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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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NASA NTRS1991

Learning classification trees

Algorithms for learning classification trees have had successes in artificial intelligence and statistics over many years. How a tree learning algorithm can be derived from Bayesian decision theory is outlined. This introduces Bayesian techniques for splitting, smoothing, and tree averaging. The splitting rule turns out to be similar to Quinlan's information gain splitting rule, while smoothing and averaging replace pruning. Comparative experiments with reimplementations of a minimum encoding approach, Quinlan's C4 and Breiman et al. Cart show the full Bayesian algorithm is consistently as good, or more accurate than these other approaches though at a computational price.

Buntine, Wray↗
NASA NTRS1992

Final results of the Space Exposed Experiment Developed for Students (SEEDS) P-0004-2

Space Exposed Experiment Developed for Students (SEEDS), resulted in the distribution of over 132,000 SEED kits in 1990. The kits contained Rutger's tomato seeds that had flown on the Long Duration Exposure Facility (LDEF) as well as seeds that had been stored in a climate controlled warehouse for the same period of time. Students compared germination and growth rate characteristics of the two seeds groups and returned data to NASA for analysis. The scientific information gained was valuable as students shared the excitement of taking part in a national project. Of greater importance was the subsequent interest generated in science education.

Grigsby, Doris K.↗
NASA NTRS1992

Lidar multiple scattering: Dependence on atmospheric parameters

Backscatter lidars are very useful tools in gaining information about the atmosphere. Inversion of backscatter signals can be used to retrieve the spatial distribution of clouds and aerosols, e.g., vertical extensions of clouds and aerosol layers, detection of 'subvisible' cirrus, etc., very accurately compared to passive radiometers. To retrieve extinction coefficient profiles, in general, the so-called lidar equation is solved. This equation describes a laser pulse which propagates through an atmosphere with transmission exp(- integral of sigma(z')dz'), which is scattered singly under 180 degrees towards a receiver, and which is attenuated on its way back again by exp(- integral of sigma(z')dz'). For inversion, further information on optical properties of the scatterers are required (extinction to backscatter ratio). However, it is evident that, at least for optically thick clouds and/or large receiver's field-of-views, this approach may be erroneous because of multiply scattered photons. Several studies were performed to simulate multiple scattering in case of collimated beams or pulses including Monte Carlo, transport, and diffusion theory. Unfortunately, most of the approaches require an enormous amount of computer time. Thus, it is meaningful to elaborate approximate methods, and one such method is discussed. Our method is based on Bissonnett (1988). We have improved the numerical simulation of limited field-of-view detectors, and compared the results to Monte Carlo calculations and an exact model of Altmann (1989).

Wiegner, Matthias↗
NASA NTRS1991

The robotic exploration missions at Mars

A set of robotic missions to Mars are designed to provide information to enable the eventual human exploration of the planet. The strategy of the mission sequence including broad global assessments to specific site certification is described. The exploration and science information gained by each mission is discussed.

Cunningham, Glenn E.↗
NASA NTRS1992

Iterative refinement scheduling

We present a heuristics-based approach to deep space mission scheduling which is modeled on the approach used by expert human schedulers in producing schedules for planetary encounters. New chronological evaluation techniques are used to focus the search by using information gained during the scheduling process to locate, classify, and resolve regions of conflict. Our approach is based on the assumption that during the construction of a schedule there exist several disjunct temporal regions where the demand for one resource type or a single temporal constraint dominates (bottleneck regions). If the scheduler can identify these regions and classify them based on their dominant constraint, then the scheduler can select the scheduling heuristic.

Biefeld, Eric↗
NASA NTRS1993

Combustion experiments in reduced gravity with two-component miscible droplets

The combustion of liquid fuels is a topic worthy of scientific attention on practical and fundamental grounds. Most practical applications of liquid-fuel combustion involve the formation of spray diffusion flames, where droplets frequently burn in groups rather than individually. The combustion is typically complex, with interactions occurring between various physical mechanisms. Many efforts to understand liquid sprays have focused upon studying isolated droplets. Information gained from these studies is often not directly transferable to spray situations. However, isolated-droplet studies are useful in that they allow certain phenomena (e.g., extinction) to be studied under well-controlled and simplified conditions. When theory and experiment agree for simplified situations, predictions for more complex cases (where accurate experimental data may not exist) may be made with more confidence. The simplest droplet combustion scenario is that of an isolated droplet undergoing spherically-symmetric combustion in an environment of infinite extent. The idealization is approached only when forced and buoyant convection are negligible, the droplet is unsupported, and all foreign objects are far-removed from the combustion zone. Appreciable gravity levels compromise spherical symmetry by inducing buoyant convection.

