Tectonic and geologic evolution of the Espanola basin, Rio Grande rift - Structure, rate of extension, and relation to the state of stress in the western United States
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Golombek, M. P.↗
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New fine structure cooling rate
One of the dominant electron cooling processes in the ionosphere is caused by electron impact induced fine structure transitions among the ground state levels of atomic oxygen. This fine structure cooling rate is based on theoretical cross sections. Recent advances in the numerical cross section determinations to include polarization effects and more accurate representations of the atomic target result in new lower values. These cross sections are employed in this paper to derive a new fine structure cooling rate which is between 40% and 60% of the currently used rate. A new generalized formula is presented for the cooling rate (from which the fine structure cooling rate is derived), valid for arbitrary mass and temperature difference of the colliding particles and arbitrary inelastic energy difference.
Hoegy, W. R.↗
New fine structure cooling rate
One of the dominant electron cooling processes in the ionosphere is caused by electron impact induced fine structure transitions among the ground state levels of atomic oxygen. This fine structure cooling rate is based on theoretical cross sections. Recent advances in the numerical cross section determinations to include polarization effects and more accurate representations of the atomic target result in new lower values. These cross sections are employed in this paper to derive a new fine structure cooling rate which is between 40% and 60% of the currently used rate. A new generalized formula is presented for the cooling rate (from which the fine structure cooling rate is derived), valid for arbitrary mass and temperature difference of the colliding particles and arbitrary inelastic energy difference.
Hoegy, W. R.↗
Structural Certification of Human-Rated Inflatable Space Structures
This paper details the results of an initial study to develop a certification plan for human-rated inflatable space structures, including guidelines for qualification testing. Habitable softgoods inflatables are multi-layered shell structures that use high-strength webbing, cordage and broadcloth fabric to carry the skin loads of a variety of volumetric shapes and structural architectures. The primary objectives of this study are to define the key parameters that affect these structures and propose a statistically robust approach to defining safety and knockdown factors based on test and analysis. Current NASA standards for habitable inflatable space structures use a factor of safety of 4, which was inherited from airship design criteria. An updated approach to defining a design factor, taking into account material strength variability, load variability in the article, number of test samples, and damage and degradation effects is specified. Accurate analytical modeling of these structures is hindered by the difficulty of obtaining accurate and consistent material data due to load-history- dependent, nonlinear load versus strain behavior. A building block approach to certification is detailed that uses stochastic modeling and statistical test design and analysis to address the unique challenges these high-strength softgoods structures present. Human-rated inflatable modules are a transformative capability for launching much larger habitable volumes into space than is possible with rigid shell structures. This research aims to provide the framework for certifying these structures for future human space exploration missions.
Jones, Thomas C.↗
Turbulence structure at high shear rate
The structure of homogeneous turbulence in the presence of a high shear rate is studied using results obtained from three-dimensional time-dependent numerical simulations of the Navier-Stokes equations on a grid of 512 x 128 x 128 node points. It is shown that high shear rate enhances the streamwise fluctuating motion to such an extent that a highly anisotropic turbulence state with a one-dimensional velocity field and two-dimensional small-scale turbulence develops asymptotically as total shear increases. Instantaneous velocity fields show that high shear rate in homogeneous turbulent shear flow produces structures which are similar to the streaks present in the viscous sublayer of turbulent boundary layers.
Lee, Moon Joo↗
Experimental correlation of melt structures, nucleation rates, and thermal histories of silicate melts
The theory and measurement of the structure of liquids is an important aspect of modern metallurgy and igneous petrology. Liquid structure exerts strong controls on both the types of crystals that may precipitate from melts and on the chemical composition of those crystals. An interesting aspect of melt structure studies is the problem of melt memories; that is, a melt can retain a memory of previous thermal history. This memory can influence both nucleation behavior and crystal composition. This melt memory may be characterized quantitatively with techniques such as Raman, infrared and NMR spectroscopy to provide information on short-range structure. Melt structure studies at high temperature will take advantage of the microgravity conditions of the Space Station to perform containerless experiments. Melt structure determinations at high temperature (experiments that are greatly facilitated by containerless technology) will provide invaluable information for materials science, glass technology, and geochemistry. In conjunction with studies of nucleation behavior and nucleation rates, information relevant to nucleation in magma chambers in terrestrial planets will be acquired.
