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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,765 records · Page 98

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NASA NTRS1973

Solar cell radiation handbook

A method is presented for predicting the degradation of a solar array in a space radiation environment. Solar cell technology which emphasizes the cell parameters that degrade in a radiation environment, is discussed along with the experimental techniques used in the evaluation of radiation effects. Other topics discussed include: theoretical aspects of radiation damage, methods for developing relative damage coefficients, nature of the space radiation environment, method of calculating equivalent fluence from electron and proton energy spectrums and relative damage coefficients, and comparison of flight data with estimated degradation.

Carter, J. R., Jr.↗

NASA NTRS1973

Study of regenerable CO2 sorbents for extravehicular activity

Studies have shown that frequent extravehicular activities planned for future space missions will require regenerable life support systems. The oxides of magnesium, zinc, and silver were tested for their ability to react with CO2 to form the corresponding carbonates, and subsequent thermal regeneration to the oxides. Catalysts and binders were investigated to enhance CO2 sorption rates and structural integrity. A silver oxide formulation was developed which rapidly absorbs 95% of its theoretical capacity and has shown no degradation through 28 regenerations.

Colombo, G. V.↗

NASA NTRS1974

Character of the pair interaction in solid and gaseous H2

Existing theoretical H2 pair potentials are investigated. We develop a spherically symmetric potential applicable to solid H2. It yields a ground-state energy of -98.7 K (experimental values range from -93.5 to -101 K). Pressure-volume data are also in excellent agreement with experiment between 0 and 25 kbar. Second virial coefficients using this potential are consistently too low. When an anisotropic pair potential is used, agreement becomes very good.

England, W.↗

NASA NTRS1975

Effect of symmetrical vortex shedding on the longitudinal aerodynamic characteristics of wing-body-tail combinations

An engineering prediction method for determining the longitudinal aerodynamic characteristics of wing-body-tail combinations is developed. The method includes the effects of nonlinear aerodynamics of components and the interference between components. Nonlinearities associated with symmetrical vortex shedding from the nose of the body are considered as well as the nonlinearities associated with the separation vortices from the leading edges and side edges of the lifting surfaces. The wing and tail characteristics are calculated using lifting surface theories which include effects of incidence, camber, twist, and induced velocities from external sources of disturbance such as bodies and vortices. The lifting surface theories calculate the distribution of leading edge and side edge suction which is converted to vortex lift using the Polhamus suction analogy. Correlation curves are developed to determine the fraction of the theoretical suction force which is converted into vortex lift. The prediction method is compared with experimental data on a variety of aircraft configurations to assess the accuracy and limitations of the method.

Mendenhall, M. R.↗

NASA NTRS1974

Optical image of a cometary nucleus: 1980 flyby of Comet Encke

The feasibility was investigated of obtaining optical images of a cometary nucleus via a flyby of Comet Encke. A physical model of the dust cloud surrounding the nucleus was developed by using available physical data and theoretical knowledge of cometary physics. Using this model and a Mie scattering code, calculations were made of the absolute surface brightness of the dust in the line of sight of the on-board camera and the relative surface brightness of the dust compared to the nucleus. The brightness was calculated as a function of heliocentric distance and for different phase angles (sun-comet-spacecraft angle).

Wells, W. C.↗

NASA NTRS1976

A study of a sector spectrophotometer and auroral O+(2P-2D) emissions

The metastable O+(2P-2D) auroral emission was investigated. The neighboring OH contaminants and low intensity levels of the emission itself necessitated the evolution of an instrument capable of separating the emission from the contaminants and having a high sensitivity in the wavelength region of interest. A new type of scanning photometer was developed and its properties are discussed. The theoretical aspects of auroral electron interaction with atomic oxygen and the resultant O+(2P-2D) emissions were examined in conjunction with N2(+)1NEG emissions. Ground based measurements of O+(2P-2D) auroral emission intensities were made using the spatial scanning photometer (sector spectrophotometer). Simultaneous measurements of N2(+)1NEG sub 1,0 emission intensity were made in the same field of view using a tilting photometer. Time histories of the ratio of these two emissions made in the magnetic zenith during auroral breakup periods are given. Theories of I sub 7319/I sub 4278 of previous investigators were presented. A rocket measurement of N2(+)1NEG sub 0,0 and O+(2P-2D) emission in aurora was examined in detail and was found to agree with the ground based measurements. Theoretical examination resulted in the deduction of the electron impact efficiency generating O+(2P) and also suggests a large source of O+(2P) at low altitude. A possible source is charge exchange of N+(1S) with OI(3P).

