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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 901 records · Page 50
All sourcesNASA NTRSDOE OSTI
NASA NTRS1971

Thermodynamic properties of carbon in b.c.c. and f.c.c. iron-silicon-carbon solid solutions.

The equilibrium between hydrogen-methane gas mixtures and Fe-Si-C solid solutions has been investigated both as a function of temperature and carburizing gas composition. The thermodynamic properties of the carbon atoms in both b.c.c. and f.c.c. solid solution have been derived from the equilibrium measurements. The results found have been compared with those of earlier investigations and with the predictions of recent theoretical models on ternary solid solutions containing both substitutional and interstitial solute atoms.

Chraska, P.↗
NASA NTRS1973

Optical scattering properties of Saturn's ring.

Reliable data defining the photometric function of the Saturn ring system at visual (V) wavelengths are interpreted in terms of a simple scattering model. To facilitate the analysis, new photographic photometry of the ring has been carried out utilizing the Lowell observatory plate collection. Homogeneous measurements of the mean surface brightness (rings A and B together), covering almost the complete range in planetocentric solar declination angle, are presented. The ring model adopted is a plane-parallel slab of isotropically scattering particles; the single scattering albedo and the perpendicular optical thickness are both arbitrary. Results indicate that primary scattering is inadequate to describe the photometric properties of the ring; multiple scattering predominates for all angles of tilt with respect to the Sun and Earth.

Price, M. J.↗
NASA NTRS2000

Wavelet and Fractal Analysis of Remotely Sensed Surface Temperature with Applications to Estimation of Surface Sensible Heat Flux Density

Wavelet and fractal analyses have been used successfully to analyze one-dimensional data sets such as time series of financial, physical, and biological parameters. These techniques have been applied to two-dimensional problems in some instances, including the analysis of remote sensing imagery. In this respect, these techniques have not been widely used by the remote sensing community, and their overall capabilities as analytical tools for use on satellite and aircraft data sets is not well known. Wavelet and fractal analyses have the potential to provide fresh insight into the characterization of surface properties such as temperature and emissivity distributions, and surface processes such as the heat and water vapor exchange between the surface and the lower atmosphere. In particular, the variation of sensible heat flux density as a function of the change In scale of surface properties Is difficult to estimate, but - in general - wavelets and fractals have proved useful in determining the way a parameter varies with changes in scale. We present the results of a limited study on the relationship between spatial variations in surface temperature distribution and sensible heat flux distribution as determined by separate wavelet and fractal analyses. We analyzed aircraft imagery obtained in the thermal infrared (IR) bands from the multispectral TIMS and hyperspectral MASTER airborne sensors. The thermal IR data allows us to estimate the surface kinetic temperature distribution for a number of sites in the Midwestern and Southwestern United States (viz., San Pedro River Basin, Arizona; El Reno, Oklahoma; Jornada, New Mexico). The ground spatial resolution of the aircraft data varied from 5 to 15 meters. All sites were instrumented with meteorological and hydrological equipment including surface layer flux measuring stations such as Bowen Ratio systems and sonic anemometers. The ground and aircraft data sets provided the inputs for the wavelet and fractal analyses, and the validation of the results.

Schieldge, John↗
NASA NTRS1986

A system of three-dimensional complex variables

Some results of a new theory of multidimensional complex variables are reported, including analytic functions of a three-dimensional (3-D) complex variable. Three-dimensional complex numbers are defined, including vector properties and rules of multiplication. The necessary conditions for a function of a 3-D variable to be analytic are given and shown to be analogous to the 2-D Cauchy-Riemann equations. A simple example also demonstrates the analogy between the newly defined 3-D complex velocity and 3-D complex potential and the corresponding ordinary complex velocity and complex potential in two dimensions.

Martin, E. Dale↗
NASA NTRS2023

Modeling Sea Ice Albedo and Transmittance Measurements With A Fully-Coupled Radiative Transfer Model