Boynton, W. V.↗
Reliability and risk assessment of structures
Development of reliability and risk assessment of structural components and structures is a major activity at Lewis Research Center. It consists of five program elements: (1) probabilistic loads; (2) probabilistic finite element analysis; (3) probabilistic material behavior; (4) assessment of reliability and risk; and (5) probabilistic structural performance evaluation. Recent progress includes: (1) the evaluation of the various uncertainties in terms of cumulative distribution functions for various structural response variables based on known or assumed uncertainties in primitive structural variables; (2) evaluation of the failure probability; (3) reliability and risk-cost assessment; and (4) an outline of an emerging approach for eventual certification of man-rated structures by computational methods. Collectively, the results demonstrate that the structural durability/reliability of man-rated structural components and structures can be effectively evaluated by using formal probabilistic methods.
Chamis, C. C.↗
Plasma environment effects on K lines of astrophysical interest I. Atomic structure, radiative rates, and Auger widths of oxygen ions
Aims. In the context of black-hole accretion disks, the main goal of the present study is to estimate the plasma environment effects on the atomic structure and radiative parameters associated with the K-vacancy states in ions of the oxygen isonuclear sequence. Methods. We used a time-averaged Debye–Hückel potential for both the electron–nucleus and the electron–electron interactions implemented in the fully relativistic multiconfiguration Dirac–Fock (MCDF) method. Results. Modified ionization potentials, K thresholds, Auger widths, and radiative transition wavelengths and rates are reported for O I–O VII in plasma environments with electron temperature and density ranges 10(exp 5)−10(exp 7) K and 10(exp 18)−10(exp 22)/cu.cm.
J. Deprince↗
Simulation and evaluation of latent heat thermal energy storage
The relative value of thermal energy storage (TES) for heat pump storage (heating and cooling) as a function of storage temperature, mode of storage (hotside or coldside), geographic locations, and utility time of use rate structures were derived. Computer models used to simulate the performance of a number of TES/heat pump configurations are described. The models are based on existing performance data of heat pump components, available building thermal load computational procedures, and generalized TES subsystem design. Life cycle costs computed for each site, configuration, and rate structure are discussed.
Sigmon, T. W.↗
Deflagration rate, surface structure, and subsurface profile of self-deflagrating single crystals of ammonium perchlorate
Pure ammonium perchlorate single crystal self deflagration, determining energy transfer mechanisms from pressure effects, combustion characteristics and subsurface profile
Boggs, T. L.↗
On the structure of rate 1/n convolutional codes.
It is shown what choice there is in assigning output digits to transitions of binary rate 1/n code trellis so that the latter will correspond to a convolutional code. A new upper bound on free distance of rate 1/n convolutional codes is also derived, and the results obtained are used to determine the length of the largest input sequence that can conceivably result in an output whose weight is equal to the free distance of a code of rate 1/2.
Bahl, L.↗
Explorer satellite measurements of meteoroid penetration rates in structural materials
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Oneal, R. L.↗
Additive Manufactured Human-rated Spacecraft Structures: Certification Challenges
This presentation describes additive manufacturing work ongoing at NASA and discusses certification challenges with a focus on fracture control.
Mcelroy, Mark W.↗
Structure of turbulence at high shear rate
The structure of homogeneous turbulence subject to high shear rate has been investigated by using three-dimensional, time-dependent numerical simulations of the Navier-Stokes equations. This study indicates that high shear rate alone is sufficient for generation of the streaky structures, and that the presence of a solid boundary is not necessary. Evolution of the statistical correlations is examined to determine the effect of high shear rate on the development of anisotropy in turbulence. It is shown that the streamwise fluctuating motions are enhanced so profoundly that a highly anisotropic turbulence state with a 'one-component' velocity field and 'two-component' vorticity field develops asymptotically as total shear increases. Because of high-shear rate, rapid distortion theory predicts remarkably well the anisotropic behavior of the structural quantities.