Shaw, Benjamin D.↗
NASA NTRS1992

Coordination of multiwavelength groundbased and satellite observations of novae in outburst

Observational data on novae in outburst are reviewed, focusing on the information gained from ultraviolet spectroscopy. Topics discussed include a brief taxonomy of novae, the theoretical framework, observational diagnostics of the outburst, IUE satellite observations, and future trends in novae observations at many wavelengths using space-based observatories to augment the work of ground-based observers.

Shore, Steven N.↗
NASA NTRS1993

Assimilation of solids during ascent of magmas from the Bartoy Field of the Baikal Region, Siberia

Most investigators ascribe mare basalt magma genesis to partial melting at depths of approximately 130 to greater than 400 km within the cumulate pile deposited from a lunar magma ocean. Mare basalts share with mid-ocean ridge basalts the characteristic of relative depletion in LREE and other incompatible trace elements that arises from melting within 'used' mantle, from which crust-forming elements have already been separated. Some mare basalt types do not show the classical, La-Nd depleted mare basalt REE distributions; however, some types are isotopically heterogeneous. These differences have been ascribed to assimilation, mainly AFC-style, of KREEPy highland material overlying the source region. Might such assimilation occur during magma ascent through the KREEPy material? To gain information from a terrestrial setting on possible assimilation during ascent, we have studied a suite of Quaternary nepheline-hawalites and nepheline-mugearites from the Bartoy cinder cone complex of the Baikal Rift, Siberia. The Bartoy magmas originated from greater than 80 km deep, and erupted through thick Archean crust. We find evidence for assimilation of approximately 31 wt. percent xenocrysts of garnet, aluminous clinopyroxene, kaersutite, and olivine, all presumably from the basalt source region, but no appreciable assimilation of overlying crust, consistent with isotopic constraints. Magmatic superheat made available by rapid ascent and decomposition accounts adequately for the energy of assimilation; no accompanying fractional crystallization is required or evident.

Haas, Johnson R.↗
NASA NTRS1993

Microphysical properties of the November 26 cirrus cloud retrieved by Doppler radar/IR radiometer technique

Gaining information about cirrus cloud microphysics requires development of remote sensing techniques. In an earlier paper. Matrosov et al. (1992) proposed a method to estimate ice water path (IWP) (i.e., vertically integrated ice mass content IMC) and characteristic particle size averaged through the cloud from combined groundbased measurements of radar reflectivities and IR brightness temperatures of the downwelling thermal radiation in the transparency region of 10-12 mu m. For some applications, the vertically averaged characteristic particle sizes and IWP could be the appropriate information to use. However, vertical profiles of cloud microphysical parameters can provide a better understanding of cloud structure and development. Here we describe a further development of the previous method by Matrosov et al. (1992) for retrieving vertical profiles of cirrus particle sizes and IMC rather than their vertically averaged values. In addition to measurements of radar reflectivities, the measurements of Doppler velocities are used in the new method. This provides us with two vertical profiles of measurements to infer two vertical profiles of unknowns, i.e., particle characteristic sizes and IMC. Simultaneous measurements of the IR brightness temperatures are still needed to resolve an ambiguity in particle size-fall velocity relationships.

Matrosov, Sergey Y.↗
NASA NTRS1993

Impact of LDEF photovoltaic experiment findings upon spacecraft solar array design and development requirements

Photovoltaic cells (solar cells) and other solar array materials were flown in a variety of locations on the Long Duration Exposure Facility (LDEF). With respect to the predicted leading edge, solar array experiments were located at 0 degrees (row 9), 30 degrees (row 8) and 180 degrees (row 3). Postflight estimates of location of the experiments with respect to the velocity vector add 8.1 degrees to these values. Experiments were also located on the Earth end of the LDEF longitudinal axis. Types and magnitudes of detrimental effects differ between the locations with some commonality. Postflight evaluation of the solar array experiments reveal that some components/materials are very resistant to the environment to which they were exposed while others need protection, modification, or replacement. Interaction of materials with atomic oxygen (AO), as an area of major importance, was dramatically demonstrated by LDEF results. Information gained from the LDEF flight allows array developers to set new requirements for on-going and future technology and flight component development.