A rigorous treatment of the sea ice medium has been incorporated in the advanced Coupled Ocean-Atmosphere Radiative Transfer (COART) model. The inherent optical properties (IOPs) of brine pockets and air bubbles over the 0.25-4.0 μm spectral region are parameterized as a function of the vertical profile of the sea ice physical properties (temperature, salinity and density). We test the model performance using available albedo and transmittance measurements collected during the Impacts of Climate on the Ecosystems and Chemistry of the Arctic Pacific Environment (ICESCAPE) and the Surface Heat Budget of the Arctic Ocean (SHEBA) field campaigns. The observations are adequately simulated when at least three layers are used to represent bare (first-year and multi-year) ice, including a thin top layer characterized by low density and high scattering. Two layers can be sufficient to model isolated cases of multi-year ice, and apply well to ponded ice except for shallow ponds over thick ice. The albedo and transmittance of ponded ice in the visible are mainly determined by the optical properties of the ice underlying the water layer used to model the pond. Sensitivity results indicate that the air volume or ice density has the largest impact on the simulated fluxes. Possible contamination from light-absorbing impurities, such as black carbon or ice algae, is also implemented in the model and is able to effectively reduce the albedo and transmittance in the visible spectrum to further improve the model-observation agreement. The agreement between the observed and modeled spectra validates the parameterization of the sea ice IOPs, and endorses COART as an accurate tool for radiation studies in the cryosphere.

Coupled Ocean-9 Atmosphere Radiative Transfer (COA↗
NASA NTRS2011

Solar Wind Strahl Observations and Their Implication to the Core-Halo Formation due to Scattering

A study of the kinetic properties of the strahl electron velocity distribution functions (VDF?s) in the solar wind is presented. This study focuses on the mechanisms that control and regulate the electron VDF?s and the stability of the strahl electrons in the solar wind; mechanisms that are not yet well understood. Various parameters are investigated such as the strahl-electron density, temperature anisotropy, and electron heat-flux. These parameters are used to investigate the stability of the strahl population. The analysis check for whether the strahl electrons are constrained by some instability (e.g., the whistler or KAW instabilities), or are maintained by other types of processes. The electron heat-flux and temperature anisotropy are determined by modeling of the 3D-VDF?s from which the moments properties of the various populations are obtained. The results of this study have profound implication on the current hypothesis about the probable formation of the solar wind halo electrons produced from the scattering of the strahl population. This hypothesis is strengthened by direct observations of the strahl electrons being scattered into the core-halo in an isolated event. The observation implies that the scattering of the strahl is not a continuous process but occurs in bursts in regions where conditions for wave growth providing the scattering are optimum. Sometimes, observations indicate that the strahl component is anisotropic (Tper/Tpal approx. 2). This provides a possible free energy source for the excitation of whistler waves as a possible scattering mechanism, however this condition is not always observed. The study is based on high time resolution data from the Cluster/PEACE electron spectrometer.

Vinas, Adolfo F.↗
NASA NTRS1991

Optical properties of aggregate particles whose outer diameter is comparable to the wavelength

Results are described of numerical calculations of the optical properties (extinction efficiency, single-scattering albedo, phase function, and linear polarization) of aggregate particles whose outer diameter is comparable with the wavelength. Results are presented for two types of particle, one composed of monomers whose radius is small compared with the wavelength and a second containing monomers with larger radii. The shape of the forward-scattered lobe of the phase function is diagnostic of the mean projected area (but differs from that for an equal-area sphere), while the linear polarization, phase function at large scattering angles, and single-scattering albedo depend on the monomer diameter. The wavelength dependence of the extinction efficiency differs markedly from that for equal-area spheres. These results can be used to infer particle properties from remotely sensed data.

West, Robert A.↗
NASA NTRS1978

Scattering of light from particulate surfaces. I - A laboratory assessment of multiple-scattering effects

In planetary applications it is sometimes important to know the degree to which multiple scattering is influencing the photometric properties of a surface. An investigation is conducted concerning the point at which the single-scattering approximation used in the theory developed by Hapke (1963) and Irvine (1966) breaks down. It is shown that the Hapke-Irvine photometric function provides an adequate representation of the scattering properties of particulate surfaces whose geometric albedos (or normal reflectances) do not exceed 0.3. An experiment is conducted to estimate the normal reflectance below which the Hapke-Irvine equation considered provides an adequate representation of the scattering properties of a particulate surface. The investigation makes use of a set of samples which were prepared by mixing magnesium oxide and charcoal powders. The samples have a range in normal reflectance from 0.04 to 1.04.

Veverka, J.↗
NASA NTRS1987

Robustness issues in boundary feedback of flexible structures

Transfer function models for basic structural elements with boundary control reveal certain inherent properties relevant to questions of control system realization, design, and analysis of robustness. The transfer functions involved are not strictly proper, may be nonminimum phase (except for the special case of colocated actuation and sensing), and often have large number of poles on the imaginary axis. In this paper these basic questions are considered in terms of modeling and control system design for robustness. The application of algebraic methods for computing stabilizing control, based on certain exact, irrational transfer functions is investigated. Boundary control of the wave equation is considered and extension of the method to more general problems is suggested. Special attention is given to implementation issues associated with a class of infinite dimensional control laws.

