhibited negligible leakage current over the whole range up to +500 V. In the case of two similar GaAs on Ge arrays, the one with 'wrap-through' connectors had lower leakage current than the one with conventional interconnects. Through negative biasing, PASP Plus investigated the arcing rates of its test arrays. The standard Si array, with its old construction (exposed rough-surface interconnects), arced significantly over a wide voltage and plasma-density range. The other arrays arced at very low rates, mostly at voltages greater than -350 V and plasma densities near or greater than 10(exp 5)/cm(exp -3). AS expected according to theory, arcing was more prevalent when array temperatures were cold (based on biasing in eclipse).
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Lewis Research Center, Proceedings of the 14th Space Photovoltaic Research and Technology Conference (SPRAT 14); p 41
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  • 74
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    In:  Other Sources
    Publication Date: 2019-01-25
    Description: This paper describes solar cell panel designs that utilize new hgih efficiency solar cells along with lightweight rigid panel technology. The resulting designs push the W/kg and W/sq m parameters to new high levels. These new designs are well suited to meet the demand for higher performance small satellites. This paper reports on progress made on two SBIR Phase 1 contracts. One panel design involved the use of large area (5.5 cm x 6.5 cm) GaAs/Ge solar cells of 19% efficiency combined with a lightweight rigid graphite fiber epoxy isogrid substrate configuration. A coupon (38 cm x 38 cm) was fabricated and tested which demonstrated an array specific power level of 60 W/kg with a potential of reaching 80 W/kg. The second panel design involved the use of newly developed high efficiency (22%) dual junction GaInP2/GaAs/Ge solar cells combined with an advanced lightweight rigid substrate using aluminum honeycomb core with high strength graphite fiber mesh facesheets. A coupon (38 cm x 38 cm) was fabricated and tested which demonstrated an array specific power of 105 W/kg and 230 W/sq m. This paper will address the construction details of the panels and an a analysis of the component weights. A strawman array design suitable for a typical small-sat mission is described for each of the two panel design technologies being studied. Benefits in respect to weight reduction, area reduction, and system cost reduction are analyzed and compared to conventional arrays.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Lewis Research Center, Proceedings of the 14th Space Photovoltaic Research and Technology Conference (SPRAT 14); p 36
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  • 75
    Publication Date: 2019-01-25
    Description: Solar cells at potentials positive with respect to a surrounding plasma collect electrons. Current is collected by the exposed high voltage surfaces: the interconnects and the sides of the solar cells. This current is a drain on the array power that can be significant for high-power arrays. In addition, this current influences the current balance that determines the floating potential of the spacecraft. One of the objectives of the Air Force (PL/GPS) PASP Plus (Photovoltaic Array Space Power Plus Diagnostics) experiment is an improved understanding fo parasitic current collection. We have done computer modeling of parasitic current collection and have examined current collection flight data from the first year of operations. Prior to the flight we did computer modeling to improve our understanding of the physical processes that control parasitic current collection. At high potentials, the current rapidly rises due to a phenomenon called snapover. Under snapover conditions, the equilibrium potential distribution across the dielectric surface is such that part of the area is at potentials greater than the first crossover of the secondary yield curve. Therefore, each incident electron generates more than one secondary electron. The net effect is that the high potential area and the collecting area increase. We did two-dimensional calculations for the various geometries to be flown. The calculations span the space of anticipated plasma conditions, applied potential, and material parameters. We used the calculations and early flight data to develop an analytic formula for the dependence of the current on the primary problem variables. The analytic formula was incorporated into the EPSAT computer code. EPSAT allows us to easily extend the results to other conditions. PASP Plus is the principal experiment integrated onto the Advanced Photovoltaic and Electronics Experiments (APEX) satellite bus. The experiment is testing twelve different solar array designs. Parasitic current collection is being measured for eight of the designs under various operational and environment conditions. We examined the current collected as a function of the various parameters for the six non-concentrator designs. The results are similar to those obtained in previous experiments and predicted by the calculations. We are using the flight data to validate the analytic formula developed. The formula can be used to quantify the parasitic current collected. Anticipating the parasitic current value allows the spacecraft designer to include this interaction when developing the design.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Lewis Research Center, Proceedings of the 14th Space Photovoltaic Research and Technology Conference (SPRAT 14); p 40
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  • 76
    Publication Date: 2019-01-25