Lee, Moon Joo↗
Wire Insulation Flammability Experiment: USML-1 One Year Post Mission Summary
Herein we report the results from the Wire Insulation Flammability (WIF) Experiment performed in the Glovebox Facility on the USML-1 mission. This experiment explored various aspects of electrically induced fire scenarios in a reduced gravity environment. Under quiescent microgravity conditions, heat and mass transfer are dominated by diffusive and radiative transport; while in normal-gravity buoyancy induced convection often dominates. Of considerable scientific and practical interest is the intermediate situation of combustion occurring in the presence of imposed gas flows, with lower characteristic velocities than those induced by buoyancy in noma1 gravity. Two distinct cases naturally arise: flow direction opposed to, or concurrent with, the flame spread direction. Two tests of each kind were conducted in the WIF experiment, providing the first controlled demonstration of flame spreading in forced convection ever conducted in space. Four test modules were flown. The wire insulation, 1.5 mm in diameter, was polyethylene, extruded onto nichrome wire. Temperatures of the wh3 cores and insulation heated in quiescent and flowing environments were measured. Video and still-camera images of the samples, burning in air flowing at approximately 10 cm/sec, were recorded to obtain flame characteristics including spread rate, structure and temperature. Flame spread rates in concurrent flow were approximately twice those in opposed flow. In concurrent and opposed flow regimes, the spreading flames stabilized around a bead of molten insulation material, within which bubble nucleation was observed. An ignition attempt without flow mated a quiescent cloud of vaporized fuel which ignited dramatically yet failed to sustain normal flame spread. Finally, all tests produced substantial soot agglomerates, particularly the concurrent flow tests; and the collected soot has a morphology very distinct from soot formed in normal gravity flames. Several unexpected and unique microgravity combustion phenomena were observed.
Greenberg, Paul S.↗
The effect of composition and cooling rate on the structure of rapidly solidified (Fe, Ni)3Al-C alloy
The quench rate-metastable structure dependence in the Fe-20Ni-8Al-2C wt pct alloy has been experimentally studied. The nonequilibrium gamma-prime and gamma phases were noted in foils 65-100 microns thick, while at higher quench rates (thinner samples) the matrix was found to be in a disordered fcc gamma phase with kappa carbide precipitates. With the addition of silicon to the alloys, the nonequilibrium gamma-prime and gamma structures are observed at higher cooling rates.
Myers, S. A.↗
Inflatable Habitats Technology Development
For many years inflatable structures have been theorized for use as satellite dishes, deployable arrays and human habitats. They fall into human-rated and non-human rated structures. As such the structural design requirements and safety redundancy are much different. This paper will discuss the Habitat and Surface Construction Technology that would support the development of Mars greenhouses as well as habitats. This paper will briefly describe the ISS TransHab architectural design and structural testing for the proposed as a habitation module for the International Space Station. It will also discuss inflatable greenhouse design considerations and examples.
Kennedy, Kriss J.↗
Greenhouse models of Venus' high surface temperature, as constrained by Pioneer Venus measurements
Recent measurements conducted from the Pioneer Venus probes and orbiter have provided a significantly improved definition of the solar net flux profile, the gaseous composition, temperature structure, and cloud properties of Venus' lower atmosphere. Using these data, we have carried out a series of one-dimensional radiative-convective equilibrium calculations to determine the viability of the greenhouse model of Venus' high surface temperature and to assess the chief contributors to the greenhouse effect. New sources of infrared opacity include the permitted transitions of SO2, CO, and HCl as well as opacity due to several pressure-induced transitions of CO2. We find that the observed surface temperature and lapse rate structure of the lower atmosphere can be reproduced quite closely with a greenhouse model that contains the water vapor abundance reported by the Venera spectrophotometer experiment. Thus the greenhouse effect can account for essentially all of Venus' high surface temperature. The prime sources of infrared opacity are, in order of importance, CO2, H2O, cloud particles, and SO2, with CO and HCl playing very minor roles.
Pollack, J. B.↗