Bennett, W. H.↗
NASA NTRS1988

On hierarchical solutions to the BBGKY hierarchy

It is thought that the gravitational clustering of galaxies in the universe may approach a scale-invariant, hierarchical form in the small separation, large-clustering regime. Past attempts to solve the Born-Bogoliubov-Green-Kirkwood-Yvon (BBGKY) hierarchy in this regime have assumed a certain separable hierarchical form for the higher order correlation functions of galaxies in phase space. It is shown here that such separable solutions to the BBGKY equations must satisfy the condition that the clustered component of the solution has cluster-cluster correlations equal to galaxy-galaxy correlations to all orders. The solutions also admit the presence of an arbitrary unclustered component, which plays no dyamical role in the large-clustering regime. These results are a particular property of the specific separable model assumed for the correlation functions in phase space, not an intrinsic property of spatially hierarchical solutions to the BBGKY hierarchy. The observed distribution of galaxies does not satisfy the required conditions. The disagreement between theory and observation may be traced, at least in part, to initial conditions which, if Gaussian, already have cluster correlations greater than galaxy correlations.

Hamilton, A. J. S.↗
NASA NTRS1995

Exponentially accurate approximations to piece-wise smooth periodic functions

A family of simple, periodic basis functions with 'built-in' discontinuities are introduced, and their properties are analyzed and discussed. Some of their potential usefulness is illustrated in conjunction with the Fourier series representations of functions with discontinuities. In particular, it is demonstrated how they can be used to construct a sequence of approximations which converges exponentially in the maximum norm to a piece-wise smooth function. The theory is illustrated with several examples and the results are discussed in the context of other sequences of functions which can be used to approximate discontinuous functions.

Greer, James↗
NASA NTRS2001

Structure and Variability of Water Vapor in the Upper Troposphere and Lower Stratosphere

Upper-tropospheric humidity (UTH) has been synoptically mapped via an algorithm that rejects small-scale undersampled variance, which is intrinsic to asymptotic measurements of water vapor, cloud, and other convective properties. Mapped distributions of UTH have been used, jointly with high-resolution Global Cloud Imagery (GCI), to study how the upper troposphere is humidified. The time-mean distribution of UTH is spatially correlated to the time-mean distribution of cold cloud fraction (eta)(sub c) (T < than 230 K). Regions of large UTH coincide with regions of large eta(sub c), which mark deep convection. They also coincide with regions of reduced vertical stability, in which the vertical gradient of theta is weakened by convective mixing. Coldest cloud cover is attended convective overshoots above the local tropopause, which is simultaneously coldest and highest. Together, these features reflect the upper-troposphere being ventilated by convection, which mixes in moist air from lower levels. Histograms of UTH and eta(sub c) have been applied to construct the joint probability density function, which quantifies the relationship between these properties. The expected value of UTH in convective regions is strongly correlated to the expected value of eta(sub c). In ensembles of asymptotic samples, the correlation between epsilon[UTH] and epsilon[eta(sub c)] exceeds 0.80. As these expectations reflect the most likely values, the strong correlation between epsilon[UTH] and epsilon[eta(sub c)] indicates that the large-scale organization of UTH is strongly shaped by convective pumping of moisture from lower levels. The same relationship holds for unsteady fields - even though, instantaneously, those fields are comprised almost entirely of small-scale convective structure. The spatial autocorrelation of UTH, constructed at high resolution from overpass data along ascending and descending tracks of the orbit, is limited to only a couple of degrees in the horizontal. This mirrors the spatial autocorrelation of eta(sub c), which likewise operates coherently on short scales. The short correlation scale of UTH, which reflects the scale of individual convective systems, is comparable to the spacing of retrievals from MLS. These scales are undersampled in the asynoptic measurements. Despite their prevalence, the mapping algorithm described above successfully recovers synoptic behavior operating coherently on large scales. It reveals eastward migration of anomalous UTH from the Indian ocean to the central Pacific, in association with the modulation of convection by the Madden-Julian oscillation. Additional information is contained in the original extended abstract.