    Description: A radioisotope thermophotovoltaic generator space power system (RTPV) is lightweight, low-cost alternative to the present radioisotope thermoelectric generator system (RTG). The fabrication of such an RTPV generator has recently become feasible as the result of the invention of the GaSb infrared sensitive photovoltaic cell. Herein, we present the results of a parametric study of emitters and optical filters in conjuction with existing data on gallium antimonide cells. We compare a polished tungsten emitter with an Erbia selective emitter for use in combination with a simple dielectric filter and a gallium antimonide cell array. We find that the polished tungsten emitter is by itself a very selective emitter with low emissivity beyond 4 microns. Given a gallium antimonide cell and a tungsten emitter, a simple dielectric filter can be designed to transmit radiant energy below 1.7 microns and to reflect radiant energy between 1.7 and 4 microns back to the emitter. Because of the low long wavelength emissivity associated with the polished tungsten emitter, this simple dielectric filter then yields very respectable system performance. Also as a result of the longer wavelength fall-off in the tungsten emissivity curve, the radiation energy peak for a polished tungsten emitter operating at 1300 K shifts to shorter wavelengths relative to the blackbody spectrum so that the radiated energy peak falls right at the gallium antimonide cell bandedge. The result is that the response of the gallium antimonide cell is well matched to a polished tungsten emitter. We propose, therefore, to fabricate an operating prototype of a near term radioisotope thermophotovoltaic generator design consisting of a polished tungsten emitter, standard gallium antimonide cells, and a near-term dielectric filter. The Jet Propulsion Laboratory will design and build the thermal cavity, and JX Crystals will fabricate the gallium antimonide cells, dielectric filters, and resultant receiver panels. With 250 Watts of heat input, we expect this prototype to produce over 300 Watts of electrical energy output for a system energy conversion efficiency of over 12%. This low risk, near term design provides advances relative to present radioisotope thermophotovoltaic generators and has the additional advantage of allowing component and system development and testing to begin immediately. Improved cells and filters can easily be incorporated in this baseline system if they should become available in the future.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Lewis Research Center, Proceedings of the 14th Space Photovoltaic Research and Technology Conference (SPRAT 14); p 30
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  • 77
    Publication Date: 2019-01-25
    Description: The Naval Research Laboratory has been involved in developing InP solar cell technology since 1988. The purpose of these programs was to produce advanced cells for use in very high radiation environments, either as a result of operating satellites in the Van Allen belts or for very long duration missions in other orbits. Richard Statler was technical representative on the first program, with Spire Corporation as the contractor, which eventually produced several hundred, high efficiency 2 x 2 sq cm single crystal InP cells. The shallow homojunction technology which was developed in this program enabled cells to be made with AMO, one sun efficiencies greater than 19%. Many of these cells have been flown on space experiments, including PASP Plus, which have confirmed the high radiation resistance of InP cells. NRL has also published widely on the radiation response of these cells and also on radiation-induced defect levels detected by DLTS, especially the work of Rob Walters and Scott Messenger. In 1990 NRL began another Navy-sponsored program with Tim Coutts and Mark Wanlass at the National Renewable Energy Laboratory (NREL), to develop a one sun, two terminal space version of the InP-InGaAs tandem junction cell being investigated at NREL for terrestrial applications. These cells were grown on InP substrates. Several cells with AM0, one sun efficiencies greater than 22% were produced. Two 2 x 2 sq cm cells were incorporated on the STRV lA/B solar cell experiment. These were the only two junction, tandem cells on the STRV experiment. The high cost and relative brittleness of InP wafers meant that if InP cell technology were to become a viable space power source, the superior radiation resistance of InP would have to be combined with a cheaper and more robust substrate. The main technical challenge was to overcome the effect of the dislocations produced by the lattice mismatch at the interface of the two materials. Over the last few years, NRL and Steve Wojtczuk at Spire have been developing a single junction InP on Si cell, in an ONR-sponsored SBIR program. Both cell polarities were investigated and the best efficiencies to date (approximately 13% on a 2 x 4 sq cm cell) were achieved with n/p cells. Earlier this year NRL began a program with ASEC to develop a two terminal InP-InGaAs tandem cell on a Ge substrate. RTI and NREL are subcontractors on this program. The results of an ONR-sponsored study of the potential market for InP/Si cells will be discussed. Also the technical status of both the InP/Si and the InP-InGaAs/Ge programs will be given. The technical challenges still remaining will be briefly described.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Lewis Research Center, Proceedings of the 14th Space Photovoltaic Research and Technology Conference (SPRAT 14); p 7
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  • 78
    Publication Date: 2019-01-25