Young, Leighton E.↗
NASA NTRS1993

The importance of environmental conditions in reflectance spectroscopy of laboratory analogs for Mars surface materials

Reflectance spectra are presented here for a variety of particulate, ferric-containing analogs to Martian soil (Fe(3+)-doped smectites and palagonites) to facilitate interpretation of remotely acquired spectra. The analog spectra were measured under differing environmental conditions to evaluate the influence of exposure history on water content and absorption features due to H2O in these samples. Each of these materials contains structural OH bonded to metal cations, adsorbed H2O, and bound H2O (either in a glass, structural site, or bound to a cation). Previous experiments involving a variety of Mars analogs have shown that the 3 micron H2O band in spectra of palagonites is more resistant to drying than the 3 micron H2O band in spectra of montmorillonites. Other experiments have shown that spectra of ferrihydrite and montmorillonites doped with ferric sulfate also contain sufficient bound H2O to retain a strong 3 micron band under dry conditions. Once the effects of the environment on bound water in clays, oxides, and salts are better understood, the hydration bands measured via reflectance spectroscopy can be used to gain information about the chemical composition and moisture content of real soil systems. Such information would be especially useful in interpreting observations of Mars where subtle spatial variations in the strengths of metal-OH and H2O absorptions have been observed in telescopic and ISM spectra. We measured bidirectional reflectance spectra of several Mars soil analogs under controlled environmental conditions to assess the effects of moisture content on the metal-OH and H2O absorptions. The samples analyzed include chemically altered montmorillonites, ferrihydrite. and palagonites from Hawaii and Iceland. Procedures for preparation of the cation-exchanged montmorillonites, ferric-salt doped montmorillonites, and ferric oxyhydroxides are described in detail elsewhere.

Bishop, J.↗
NASA NTRS1993

Martian deltas: Morphology and distribution

Recent detailed mapping has revealed numerous examples of Martian deltas. The location and morphology of these deltas are described. Factors that contribute to delta morphology are river regime, coastal processes, structural stability, and climate. The largest delta systems on Mars are located near the mouths of Maja, Maumee, Vedra, Ma'adim, Kasei, and Brazos Valles. There are also several smaller-scale deltas emplaced near channel mouths situated in Ismenius Lacus, Memnonia, and Arabia. Delta morphology was used to reconstruct type, quantity, and sediment load size transported by the debouching channel systems. Methods initially developed for terrestrial systems were used to gain information on the relationships between Martian delta morphology, river regime, and coastal processes.

Rice, J. W., Jr.↗
NASA NTRS1993

Production of long-term global water vapor and liquid water data set using ultra-fast methods to assimilate multi-satellite and radiosonde observations

During the next decade, many programs and experiments under the Global Energy and Water Cycle Experiment (GEWEX) will utilize present day and future data sets to improve our understanding of the role of moisture in climate, and its interaction with other variables such as clouds and radiation. An important element of GEWEX will be the GEWEX Water Vapor Project (GVaP), which will eventually initiate a routine, real-time assimilation of the highest quality, global water vapor data sets including information gained from future data collection systems, both ground and space based. The comprehensive global water vapor data set being produced by METSAT Inc. uses a combination of ground-based radiosonde data, and infrared and microwave satellite retrievals. This data is needed to provide the desired foundation from which future GEWEX-related research, such as GVaP, can build. The first year of this project was designed to use a combination of the best available atmospheric moisture data including: radiosonde (balloon/acft/rocket), HIRS/MSU (TOVS) retrievals, and SSM/I retrievals, to produce a one-year, global, high resolution data set of integrated column water vapor (precipitable water) with a horizontal resolution of 1 degree, and a temporal resolution of one day. The time period of this pilot product was to be det3ermined by the availability of all the input data sets. January 1988 through December 1988 were selected. In addition, a sample of vertically integrated liquid water content (LWC) was to be produced with the same temporal and spatial parameters. This sample was to be produced over ocean areas only. Three main steps are followed to produce a merged water vapor and liquid water product. Input data from Radiosondes, TOVS, and SSMI/I is quality checked in steps one and two. Processing is done in step two to generate individual total column water vapor and liquid water data sets. The third step, and final processing task, involves merging the individual output products to produce the integrated water vapor product. A final quality control is applied to the merged data sets.

Vonderhaar, T. H.↗
NASA NTRS1994

UV extinction and IR emission in diffuse H2 regions

HII regions occupy a unique position in our understanding of the physical relationships between stars, the interstellar medium, and galactic structure. Observations show a complex interaction between a newly formed hot star and its surroundings. In particular, the ultraviolet radiation from the stars modifies the pre-existing dust, which again affects both the amount of ionizing radiation absorbed by the gas, and the infrared spectrum emitted by the heated dust. The aim of this project was to use UV and far-UV observations to gain information on the nebular dust, and to use this dust to model the far-IR emission, for a consistent picture of a few selected diffuse HII regions. Using archival data from the IUE and Voyager data banks and computed model atmospheres, we have deduced extinction curves for early-types stars. The requisite spectral resolution turned out to be a major task. We have successfully modelled these curves in terms of a multi-component, multi-size distribution of dust grains, and interpret the differences in the curves as primarily due to the presence or non-presence of intermediate size grains (0.01 to 0.04 micron). Much smaller (0.005 micron) grains must also be present. Finally, we have made calculations of the temperature fluctuations and the corresponding infra-red emission in such small grains.

