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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Atomic-Oxygen-Durable Microsheet Glass Reflector

Advanced solar dynamic concentrator concepts being considered by the NASA Lewis Research Center for space power systems include one utilizing microsheet glass coated with silver. For this material, a 5000-angstrom layer of silver is deposited on the back side of a contoured piece of microsheet glass, 0.2-mm thick. The silvered side is then bonded to a contoured aluminum, magnesium, or graphite epoxy face sheet with a space-qualified, pressure-sensitive thin-film adhesive. Experience gained from the development of this technology suggests that this material may reduce the cost and improve the performance of solar dynamic concentrators. This microsheet glass technology provides an effective barrier to atomic oxygen attack and provides the opportunity to utilize silver-reflective coatings in low-Earth-orbit solar dynamic applications.

Source record↗
NASA NTRS2007

Dynamics of Nanoscale Grain-Boundary Decohesion in Aluminum by Molecular-Dynamics Simulation

The dynamics and energetics of intergranular crack growth along a flat grain boundary in aluminum is studied by a molecular-dynamics simulation model for crack propagation under steady-state conditions. Using the ability of the molecular-dynamics simulation to identify atoms involved in different atomistic mechanisms, it was possible to identify the energy contribution of different processes taking place during crack growth. The energy contributions were divided as: elastic energy, defined as the potential energy of the atoms in fcc crystallographic state; and plastically stored energy, the energy of stacking faults and twin boundaries; grain-boundary and surface energy. In addition, monitoring the amount of heat exchange with the molecular-dynamics thermostat gives the energy dissipated as heat in the system. The energetic analysis indicates that the majority of energy in a fast growing crack is dissipated as heat. This dissipation increases linearly at low speed, and faster than linear at speeds approaching 1/3 the Rayleigh wave speed when the crack tip becomes dynamically unstable producing periodic dislocation bursts until the crack is blunted.

Yamakov, V.↗
NASA NTRS1987

The survivability of large space-borne reflectors under atomic oxygen and micrometeoroid impact

Solar dynamic power system mirrors for use on space station and other spacecraft flown in low Earth orbit (LEO) are exposed to the harshness of the LEO environment. Both atomic oxygen and micrometeoroids/space debris can degrade the performance of such mirrors. Protective coatings will be required to protect oxidizable reflecting media, such as silver and aluminum, from atomic oxygen attack. Several protective coating materials have been identified as good candidates for use in this application. The durability of these coating/mirror systems after pinhole defects have been inflicted during their fabrication and deployment or through micrometeoroid/space debris impact once on-orbit is of concern. Studies of the effect of an oxygen plasma environment on protected mirror surfaces with intentionally induced pinhole defects have been conducted at NASA Lewis and are reviewed. It has been found that oxidation of the reflective layer and/or the substrate in areas adjacent to a pinhole defect, but not directly exposed by the pinhole, can occur.

Gulino, D. A.↗
NASA NTRS1987

The survivability of large space-borne reflectors under atomic oxygen and micrometeoroid impact

Solar dynamic power system mirrors for use on Space Station and other spacecraft flown in low earth orbit (LEO) are exposed to the harshness of the LEO environment. Both atomic oxygen and micrometeoroids/space debris can degrade the performance of such mirrors. Protective coatings will be required to protect oxidizable reflecting media, such as silver and aluminum, from atomic oxygen attack. Several protective coating materials have been identified as good candidates for use in this application. The durability of these coating/mirror systems after pinhole defects have been inflicted during their fabrication and deployment or through micrometeoroid/space debris impact once on-orbit is of concern. Studies of the effect of an oxygen plasma environment on protected mirror surfaces with intentionally induced pinhole defects have been conducted at NASA Lewis and are reviewed. It has been found that oxidation of the reflective layer and/or the substrate in areas adjacent to a pinhole defect, but not directly exposed by the pinhole, can occur.

Gulino, Daniel A.↗
NASA NTRS2022

Building and Breaking Carbon Composites with REACTER

Carbon-based composites have become indispensable materials in aerospace and other high-performance applications, yet obtaining a detailed, nanoscale understanding of their morphology and failure mechanisms using only experimental methods remains a difficult challenge. REACTER is a versatile computational modeling tool for atomistic molecular dynamics simulations designed to model chemical reactions at the speed and length scales of classical force fields. In this work, several recent features of REACTER were applied to the creation and subsequent mechanical testing of two classes of carbon composites: carbon nanotube (CNT) composites and carbon fiber reinforced polymers (CFRP). A network of CNTs was grown dynamically using the new ‘create atoms’ feature of REACTER. The CNT filler was embedded into a polyarylacetylene (PAA) matrix by simulated in situ polymerization to obtain the final composite model. To generate the second class of carbon composite, fully carbonized (graphitic) carbon fiber morphologies were created by the method of Desai et al. [1], but using the advanced reaction constraints framework of REACTER. Two fiber models were created, representing a circular carbon fiber core and a flat surface, and similarly infiltrated with resin to obtain the final CFRP structure. Failure mechanisms were elucidated by simulating mechanically induced bond breaking, as characterized by third order DFT-based tight-binding simulations, via a reaction constraint on the total potential energy of the involved atoms.