    Description: In the past 25 years, the majority of interplanetary spacecraft have been powered by nuclear sources. However, as the emphasis on smaller, low cost missions gains momentum, the majority of missions now being planned will use photovoltaic solar arrays. This will present challenges to the solar array builders, inasmuch as planetary requirements usually differ from earth orbital requirements. In addition, these requirements often differ greatly, depending on the specific mission; for example, inner planets vs. outer planets, orbiters vs. flybys, spacecraft vs. landers, and so on. Also, the likelihood of electric propulsion missions will influence the requirements placed on solar array developers. The paper will discuss representative requirements for a range of planetary missions now in the planning stages. Insofar as inner planets are concerned, a Mercury orbiter is being studied with many special requirements. Solar arrays would be exposed to high temperatures and a potentially high radiation environment, and will need to be increasingly pointed off sun as the vehicle approaches Mercury. Identification and development of cell materials and arrays at high incidence angles will be critical to the design. Missions to the outer solar system that have been studied include a Galilean orbiter and a flight to the Kuiper belt. While onboard power requirements would be small (as low as 10 watts), the solar intensity will require relatively large array areas. As a result, such missions will demand extremely compact packaging and low mass structures to conform to launch vehicle constraints. In turn, the large are, low mass designs will impact allowable spacecraft loads. Inflatable array structures, with and without concentration, and multiband gap cells will be considered if available. In general, the highest efficiency cell technologies operable under low intensity, low temperature conditions are needed. Solar arrays will power missions requiring as little as approximately 100 watts, up to several kilowatts (at Earth) in the case of solar electric propulsion missions. Thus, mass and stowage volume minimization will be required over a range of array sizes. Concentrator designs, inflatable structures, and the combination of solar arrays with the telecommunications system have been proposed. Performance, launch vehicle constraints, an cost will be the principal parameters in the design trade space. Other special applications will also be discussed, including requirements relating to planetary landers and probes. In those cases, issues relating to shock loads on landing, operability in (possibly dusty) atmospheres, and extreme temperature cycles must be considered, in addition to performance, stowed volume, and costs.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Lewis Research Center, Proceedings of the 14th Space Photovoltaic Research and Technology Conference (SPRAT 14); p 5
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  • 79
    Publication Date: 2019-06-28
    Description: Aeroelastic stability analyses have been performed for the MOD-5A blade/aileron system. Various configurations having different aileron torsional stiffness, mass unbalance, and control system damping have been investigated. The analysis was conducted using a code recently developed by the General Electric Company - AILSTAB. The code extracts eigenvalues for a three degree of freedom system, consisting of: (1) a blade flapwise mode; (2) a blade torsional mode; and (3) an aileron torsional mode. Mode shapes are supplied as input and the aileron can be specified over an arbitrary length of the blade span. Quasi-steady aerodynamic strip theory is used to compute aerodynamic derivatives of the wing-aileron combination as a function of spanwise position. Equations of motion are summarized herein. The program provides rotating blade stability boundaries for torsional divergence, classical flutter (bending/torsion) and wing/aileron flutter. It has been checked out against fixed-wing results published by Theodorsen and Garrick. The MOD-5A system is stable with respect to divergence and classical flutter for all practical rotor speeds. Aileron torsional stiffness must exceed a minimum critical value to prevent aileron flutter. The nominal control system stiffness greatly exceeds this minimum during normal operation. The basic system, however, is unstable for the case of a free (or floating) aileron. The instability can be removed either by the addition of torsional damping or mass-balancing the ailerons. The MOD-5A design was performed by the General Electric Company, Advanced Energy Program Department under Contract DEN3-153 with NASA Lewis Research Center and sponsored by the Department of Energy.
    Keywords: AERODYNAMICS
    Type: DASCON Engineering, Collected Papers on Wind Turbine Technology; p 99-114
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  • 80
    Publication Date: 2019-06-28
    Description: A method has been developed to accurately compute the viscous flow in three-dimensional (3-D) enclosures. This method is the 3-D extension of a two-dimensional (2-D) method developed for the calculation of flow over airfoils. The 2-D method has been tested extensively and has been shown to accurately reproduce experimental results. As in the 2-D method, the 3-D method provides for the non-iterative solution of the incompressible Navier-Stokes equations by means of a fully coupled implicit technique. The solution is calculated on a body fitted computational mesh incorporating a staggered grid methodology. In the staggered grid method, the three components of vorticity are defined at the centers of the computational cell sides, while the velocity components are defined as normal vectors at the centers of the computational cell faces. The staggered grid orientation provides for the accurate definition of the vorticity components at the vorticity locations, the divergence of vorticity at the mesh cell nodes and the conservation of mass at the mesh cell centers. The solution is obtained by utilizing a fractional step solution technique in the three coordinate directions. The boundary conditions for the vorticity and velocity are calculated implicitly as part of the solution. The method provides for the non-iterative solution of the flow field and satisfies the conservation of mass and divergence of vorticity to machine zero at each time step. To test the method, the calculation of simple driven cavity flows have been computed. The driven cavity flow is defined as the flow in an enclosure driven by a moving upper plate at the top of the enclosure. To demonstrate the ability of the method to predict the flow in arbitrary cavities, results will he shown for both cubic and curved cavities.