Salby, Murry L.↗
NASA NTRS1998

Radar Studies in the Solar System

We aid in study of the solar system by means of ground-based radar. We have concentrated on: (1) developing the ephemerides needed to acquire radar data at Arecibo Observatory and (2) analyzing the resultant data to: test fundamental laws of gravitation; determine the size , shape, topography, and spin vectors of the targets; and study the surface properties of these objects, through their scattering law and polarization characteristics. We are engaged in radar observations of asteroids and comets, both as systematically planned targets and as "targets of opportunity." In the course of the program, we have prepared ephemerides for about 80 asteroids and three comets, and the radar observations have been made or attempted at the Arecibo Observatory, in most cases successfully, and in some cases on more than one apparition. The results of these observations have included echo spectra for the targets and, in some cases, delay - Doppler images and measurements of the total round-trip delay to the targets. Perhaps the most dramatic of these results are the images obtained for asteroids (4179) Toutatis and 1989PB (Castalia), which were revealed to be double-lobed objects by the radar images. Besides these direct results, the radar observations have furnished information on the sizes and shapes of the targets through analysis of the Doppler width of the echoes as a function of time, and on the surface properties (such as composition, bulk density, and roughness) through analysis of the reflectivity and of the polarization state of the echoes. We have also refined the orbits of the observed asteroids as a result of the Doppler (and in some cases delay) measurements from the radar observations. Although the orbits of main-belt asteroids accessible to ground-based radar are quite well known from the available optical data, some near-Earth objects have been seen by radar very soon after their optical discovery (for example, 199OMF, just eight days after discovery). In such cases. the radar results ensure that the object in question can be anticipated and identified at the next apparition. We have also participated in radar studies of the terrestrial planets. The results of these studies have included both planetary topography profiles from the analysis of round-trip delays to points along the target Doppler equator and determinations of the target spin state. The latter is of special interest in the case of Venus, which is very close to, but not on, a multi-body spin-orbit resonance such that Venus rotates 12 times for every 8 Earth orbits and 13 Venus orbits. As a result, Venus presents nearly the same face toward Earth at each inferior conjunction. Our latest results confirm that the spin state of Venus is slightly off the resonance. The delay measurements from planetary 2 ranging have also been used in combination with other types of range data in testing general relativity with increasing accuracy. We have also been engaged in radar studies of planetary satellites. Using our ephemerides, Arecibo made radar observations of the Galilean satellites of Jupiter and of Mars' satellite Phobos during the favorable opposition seasons (1988-1992 for Jupiter and 1990 for Mars). An attempt was also made to observe Deimos, but without detecting an echo. In 1997, an attempt was made to observe Saturn's satellite Titan, using the newly upgraded Arecibo radar system for transmitting and the Goldstone radar for receiving, but no echo was detected. The study of satellites by radar is in many ways similar to that of asteroids. The results from these observations have included characterization of the surface properties from the reflectivity and polarization ratio, as well as (in the case of the large satellites of Jupiter) the variation of reflectivity with incidence angle.

Shaprio, Irwin I.↗
NASA NTRS2019

Charactarization of Thermal Protection Systems

In 2012, NASA's mission of landing the Mars Science Laboratory (MSL) on Mars was successful. MSL was protected by an ablative heatshield of tiled low density material known as PICA (phenolic impregnated carbon ablator). The heatshield was instrumented with MEDLI (MSL Entry Descent Landing Instrument) a suite of sensors & thermocouples at discrete locations in order to monitor the in-depth ablator temperature response and surface pressure. MEDLI was designed and developed by NASA Langley, in partnership with NASA Ames Research Center for the purposes of probing Mars and evaluating the performance of the spacecraft upon entry into the Martian atmosphere. The flight data reduces the uncertainty in engineer models for predicting the response of a spacecraft towards the extreme heating environment of an entry into the Martian atmosphere. MEDLI2 is a part of the Mars 2020 mission and is the next-generation sensor suite for entry, descent, and landing. This data will again help engineers validate their flight models. Additionally, the atmospheric data, can help us understand atmospheric density and winds. This is a critical study for reducing risks to both robotic and future human missions to Mars. Engineered models for Mars 2020 are dependent upon parameters related to the materials response to heating and radiation. In this work, the thermal properties and other measurements of various ablative materials are analyzed to achieve greater utility of the 2012 MEDLI flight data and more accurately determine the parameters being used in Mars 2020. The purpose of this study was to measure specific heat, thermal conductivity, char yield, reflectance as a function of wavelength, and other thermal parameters and optical properties of various ablative materials. CO2(g) at extreme temperatures emits radiation impacting MEDLI2 flight predictions. Emissivity & absorptivity as a function of temperature were calculated from FTIR and UV-Vis data as a means of investigating whether these materials might absorb CO2 radiation upon entry into the Mars atmosphere.