Polymer↗
NASA NTRS1995

Theoretical overview and modeling of the sodium and potassium atmospheres of the moon

A general theoretical overview for the sources, sinks, gas-surface interactions, and transport dynamics of sodium and potassium in the exospheric atmosphere of the Moon is given. These four factors, which control the spatial distribution of these two alkali-group gases about the Moon, are incorporated in numerical models. The spatial nature and relative importance of the initial source atoms atmosphere (which must be nonthermal to explain observational data) and the ambient (ballistic hopping) atom atmosphere are examined. The transport dynamics, atmospheric structure, and lunar escape of the nonthermal source atoms are time variable with season of the year and lunar phase because of their dependence on the radiation acceleration experienced by sodium and potassium atoms as they resonantly scatter solar photons. The dynamic transport time of fully thermally accomodated ambient atoms along the surface because of solar radiation acceleration (only several percent of surface gravity) is larger than the photoionization lifetimes and hence unimportant in determining the local density, although for potassium the situation is borderline. The sodium model was applied to analyze sodium observations of the sunward brightness profiles acquired near last quarter by Potter & Morgan (1988b) extending from the surface to an altitude of 1200 km, and near first quarter by Mendillo, Baumgardner, & Flynn (1991), extending in altitude from approximately 1430 to approximately 7000 km. The observations at larger altitudes could be fitted only for source atoms having a velocity distribution with a tail that is mildly nonthermal (like an approximately 1000 K Maxwell-Boltzmann distribution). Solar wind sputtering appears to a be a viable source atom mechanism for the sodium observations with photon-simulated desorption also possible but highly uncertain, although micrometeoroid impact vaporization appears to have a source that is too small and too hot, with likely an incorrect angular distribution about the Moon.

Smyth, William H.↗
NASA NTRS1969

Energy and chemical reaction. I

Reagent translational energy effect on dynamics of ionic and atomic reactions, using nuclear recoil and chemical accelerator methods

Wolfgang, R.↗
NASA NTRS1972

Use of LEED, Auger emission spectroscopy and field ion microscopy in microstructural studies.

The studies reported were conducted to gain a fundamental understanding of adhesion and dynamic friction on an atomic or microscopic level. Fundamental aspects of low energy electron diffraction (LEED), Auger emission spectroscopy (AES), and field ion microscopy (FIM) are discussed. Typical results of studies conducted are considered, giving attention to LEED-AES experiments, pin and disk experiments, and field ion microscope investigations.

Ferrante, J.↗
NASA NTRS1987

Implementation of variable time step stochastic dynamics for electronically inelastic gas-surface collisions

A variable time step algorithm has been implemented for solving the stochastic equations of motion for gas-surface collisions. It has been tested for a simple model of electronically inelastic collisions with an insulator surface in which the phonon manifold acts as a heat bath and electronic states are localized. In addition to reproducing the accurate nuclear dynamics of the surface atoms, numerical calculations have shown the algorithm to yield accurate ensemble averages of physical observables such as electronic transition probabilities and total energy loss of the gas atom to the surface. This new algorithm offers a gain in efficieny of up to an order of magnitude compared to fixed time step integration.

Garrett, Bruce C.↗
NASA NTRS1987

Atomic hydrogen production rates for comet P/Halley from observations with Dynamics Explorer I

Newly analyzed observations of the Dynamics Explorer I (DE1), launched on August 3, 1981, were used to determine the hydrogen production rate for Comet Halley at heliocentric distances, r, less than about 1.5 AU from measurements of the total Lyman-alpha flux at earth due to the cometary neutral hydrogen distribution. The production rates, determined as a function of r, were found to be consistent with in situ measurements from the Giotto and Vega spacecraft. The calculated rates are also consistent with remote observations using two sounding rockets and with the Pioneer-Venus and IUE spacecraft.

Craven, J. D.↗
NASA NTRS1994

Eighteenth Space Simulation Conference: Space Mission Success Through Testing

The Institute of Environmental Sciences' Eighteenth Space Simulation Conference, 'Space Mission Success Through Testing' provided participants with a forum to acquire and exchange information on the state-of-the-art in space simulation, test technology, atomic oxygen, program/system testing, dynamics testing, contamination, and materials. The papers presented at this conference and the resulting discussions carried out the conference theme 'Space Mission Success Through Testing.'