    Keywords: AERODYNAMICS
    Type: NASA-TM-110352 , A-950063 , NAS 1.15:110352
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  • 81
    Publication Date: 2019-06-28
    Description: An effort to understand and control the unsteady separated flow associated with the dynamic stall of airfoils was funded for three years through the NASA cooperative agreement program. As part of this effort a substantial data base was compiled detailing the effects various parameters have on the development of the dynamic stall flow field. Parameters studied include Mach number, pitch rate, and pitch history, as well as Reynolds number (through two different model chord lengths) and the condition of the boundary layer at the leading edge of the airfoil (through application of surface roughness). It was found for free stream Mach numbers as low as 0.4 that a region of supersonic flow forms on the leading edge of the suction surface of the airfoil at moderate angles of attack. The shocks which form in this supersonic region induce boundary-layer separation and advance the dynamic stall process. Under such conditions a supercritical airfoil profile is called for to produce a flow field having a weaker leading-edge pressure gradient and no leading-edge shocks. An airfoil having an adaptive-geometry, or dynamically deformable leading edge (DDLE), is under development as a unique active flow-control device. The DDLE, formed of carbon-fiber composite and fiberglass, can be flexed between a NACA 0012 profile and a supercritical profile in a controllable fashion while the airfoil is executing an angle-of-attack pitch-up maneuver. The dynamic stall data were recorded using point diffraction interferometry (PDI), a noninvasive measurement technique. A new high-speed cinematography system was developed for recording interferometric images. The system is capable of phase-locking with the pitching airfoil motion for real-time documentation of the development of the dynamic stall flow field. Computer-aided image analysis algorithms were developed for fast and accurate reduction of the images, improving interpretation of the results.
    Keywords: AERODYNAMICS
    Type: NASA-CR-198972 , NAS 1.26:198972 , MCAT-95-09
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  • 82
    Publication Date: 2019-06-28
    Description: A numerical scheme utilizing a chimera zonal grid approach for solving the full potential equation in two spatial dimensions is described. Within each grid zone a fully-implicit approximate factorization scheme is used to advance the solution one interaction. This is followed by the explicit advance of all common zonal grid boundaries using a bilinear interpolation of the velocity potential. The presentation is highlighted with numerical results simulating the flow about a two-dimensional, nonlifting, circular cylinder. For this problem, the flow domain is divided into two parts: an inner portion covered by a polar grid and an outer portion covered by a Cartesian grid. Both incompressible and compressible (transonic) flow solutions are included. Comparisons made with an analytic solution as well as single grid results indicate that the chimera zonal grid approach is a viable technique for solving the full potential equation.
    Keywords: AERODYNAMICS
    Type: NASA-TM-110360 , A-950082 , NAS 1.15:110360
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  • 83
    Publication Date: 2019-06-28
    Description: Distributions of static pressure coefficient over the afterbody and axisymmetric nozzles of a generic, twin-tail twin-engine fighter were obtained in the Langley 16-Foot Transonic Tunnel. The longitudinal positions of the vertical and horizontal tails were varied for a total of six aft-end configurations. Static pressure coefficients were obtained at Mach numbers between 0.6 and 1.2, angles of attack between 0 deg and 8 deg, and nozzle pressure ratios ranging from jet-off to 8. The results of this investigation indicate that the influence of the vertical and horizontal tails extends beyond the vicinity of the tail-afterbody juncture. The pressure distribution affecting the aft-end drag is influenced more by the position of the vertical tails than by the position of the horizontal tails. Transonic tail-interference effects are seen at lower free-stream Mach numbers at positive angles of attack than at an angle of attack of 0 deg.