Aannestad, Per A.↗
NASA NTRS1994

Deriving a dosage-response relationship for community response to high-energy impulsive noise

The inability to systematically predict community response to exposure to sonic booms (and other high energy impulsive sounds) is a major impediment to credible analyses of the environmental effects of supersonic flight operations. Efforts to assess community response to high energy impulsive sounds are limited in at least two important ways. First, a paucity of appropriate empirical data makes it difficult to infer a dosage-response relationship by means similar to those used in the case of general transportation noise. Second, it is unclear how well the 'equal energy hypothesis' (the notion that duration, number, and level of individual events are directly interchangeable determinants of annoyance) applies to some forms of impulsive noise exposure. Some of the issues currently under consideration by a CHABA working group addressing these problems are discussed. These include means for applying information gained in controlled exposure studies about different rates of growth of annoyance with impulsive and non-impulsive sound exposure levels, and strategies for developing a dosage-response relationship in a data-poor area.

Fidell, Sanford↗
NASA NTRS1994

Main characteristics of the COMET/COMRADE experiments

Both the COMET (Collection en Orbite de Matiere Extra Terrestre) and the COMRADE (Collection of Micrometeorites, Residue and Debris Ejecta) programs are developed to the collection and analysis of the particles of various origins orbiting around the Earth at low altitudes (between approx. 300 and approx. 500 km). The COMET experiment is more specifically designed to be flown for a short period of time (a few days), in concordance with a meteor stream crossing the Earth. Thus, it results in a considerable enrichment in the collection of grains related to a given comet. The COMRADE experiment has been selected as a proposal for long-duration flights (a few months), in order to gain information on all sizes of particles present on low Earth orbits, including submicrometer grains. It has been accepted by ESA authorities for use on the EURECA 2 platform. The objectives of these studies are multiple. The use of passive detectors gives access to the chemical and isotopical properties of the grains in the micrometer size range, by analyzing either the particle remnant mixed with the target material, or the intact particle captured in a specific low-density material. The particle remnants of the micrometer-sized extraterrestrial grains, having impacted on purposely designed metallic collectors, are identified for complete and detailed chemical, isotopic, and organic analysis, thereby determining grain composition as well as the existence of organic and inorganic molecules, to be related with the possible cometary origin of the grains. Micrometer/submicrometer dust grains are also captured in a manner that ensures minimal particle degradation. The captured intact particles are returned to Earth for complete and detailed chemical, isotopic, spectral, mineralogical, and organic analysis.

Borg, J.↗
NASA NTRS1992

Stiffness and strength tailoring in uniform space-filling truss structures

This paper presents a deterministic procedure for tailoring the continuum stiffness and strength of uniform space-filling truss structures through the appropriate selection of truss geometry and member sizes (i.e., flexural and axial stiffnesses and length). The trusses considered herein are generated by replication of a characteristic truss cell uniformly through space. The repeating cells are categorized by one of a set of possible geometric symmetry groups derived using the techniques of crystallography. The elastic symmetry associated with each geometric symmetry group is identified to aid in the selection of an appropriate truss geometry for a given application. Stiffness and strength tailoring of a given truss geometry is enabled through explicit expressions relating the continuum stiffnesses and failure stresses of the truss to the stiffnesses and failure loads of its members. These expressions are derived using an existing equivalent continuum analysis technique and a newly developed analytical failure theory for trusses. Several examples are presented to illustrate the application of these techniques, and to demonstrate the usefulness of the information gained from this analysis.

Lake, Mark S.↗
NASA NTRS1995

Visualizing turbulent mixing of gases and particles

A physical model and interactive computer graphics techniques have been developed for the visualization of the basic physical process of stochastic dispersion and mixing from steady-state CFD calculations. The mixing of massless particles and inertial particles is visualized by transforming the vector field from a traditionally Eulerian reference frame into a Lagrangian reference frame. Groups of particles are traced through the vector field for the mean path as well as their statistical dispersion about the mean position by using added scalar information about the root mean square value of the vector field and its Lagrangian time scale. In this way, clouds of particles in a turbulent environment are traced, not just mean paths. In combustion simulations of many industrial processes, good mixing is required to achieve a sufficient degree of combustion efficiency. The ability to visualize this multiphase mixing can not only help identify poor mixing but also explain the mechanism for poor mixing. The information gained from the visualization can be used to improve the overall combustion efficiency in utility boilers or propulsion devices. We have used this technique to visualize steady-state simulations of the combustion performance in several furnace designs.

Ma, Kwan-Liu↗