Swenson, G. R.↗

NASA NTRS1976

Modeling laser velocimeter signals as triply stochastic Poisson processes

Previous models of laser Doppler velocimeter (LDV) systems have not adequately described dual-scatter signals in a manner useful for analysis and simulation of low-level photon-limited signals. At low photon rates, an LDV signal at the output of a photomultiplier tube is a compound nonhomogeneous filtered Poisson process, whose intensity function is another (slower) Poisson process with the nonstationary rate and frequency parameters controlled by a random flow (slowest) process. In the present paper, generalized Poisson shot noise models are developed for low-level LDV signals. Theoretical results useful in detection error analysis and simulation are presented, along with measurements of burst amplitude statistics. Computer generated simulations illustrate the difference between Gaussian and Poisson models of low-level signals.

Mayo, W. T., Jr.↗

NASA NTRS1978

NASA Agricultural Aircraft Research Program in the Langley Vortex Research Facility and the Langley Full Scale Wind Tunnel

The current status of aerial applications technology research at the Langley's Vortex Research Facility and Full-Scale Wind Tunnel is reviewed. Efforts have been directed mainly toward developing and validating the required experimental and theoretical research tools. A capability to simulate aerial dispersal of materials from agricultural airplanes with small-scale airplane models, numerical methods, and dynamically scaled test particles was demonstrated. Tests on wake modification concepts have proved the feasibility of tailoring wake properties aerodynamically to produce favorable changes in deposition and to provide drift control. An aerodynamic evaluation of the Thrush Commander 800 agricultural airplane with various dispersal systems installed is described. A number of modifications intended to provide system improvement to both airplane and dispersal system are examined, and a technique for documenting near-field spray characteristics is evaluated.

Jordan, F. L., Jr.↗

NASA NTRS1978

Effects of moisture profiles and laminate configuration on the hygro stress in advanced composites

A theoretical investigation was performed using a recently developed integrated theory for predicting the hygrothermomechanical response to investigate the effects of three different moisture profiles on the ply hygro stresses in angleplied laminates. The moisture profiles were linear, parabolic and hyperbolic varying from 1 percent at the exposed ply to '0' percent in the protected ply. The angleplied laminates were of two generic configurations. The results obtained are summarized graphically to illustrate the effects of both moisture profile and laminate configuration.

Chamis, C. C.↗

NASA NTRS1979

Polarization and scattering characteristics in the atmospheres of earth, Venus, and Jupiter

Our understanding of atmospheric scattering phenomena has increased through the combined developments of new electro-optical instrumentation, theoretical solutions for complex model atmospheres, and large computers enabling computation of such solutions. Earth satellites permit external, planetwide observations of our atmosphere, while spacecraft permit detailed measurements of the scattering by other planetary atmospheres. Some recent results are: elucidation of the effects of ozone absorption and high-altitude aerosol scattering on twilight colors and polarization; identification of a cloudbow on Venus and consequent deduction of the cloud particle shape, size distribution, and refractive index; and, the interpretation of Rayleigh scattering on Jupiter in terms of cloud-top topography.

Coffeen, D. L.↗

NASA NTRS1980

A microprocessor based high speed packet switch for satellite communications

The architectures of a single processor, a three processor, and a multiple processor system are described. The hardware circuits, and software routines required for implementing the three and multiple processor designs are presented. A bit-slice microprocessor was designed and microprogrammed. Maximum throughput was calculated for all three designs. Queue theoretic models for these three designs were developed and utilized to obtain analytical expressions for the average waiting times, overall average response times and average queue sizes. From these expressions, graphs were obtained showing the effect on the system performance of a number of design parameters.

Arozullah, M.↗

NASA NTRS1983

Algorithms for real-time flutter identification

The work reported here addresses the important algorithm issues necessary to achieve a real-time flutter monitoring system; namely, the guidelines for choosing appropriate model forms, reduction of the parameter convergence transient, handling multiple modes, the effect of overparameterization, and estimate accuracy predictions, both online and for experiment design. An approach for efficiently computing continuous-time flutter parameter Cramer-Rao estimate error bounds has been developed. This enables a convincing comparison of theoretical and simulation results, as well as off-line studies in preparation for a flight test. Theoretical predictions, simulation and flight test results from the NASA/Dryden Drones for Aerodynamic and Structural Test (DAST) Program are compared.