    Keywords: AERODYNAMICS
    Type: NASA-TP-3509 , L-17438 , NAS 1.60:3509
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  • 84
    Publication Date: 2019-06-28
    Description: The National Aeronautics and Space Administration and the Defense Research Agency (United Kingdom) have ongoing experimental research programs in rotary-flow aerodynamics. A cooperative effort between the two agencies is currently underway to collect an extensive database for the development of high angle of attack computational methods to predict the effects of Reynolds number on the forebody flowfield at dynamic conditions, as well as to study the use of low Reynolds number data for the evaluation of high Reynolds number characteristics. Rotary balance experiments, including force and moment and surface pressure measurements, were conducted on circular and rectangular aftbodies with hemispherical and ogive noses at the Bedford and Farnborough wind tunnel facilities in the United Kingdom. The bodies were tested at 60 and 90 deg angle of attack for a wide range of Reynolds numbers in order to observe the effects of laminar, transitional, and turbulent flow separation on the forebody characteristics when rolling about the velocity vector.
    Keywords: AERODYNAMICS
    Type: NASA-CR-195033 , REPT-94-4 , NAS 1.26:195033
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  • 85
    Publication Date: 2019-06-28
    Description: A wind-tunnel investigation of the effectiveness of an aerodynamic yaw controller mounted on the lower surface of a shuttle orbiter model body flap was conducted in the Langley 31-Inch Mach 10 Tunnel. The controller consisted of a 60 deg delta fin mounted perpendicular to the body flap lower surface and yawed 30 deg to the free stream direction. The control was tested at angles of attack from 20 deg to 40 deg at zero sideslip for a Reynolds number based on wing mean aerodynamic chord of 0.66 x 10(exp 6). The aerodynamic and control effectiveness characteristics are presented along with an analysis of the effectiveness of the controller in making a bank maneuver for Mach 18 flight conditions. The controller was effective in yaw and produced a favorable rolling moment. The analysis showed that the controller was as effective as the reaction control system in making the bank maneuver. These results warrant further studies of the aerodynamic/aerothermodynamic characteristics of the control concept for application to future transportation vehicles.
    Keywords: AERODYNAMICS
    Type: NASA-TM-109179 , NAS 1.15:109179
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  • 86
    Publication Date: 2019-06-28
    Description: The approach to carrying out multi-discipline aerospace design studies in the future, especially in massively parallel computing environments, comprises of choosing (1) suitable solvers to compute solutions to equations characterizing a discipline, and (2) efficient optimization methods. In addition, for aerodynamic optimization problems, (3) smart methodologies must be selected to modify the surface shape. In this research effort, a 'direct' optimization method is implemented on the Cray C-90 to improve aerodynamic design. It is coupled with an existing implicit Navier-Stokes solver, OVERFLOW, to compute flow solutions. The optimization method is chosen such that it can accomodate multi-discipline optimization in future computations. In the work , however, only single discipline aerodynamic optimization will be included.
    Keywords: AERODYNAMICS
    Type: NASA-CR-198045 , NAS 1.26:198045 , OMI-02-93
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  • 87
    Publication Date: 2019-06-28
    Description: Modeling enhancements made to a radial-inflow turbine conceptual design code are documented in this report. A stator-endwall clearance-flow model was added for use with pivoting vanes. The rotor calculations were modified to account for swept blades and splitter blades. Stator and rotor trailing-edge losses and a vaneless-space loss were added to the loss model. Changes were made to the disk-friction and rotor-clearance loss calculations. The loss model was then calibrated based on experimental turbine performance. A complete description of code input and output along with sample cases are included in the report.
    Keywords: AERODYNAMICS
    Type: NASA-CR-195454 , E-9538 , NAS 1.26:195454
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  • 88
    Publication Date: 2019-06-28
    Description: Internal fluid flows are subject not only to self-sustained oscillations of the purely hydrodynamic type but also to the coupling of the instability with the acoustic mode of the surrounding cavity. This situation is common to turbomachinery, since flow instabilities are confined within a flow path where the acoustic wavelength is typically smaller than the dimensions of the cavity and flow speeds are low enough to allow resonances. When acoustic coupling occurs, the fluctuations can become so severe in amplitude that it may induce structural failure of engine components. The potential for catastrophic failure makes identifying flow-induced noise and vibration sources a priority. In view of the complexity of these types of flows, this report was written with the purpose of presenting many of the methods used to compute frequencies for self-sustained oscillations. The report also presents the engineering formulae needed to calculate the acoustic resonant modes for ducts and cavities. Although the report is not a replacement for more complex numerical or experimental modeling techniques, it is intended to be used on general types of flow configurations that are known to produce self-sustained oscillations. This report provides a complete collection of these models under one cover.