Stecher, Joseph L., III↗
NASA NTRS1994

A thermosphere-ionosphere-mesosphere-electrodynamic general circulation model (time-GCM): Equinox solar cycle minimum simulations (30-500 km)

A new simulation model of the mesosphere, thermosphere, and ionosphere with coupled electrodynamics has been developed and used to calculate the global circulation, temperature and compositional structure between 30-500 km for equinox, solar cycle minimum, geomagnetic quiet conditions. The model incorporates all of the features of the National Center for Atmospheric Research (NCAR) thermosphere-ionosphere- electrodynamics general circulation model (TIE-GCM) but the lower boundary has been extended downward from 97 to 30 km (10 mb) and it includes the physical and chemical processes appropriate for the mesosphere and upper stratosphere. The first simulation used Rayleigh friction to represent gravity wave drag in the middle atmosphere and although it was able to close the mesospheric jets it severely damped the diurnal tide. Reduced Rayleigh friction allowed the tide to penetrate to thermospheric heights but did not close the jets. A gravity wave parameterization developed by Fritts and Lu (1993) allows both features to exist simultaneously with the structure of tides and mean flow dependent upon the strength of the gravity wave source. The model calculates a changing dynamic structure with the mean flow and diurnal tide dominant in the mesosphere, the in-situ generated semi-diurnal tide dominating the lower thermosphere and an in-situ generated diurnal tide in the upper thermosphere. The results also show considerable interaction between dynamics and composition, especially atomic oxygen between 85 and 120 km.

Roble, R. G.↗
NASA NTRS1995

Modelling of the outer heliosphere

The interaction of the outflowing solar wind with the local interstellar medium (LISM) is complicated by many factors--the solar wind itself is a highly dynamical medium, interstellar neutral atoms can interact with the heliospheric boundaries in a complex fashion and the solar wind can be decelerated via mass-loading associated with pick-up ions, for example. Anomalous and galactic cosmic rays besides being modulated by the solar wind, may react back on the heliospheric boundaries leading to possibly significant structural modifications. These and other factors suggest that the physics of the outer heliosphere is strongly influenced by the properties of the very LISM and is quite different from the physics of the inner heliosphere. In this talk, we will try to synthesize the many recent developments in modelling the outer heliosphere and boundaries, encompassing both local and global models. Special emphasis will be placed on identifying those aspects of the various models which have observational implications.

Zank, G. P.↗
NASA NTRS1998

20th Space Simulation Conference: The Changing Testing Paradigm

The Institute of Environmental Sciences' Twentieth Space Simulation Conference, "The Changing Testing Paradigm" provided participants with a forum to acquire and exchange information on the state-of-the-art in space simulation, test technology, atomic oxygen, program/system testing, dynamics testing, contamination, and materials. The papers presented at this conference and the resulting discussions carried out the conference theme "The Changing Testing Paradigm."

Stecher, Joseph L., III↗
NASA NTRS1999

20th Space Simulation Conference: The Changing Testing Paradigm

The Institute of Environmental Sciences and Technology's Twentieth Space Simulation Conference, "The Changing Testing Paradigm" provided participants with a forum to acquire and exchange information on the state-of-the-art in space simulation, test technology, atomic oxygen, program/system testing, dynamics testing, contamination, and materials. The papers presented at this conference and the resulting discussions carried out the conference theme "The Changing Testing Paradigm."

Stecher, Joseph L., III↗
NASA NTRS2000

21st Space Simulation Conference: The Future of Space Simulation Testing in the 21st Century

The Institute of Environmental Sciences and Technology's Twenty-first Space Simulation Conference, "The Future of Space Testing in the 21st Century" provided participants with a forum to acquire and exchange information on the state-of-the-art in space simulation, test technology, atomic oxygen, programs/system testing, dynamics testing, contamination, and materials. The papers presented at this conference and the resulting discussions carried out the conference theme "The Future of Space Testing in the 21st Century."

Stecher, Joseph L., III↗
NASA NTRS1999

Monte Carlo Simulation of Alloy Design Techniques: Fracture and Welding Studied Using the BFS Method for Alloys

Large-scale simulations of dynamic processes at the atomic level have developed into one of the main areas of work in computational materials science. Until recently, severe computational restrictions, as well as the lack of accurate methods for calculating the energetics, resulted in slower growth in the area than that required by current alloy design programs. The Computational Materials Group at the NASA Lewis Research Center is devoted to the development of powerful, accurate, economical tools to aid in alloy design. These include the BFS (Bozzolo, Ferrante, and Smith) method for alloys (ref. 1) and the development of dedicated software for large-scale simulations based on Monte Carlo- Metropolis numerical techniques, as well as state-of-the-art visualization methods. Our previous effort linking theoretical and computational modeling resulted in the successful prediction of the microstructure of a five-element intermetallic alloy, in excellent agreement with experimental results (refs. 2 and 3). This effort also produced a complete description of the role of alloying additions in intermetallic binary, ternary, and higher order alloys (ref. 4).

Bozzolo, Guillermo H.↗
NASA NTRS2015

Dynamics of the Vacuum and Casimir Analogs to the Hydrogen Atom

This paper will discuss the current viewpoint of the vacuum state and explore the idea of a "natural" vacuum as opposed to immutable, non-degradable vacuum. This concept will be explored for all primary quantum numbers to show consistency with observation at the level of Bohr theory. A comparison with the Casimir force per unit area will be made, and an explicit function for the spatial variation of the vacuum density around the atomic nucleus will be derived. This explicit function will be numerically modeled using the industry multi-physics tool, COMSOL(trademark), and the eigenfrequencies for the n = 1 to n = 7 states will be found and compared to expectation.

White, Harold↗