HEEET↗
NASA NTRS2001

Thermal Infrared Spectral Band Detection Limits for Unidentified Surface Materials

Infrared emission spectra recorded by airborne or satellite spectrometers can be searched for spectral features to determine the composition of rocks on planetary surfaces. Surface materials are identified by detections of characteristic spectral bands. We show how to define whether to accept an observed spectral feature as a detection when the target material is unknown. We also use remotely sensed spectra measured by the Thermal Emission Spectrometer (TES) and the Spatially Enhanced Broadband Array Spectrograph System to illustrate the importance of instrument parameters and surface properties on band detection limits and how the variation in signal-to-noise ratio with wavelength affects the bands that are most detectable for a given instrument. The spectrometer's sampling interval, spectral resolution, signal-to-noise ratio as a function of wavelength, and the sample's surface properties influence whether the instrument can detect a spectral feature exhibited by a material. As an example, in the 6-13 micrometer wavelength region, massive carbonates exhibit two bands: a very strong, broad feature at approximately 6.5 micrometers and a less intense, sharper band at approximately 11.25 micrometers. Although the 6.5-micrometer band is stronger and broader in laboratory-measured spectra, the 11.25-micrometer band will cause a more detectable feature in TES spectra.

Kirkland, Laurel E.↗
NASA NTRS2023

Simulated Inherent Optical Properties of Aquatic Particles Using the Equivalent Algal Populations (EAP) Model

Paired measurements of phytoplankton absorption and backscatter, the inherent optical properties central to the interpretation of ocean colour remote sensing data, are notoriously rare. We present a dataset of Chlorophyll a (Chl a) -specific phytoplankton absorption, scatter and backscatter for 17 different phytoplankton groups, derived from first principles using measured in vivo pigment absorption and a well-validated semi-analytical coated sphere model which simulates the full suite of biophysically consistent phytoplankton optical properties. The optical properties of each simulated phytoplankton cell are integrated over an entire size distribution and are provided at high spectral resolution. The model code is additionally included to enable user access to the complete set of wavelength-dependent, angularly resolved volume scattering functions. This optically coherent dataset of hyperspectral optical properties for a set of globally significant phytoplankton groups has potential for use in algorithm development towards the optimal exploitation of the new age of hyperspectral satellite radiometry.

Equivalent Algal Populations↗
NASA NTRS1987

Impact of thermal energy storage properties on solar dynamic space power conversion system mass

A 16 parameter solar concentrator/heat receiver mass model is used in conjunction with Stirling and Brayton Power Conversion System (PCS) performance and mass computer codes to determine the effect of thermal energy storage (TES) material property changes on overall PCS mass as a function of steady state electrical power output. Included in the PCS mass model are component masses as a function of thermal power for: concentrator, heat receiver, heat exchangers (source unless integral with heat receiver, heat sink, regenerator), heat engine units with optional parallel redundancy, power conditioning and control (PC and C), PC and C radiator, main radiator, and structure. Critical TES properties are: melting temperature, heat of fusion, density of the liquid phase, and the ratio of solid-to-liquid density. Preliminary results indicate that even though overalll system efficiency increases with TES melting temperature up to 1400 K for concentrator surface accuracies of 1 mrad or better, reductions in the overall system mass beyond that achievable with lithium fluoride (LiF) can be accomplished only if the heat of fusion is at least 800 kJ/kg and the liquid density is comparable to that of LiF (1880 kg/cu m.

Juhasz, Albert J.↗
NASA NTRS1987

Impact of thermal energy storage properties on solar dynamic space power conversion system mass

A 16 parameter solar concentrator/heat receiver mass model is used in conjunction with Stirling and Brayton Power Conversion System (PCS) performance and mass computer codes to determine the effect of thermal energy storage (TES) material property changes on overall PCS mass as a function of steady state electrical power output. Included in the PCS mass model are component masses as a function of thermal power for: concentrator, heat receiver, heat exchangers (source unless integral with heat receiver, heat sink, regenerator), heat engine units with optional parallel redundancy, power conditioning and control (PC and C), PC and C radiator, main radiator, and structure. Critical TES properties are: melting temperature, heat of fusion, density of the liquid phase, and the ratio of solid-to-liquid density. Preliminary results indicate that even though overall system efficiency increases with TES melting temperature up to 1400 K for concentrator surface accuracies of 1 mrad or better, reductions in the overall system mass beyond that achievable with lithium fluoride (LiF) can be accomplished only if the heat of fusion is at least 800 kJ/kg and the liquid density is comparable to that of LiF (1800 kg/cu m).

Juhasz, Albert J.↗