    Keywords: AERODYNAMICS
    Type: NASA-CR-4671 , M-778 , NAS 1.26:4671
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  • 89
    Publication Date: 2019-06-28
    Description: This study was conducted to experimentally characterize the flow field created by the interaction of a single-expansion ramp-nozzle (SERN) flow with a hypersonic external stream. Data were obtained from a generic nozzle/afterbody model in the 3.5 Foot Hypersonic Wind Tunnel at the NASA Ames Research Center, in a cooperative experimental program involving Ames and McDonnell Douglas Aerospace. The model design and test planning were performed in close cooperation with members of the Ames computational fluid dynamics (CFD) team for the National Aerospace Plane (NASP) program. This paper presents experimental results consisting of oil-flow and shadow graph flow-visualization photographs, afterbody surface-pressure distributions, rake boundary-layer measurements, Preston-tube skin-friction measurements, and flow field surveys with five-hole and thermocouple probes. The probe data consist of impact pressure, flow direction, and total temperature profiles in the interaction flow field.
    Keywords: AERODYNAMICS
    Type: NASA-TM-4638 , A-94119 , NAS 1.15:4638
    Format: application/pdf
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  • 90
    Publication Date: 2019-06-28
    Description: A methodology is described for computing viscous flows of air and sulfur hexafluoride (SF6). The basis is an existing flow solver that calculates turbulent flows in two dimensions on unstructured triangular meshes. The solver has been modified to incorporate the thermodynamic model for SF6 and used to calculate the viscous flow over two multielement airfoils that have been tested in a wind tunnel with air as the test medium. Flows of both air and SF6 at a free-stream Mach number of 0.2 and a Reynolds number of 9 x 10(exp 6) are computed for a range of angles of attack corresponding to the wind-tunnel test. The computations are used to investigate the suitability of SF6 as a test medium in wind tunnels and are a follow-on to previous computations for single-element airfoils. Surface-pressure, lift, and drag coefficients are compared with experimental data. The effects of heavy gas on the details of the flow are investigated based on computed boundary-layer and skin-friction data. In general, the predictions in SF6 vary little from those in air. Within the limitations of the computational method, the results presented are sufficiently encouraging to warrant further experiments.
    Keywords: AERODYNAMICS
    Type: NASA-TP-3496 , L-17401 , NAS 1.60:3496
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  • 91
    Publication Date: 2019-06-28
    Description: It is well known in the aerodynamic field that pressure distribution measurement over the surface of an aircraft model is a problem in experimental aerodynamics. For one thing, a continuous pressure map can not be obtained with the current experimental methods since they are discrete. Therefore, interpolation or CFD methods must be used for a more complete picture of the phenomenon under study. For this study, a new technique was investigated which would provide a continuous pressure distribution over the surface under consideration. The new method is pressure sensitive paint. When pressure sensitive paint is applied to an aerodynamic surface and placed in an operating wind-tunnel under appropriate lighting, the molecules luminesce as a function of the local pressure of oxygen over the surface of interest during aerodynamic flow. The resulting image will be brightest in the areas of low pressure (low oxygen concentration), and less intense in the areas of high pressure (where oxygen is most abundant on the surface). The objective of this investigation was to use pressure sensitive paint samples from McDonnell Douglas (MDD) for calibration purpose in order to assess the response of the paint under appropriate lighting and to use the samples over a flat plate/conical fin mounted at 75 degrees from the center of the plate in order to study the shock/boundary layer interaction at Mach 6 in the Von Karman wind-tunnel. From the result obtained it was concluded that temperature significantly affects the response of the paint and should be given the uppermost attention in the case of hypersonic flows. Also, it was found that past a certain temperature threshold, the paint intensity degradation became irreversible. The comparison between the pressure tap measurement and the pressure sensitive paint showed the right trend. However, there exists a shift when it comes to the actual value. Therefore, further investigation is under way to find the cause of the shift.