Walker, R. A.↗

NASA NTRS1982

Theoretical studies in isoelectric focusing

A mathematical model has been developed which describes the steady state in an isoelectric focusing (IEF) system with ampholytes or monovalent buffers. The model is based on the fundamental equations describing the component dissociation equilibria, mass transport due to diffusion and electromigration, electroneutrality, and the conservation of charge. The validity and usefulness of the model has been confirmed by using it to formulate buffer systems in actual laboratory experiments. The model has been recently extended to include the evolution of transient states not only in IEF but also in other modes of electrophoresis.

Mosher, R. A.↗

NASA NTRS1983

Rotor-vortex interaction noise

A theoretical and experimental study was conducted to develop a validated first principles analysis for predicting noise generated by helicopter main-rotor shed vortices interacting with the tail rotor. The generalized prediction procedure requires a knowledge of the incident vortex velocity field, rotor geometry, and rotor operating conditions. The analysis includes compressibility effects, chordwise and spanwise noncompactness, and treats oblique intersections with the blade planform. Assessment of the theory involved conducting a model rotor experiment which isolated the blade-vortex interaction noise from other rotor noise mechanisms. An isolated tip vortex, generated by an upstream semispan airfoil, was convected into the model tail rotor. Acoustic spectra, pressure signatures, and directivity were measured. Since assessment of the acoustic prediction required a knowledge of the vortex properties, blade-vortes intersection angle, intersection station, vortex stength, and vortex core radius were documented. Ingestion of the vortex by the rotor was experimentally observed to generate harmonic noise and impulsive waveforms.

Schlinker, R. H.↗

NASA NTRS1984

Real-time flutter analysis

The important algorithm issues necessary to achieve a real time flutter monitoring system; namely, the guidelines for choosing appropriate model forms, reduction of the parameter convergence transient, handling multiple modes, the effect of over parameterization, and estimate accuracy predictions, both online and for experiment design are addressed. An approach for efficiently computing continuous-time flutter parameter Cramer-Rao estimate error bounds were developed. This enables a convincing comparison of theoretical and simulation results, as well as offline studies in preparation for a flight test. Theoretical predictions, simulation and flight test results from the NASA Drones for Aerodynamic and Structural Test (DAST) Program are compared.

Walker, R.↗

NASA NTRS1983

ECUT: Energy Conversion and Utilization Technologies program. Heterogeneous catalysis modeling program concept

Insufficient theoretical definition of heterogeneous catalysts is the major difficulty confronting industrial suppliers who seek catalyst systems which are more active, selective, and stable than those currently available. In contrast, progress was made in tailoring homogeneous catalysts to specific reactions because more is known about the reaction intermediates promoted and/or stabilized by these catalysts during the course of reaction. However, modeling heterogeneous catalysts on a microscopic scale requires compiling and verifying complex information on reaction intermediates and pathways. This can be achieved by adapting homogeneous catalyzed reaction intermediate species, applying theoretical quantum chemistry and computer technology, and developing a better understanding of heterogeneous catalyst system environments. Research in microscopic reaction modeling is now at a stage where computer modeling, supported by physical experimental verification, could provide information about the dynamics of the reactions that will lead to designing supported catalysts with improved selectivity and stability.

Voecks, G. E.↗

NASA NTRS1984

Study on spectral/radiometric characteristics of the Thematic Mapper for land use applications

An information theoretic measure of multispectral information content is developed and applied to a simultaneous LANDSAT TM and MSS data set. The entropy based function measures the dispersion and concentration of signal values in various data spaces, irrespective of specific class memberships. It is used to compare the information content of TM and MSS and of various subsets of TM and MSS bans, as well as tasseled cap transformations of the band values. Differences exist between the information measure results and results using variance based measures. System design information capacities and data space volumes are also compared. The results and observations presented are considered preliminary in nature since only one real and one simulated data set are analyzed.

Malila, W. A.↗

NASA NTRS1985

A comparison of experimental and theoretical results for rotordynamic coefficients of four annular gas seals

The test facility and initial test program developed to experimentally measure the fluid forces induced by annular gas seals is described. A comparison of theoretically predicted and experimentally obtained data for smooth and honeycomb seals is provided. And a comparison of experimental data from the tests of three smooth-rotor/smooth-stator seals is provided. The leakage of the working fluid through the seal, the pressure gradient along the seal length, entrance pressure-loss data, and rotordynamic coefficients provide a basis for comparison. A short discussion on seal theory is included, and various rotordynamic coefficient identification schemes are described.

Childs, D. W.↗