    Keywords: AERODYNAMICS
    Type: NASA-TM-106824 , E-9373 , NAS 1.15:106824
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  • 92
    Publication Date: 2019-06-28
    Description: The objective of this study was to examine the overall feasibility of deploying electromechanical flywheel systems in space used for excess energy storage. Results of previous Rocketdyne studies have shown that the flywheel concept has a number of advantages over the NiH2 battery, including higher specific energy, longer life and high roundtrip efficiency. Based on this prior work, this current study was broken into four subtasks. The first subtask investigated the feasibility of replacing the NiH2 battery orbital replacement unit (ORU) on the international space station (ISSA) with a flywheel ORU. In addition, a conceptual design of a generic flywheel demonstrator experiment implemented on the ISSA was completed. An assessment of the life cycle cost benefits of replacing the station battery energy storage ORU's with flywheel ORU's was performed. A fourth task generated a top-level development plan for critical flywheel technologies, the flywheel demonstrator experiments and its evolution into the production unit flywheel replacement ORU.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA-CR-195422 , E-9367 , NAS 1.26:195422
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  • 93
    Publication Date: 2019-06-28
    Description: Longitudinal characteristics and wing-section pressure distributions are compared for the EA-6B airplane with and without airfoil modifications. The airfoil modifications were designed to increase low-speed maximum lift for maneuvering, while having a minimal effect on transonic performance. Section contour changes were confined to the leading-edge slat and trailing-edge flap regions of the wing. Experimental data are analyzed from tests in the Langley 16-Foot Transonic Tunnel on the baseline and two modified wing-fuselage configurations with the slats and flaps in their retracted positions. Wing modification effects on subsonic and transonic performance are seen in wing-section pressure distributions of the various configurations at similar lift coefficients. The modified-wing configurations produced maximum lift coefficients which exceeded those of the baseline configuration at low-speed Mach numbers (0.300 and 0.400). This benefit was related to the behavior of the wing upper surface leading-edge suction peak and the behavior of the trailing-edge pressure. At transonic Mach numbers (0.725 to 0.900), the wing modifications produced a somewhat stronger nose-down pitching moment, a slightly higher drag at low-lift levels, and a lower drag at higher lift levels.
    Keywords: AERODYNAMICS
    Type: NASA-TP-3516 , L-17360 , NAS 1.60:3516
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  • 94
    Publication Date: 2019-06-28
    Description: This report describes the aerodynamics model used in a simulation model of an advanced short takeoff and vertical landing (ASTOVL) lift-fan fighter aircraft. The simulation model was developed for use in piloted evaluations of transition and hover flight regimes, so that only low speed (M approximately 0.2) aerodynamics are included in the mathematical model. The aerodynamic model includes the power-off aerodynamic forces and moments and the propulsion system induced aerodynamic effects, including ground effects. The power-off aerodynamics data were generated using the U.S. Air Force Stability and Control Digital DATCOM program and a NASA Ames in-house graphics program called VORVIEW which allows the user to easily analyze arbitrary conceptual aircraft configurations using the VORLAX program. The jet-induced data were generated using the prediction methods of R. E. Kuhn et al., as referenced in this report.
    Keywords: AERODYNAMICS
    Type: NASA-TM-110347 , A-950051 , NAS 1.15:110347
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  • 95
    Publication Date: 2019-06-28
    Description: A flow visualization study of several configurations of a jet-powered vertical takeoff and landing (VTOL) aircraft model during hover in ground effect was conducted. A surface oil flow technique was used to observe the flow patterns on the lower surfaces of the model. There were significant configuration effects. Wing height with respect to fuselage, the presence of an engine inlet duct beside the fuselage, and nozzle pressure ratio are seen to have strong effects on the surface flow angles on the lower surface of the wing. This test was part of a program to improve the methods for predicting the hot gas ingestion (HGI) for jet-powered vertical/short takeoff and landing (V/STOL) aircraft. The tests were performed at the Jet Calibration and Hover Test (JCAHT) Facility at Ames Research Center.
    Keywords: AERODYNAMICS
    Type: NASA-TM-108860 , A-95025 , NAS 1.15:108860
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  • 96
    Publication Date: 2019-06-28
    Description: Comprehensive experimental and analytical studies have been conducted to assess the potential aerodynamic benefits from spanwise blowing at the tip of a moderate-aspect-ratio swept wing. Previous studies on low-aspect-ratio wings indicated that blowing from the wingtip can diffuse the tip vortex and displace it outward. The diffused and displaced vortex will induce a smaller downwash at the wing, and consequently the wing will have increased lift and decreased induced drag at a given angle of attack. Results from the present investigation indicated that blowing from jets with a short chord had little effect on lift or drag, but blowing from jets with a longer chord increased lift near the tip and reduced drag at low Mach numbers. A Navier-Stokes solver with modified boundary conditions at the tip was used to extrapolate the results to a Mach number of 0.72. Calculations indicated that lift and drag increase with increasing jet momentum coefficient. Because the momentum of the jet is typically greater than the reduction in the wing drag and the increase in the wing lift due to spanwise blowing is small, spanwise blowing at the wingtip does not appear to be a practical means of improving the aerodynamic efficiency of moderate-aspectratio swept wings at high subsonic Mach numbers.
    Keywords: AERODYNAMICS
    Type: NASA-TP-3515 , L-17368 , NAS 1.60:3515
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  • 97
    Publication Date: 2019-06-28
    Description: This report summarizes accomplishments and progress for the period ending April 1995. Much of the work during this period has concentrated on preparation for an analysis of data produced by an extensive wind tunnel test. Time has also been spent further developing an empirical theory to account for the effects of blade-vortex interaction upon the circulation distribution of the vortex and on preliminary measurements aimed at controlling the vortex core size.
    Keywords: AERODYNAMICS
    Type: NASA-CR-198590 , NAS 1.26:198590
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  • 98
    Publication Date: 2019-06-28
    Description: Blade-element/momentum performance prediction codes are routinely used for wind turbine design and analysis. A weakness of these codes is their inability to consistently predict peak power upon which the machine structural design and cost are strongly dependent. The purpose of this study was to compare post-stall airfoil characteristics synthesization theory to a systematically acquired wind tunnel data set in which the effects of aspect ratio, airfoil thickness, and Reynolds number were investigated. The results of this comparison identified discrepancies between current theory and the wind tunnel data which could not be resolved. Other factors not previously investigated may account for these discrepancies and have a significant effect on peak power prediction.
    Keywords: AERODYNAMICS
    Type: DASCON Engineering, Collected Papers on Wind Turbine Technology; p 35-39
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  • 99
    Publication Date: 2019-06-28
    Description: This paper summarizes results of several experiments flown on the Long Duration Exposure Facility (LDEF) to examine the effects of the space environment on materials and technologies to be used in solar arrays. The various LDEF experiments are compared to each other as well as to other solar cell flight data published in the literature. Data on environmental effects such as atomic oxygen, ultraviolet light, micrometeoroids and debris, and charged particles are discussed in detail. The results from the LDEF experiments allow us to draw several conclusions. Atomic oxygen erodes unprotected silver interconnects, unprotected Kapton, and polymer cell covers, but certain dielectric coatings can protect both silver and Kapton. Cells that had wrap-around silver contacts sometimes showed erosion at the edges, but more recently developed wrap-through cells are not expected to have these problems. Micrometeoroid and debris damage is limited to the area close to the impact, and microsheet covers provide the cells with some protection. Damage from charged particles was as predicted, and the cell covers provided adequate protection. In general, silicon cells with microsheet covers showed very little degradation, and solar modules showed less than 3 percent degradation, except when mechanically damaged. The solar cell choices for the Space Station solar array are supported by the data from LDEF.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Langley Research Center, LDEF: 69 Months in Space. Third Post-Retrieval Symposium, Part 3; p 1167-1177
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  • 100
    Publication Date: 2019-06-28
    Description: Test flights were conducted to evaluate the capability of Differential Global Positioning System (DGPS) to provide the accuracy and integrity required for International Civil Aviation Organization (ICAO) Category (CAT) 3 precision approach and landings. These test flights were part of a Federal Aviation Administration (FAA) program to evaluate the technical feasibility of using DGPS based technology for CAT 3 precision approach and landing applications. A United Airlines Boeing 737-300 (N304UA) was equipped with DGPS receiving equipment and additional computing capability provided by Stanford University. The test flights were conducted at NASA Ames Research Center's Crows Landing Flight Facility, Crows Landing, California. The flight test evaluation was based on completing 100 approaches and autolandings; 90 touch and go, and 10 terminating with a full stop. Two types of accuracy requirements were evaluated: 1) Total system error, based on the Required Navigation Performance (RNP), and 2) Navigation sensor error, based on ICAO requirements for the Microwave Landing System (MLS). All of the approaches and autolandings were evaluated against ground truth reference data provided by a laser tracker. Analysis of these approaches and autolandings shows that the Stanford University/United Airlines system met the requirements for a successful approach and autolanding 98 out of 100 approaches and autolandings, based on the total system error requirements as specified in the FAA CAT 3 Level 2 Flight Test Plan.
    Keywords: AERODYNAMICS
    Type: NASA-TM-110354 , A-950066 , NAS 1.15:110354
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