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Viewing 1 to 21 of 21
2004-07-19
Technical Paper
2004-01-2322
S. A. Walker, J. Tweed, J. W. Wilson, R. K. Tripathi
The development of a Green’s function approach to ion transport greatly facilitates the modeling of laboratory radiation environments and allows for the direct testing of transport approximations of material transmission properties. Using this approach radiation investigators at the NASA Langley Research Center have established that simple solutions can be found for HZE ions by ignoring nuclear energy downshifts and dispersion. Such solutions were found to be supported by experimental evidence with HZE ion beams when multiple scattering was added. Lacking from the prior solutions were range and energy straggling and energy downshift and dispersion associated with nuclear events. In a more recent publication it was shown how these effects can be incorporated into the multiple fragmentation perturbation series. Analytical approximations for the first two perturbation terms were presented and the third term was evaluated numerically.
2006-07-17
Technical Paper
2006-01-2147
J. Tweed, S. A. Walker, J. W. Wilson, R. K. Tripathi, F. A. Cucinotta, F. F. Badavi
A new Green’s function code (GRNTRN) capable of simulating HZE ions with either laboratory or space boundary conditions is currently under development. The computational model consists of combinations of physical perturbation expansions based on the scales of atomic interaction, multiple scattering, and nuclear reactive processes with use of the Neumann-asymptotic expansions with non-perturbative corrections. The code contains energy loss due to straggling, nuclear attenuation, nuclear fragmentation with energy dispersion and downshifts. Recent publications have focused on code validation in the laboratory environment and have shown that the code predicts energy loss spectra accurately as measured by solid-state detectors in ion beam experiments. In this paper emphasis is placed on code validation with space boundary conditions.
2007-07-09
Technical Paper
2007-01-3118
J. Tweed, S. A. Walker, J. W. Wilson, R. K. Tripathi, F. F. Badavi, J. Miller, C. Zeitlin, L. H. Heilbronn
To meet the challenge of future deep space programs an accurate and efficient engineering code for analyzing the shielding requirements against high-energy galactic heavy radiations is needed. Such engineering design codes require establishing validation processes using laboratory ion beams and space flight measurements in realistic geometries. In consequence, a new version of the HZETRN code capable of simulating HZE ions with either laboratory or space boundary conditions is currently under development. The new code, GRNTRN, is based on a Green's function approach to the solution of Boltzmann's transport equation and like its predecessor is deterministic in nature. Code validation in the laboratory environment is addressed by showing that GRNTRN accurately predicts energy loss spectra as measured by solid-state detectors in ion beam experiments.
2007-07-09
Technical Paper
2007-01-3117
T. C. Slaba, J. H. Heinbockel, J. W. Wilson, S. R. Blattnig, M. S. Clowdsley, F. F. Badavi
In this paper we investigate three numerical techniques for solving the one-dimensional straight-ahead Boltzmann equation for calculating the flux of low energy neutrons produced within a shielding material. The one-dimensional Boltzmann equation is split into a forward and backward coupled system of equations representing the production of ions of various types within a shielding material. The three numerical methods are then compared with neutron data from the Mir and ISS space station as well as Monte Carlo simulations for the production of low energy neutrons.
2003-07-07
Technical Paper
2003-01-2330
J. Ware, J. Ferl, J. W. Wilson, M. S. Clowdsley, G. De Angelis, J. Tweed, C. J. Zeitlin, J. Miller, L. H. Heilbronn
Prior studies have been performed where basic fabric lay-ups of the current Shuttle spacesuit were tested for radiation shielding capabilities. It was found that the fabric portions of the suit give far less protection from radiation than previously estimated. This is due to the porosity and non-uniformity of the fabrics and LCVG components. These findings were incorporated into the spacesuit model developed at NASA Langley Research Center to estimate exposures for mission planning and evaluation of safety during radiation field disturbance. Overall material transmission properties were also less than optimal. In order to evaluate the radiation protection characteristics of some proposed new spacesuit materials, fifteen test target combinations of current baseline and new proposed spacesuit materials were exposed to a low-energy proton beam at Lawrence Berkeley National Laboratory. Each target combination contained all of the necessary spacesuit layers, i.e.
2003-07-07
Technical Paper
2003-01-2351
J. H. Heinbockel, G. A. Feldman, J. W. Wilson, R. C. Singleterry, M. S. Clowdsley
One goal of space radiation research is to reduce the computational time and increase the accuracy of various radiation calculations to aid in their use in a collaborative engineering environment. For example, a fast turn around time is a feature needed for comparison of radiation shielding effects associated with various design configurations of the International Space Station. Research toward this effort has been conducted on various forms of the low energy neutron Boltzmann equation. Simplified models involving the straight ahead approximation, which have fast computational speeds, have been developed at NASA Langley Research Center during the late 1980's as part of a larger high energy ion transport code. Various modifications to improve the accuracy of these computer codes have been an ongoing project. The goal to increase the accuracy of low energy neutron transport without effecting the fast computational times has been a successful ongoing research effort.
2001-07-09
Technical Paper
2001-01-2370
G. D. Qualls, J. W. Wilson, C. Sandridge, F. A. Cucinotta, J. E. Nealy, J. H. Heinbockel, C. P. Hugger, J. Verhage, B. M. Anderson, W. Atwell, N. Zapp, R. Barber
The projected radiation levels within the International Space Station (ISS) have been criticized by the Aerospace Safety Advisory Panel in their report to the NASA Administrator. Methods for optimal reconfiguration and augmentation of the ISS shielding are now being developed. The initial steps are to develop reconfigurable and realistic radiation shield models of the ISS modules, develop computational procedures for the highly anisotropic radiation environment, and implement parametric and organizational optimization procedures. The targets of the redesign process are the crew quarters where the astronauts sleep and determining the effects of ISS shadow shielding of an astronaut in a spacesuit. The ISS model as developed will be reconfigurable to follow the ISS. Swapping internal equipment rack assemblies via location mapping tables will be one option for shield optimization.
2001-07-09
Technical Paper
2001-01-2327
M. S. Clowdsley, J. W. Wilson, J. L. Shinn, F. F. Badavi, J. H. Heinbockel, W. Atwell
The long term exposure of astronauts on the developing International Space Station (ISS) requires an accurate knowledge of the internal exposure environment for human risk assessment and other onboard processes. The natural environment is moderated by the solar wind, which varies over the solar cycle. The HZETRN high charge and energy transport code developed at NASA Langley Research Center can be used to evaluate the neutron environment on ISS. A time dependent model for the ambient environment in low earth orbit is used. This model includes GCR radiation moderated by the Earth’s magnetic field, trapped protons, and a recently completed model of the albedo neutron environment formed through the interaction of galactic cosmic rays with the Earth’s atmosphere. Using this code, the neutron environments for space shuttle missions were calculated and comparisons were made to measurements by the Johnson Space Center with onboard detectors.
2002-07-15
Technical Paper
2002-01-2462
J. Ware, J. Ferl, J. W. Wilson, M. S. Clowdsley, G. de Angelis, J. Tweed, C. J. Zeitlin
In prior studies of the current Shuttle Spacesuit (SSA), where basic fabric lay-ups were tested for shielding capabilities, it was found that the fabric portions of the suit give far less protection than previously estimated due to porosity and non-uniformity of fabric and LCVG components. In addition, overall material transmission properties were less than optimum. A number of alternate approaches are being tested to provide more uniform coverage and to use more efficient materials. We will discuss in this paper, recent testing of new material lay-ups/configurations for possible use in future spacesuit designs.
2002-07-15
Technical Paper
2002-01-2460
M. S. Clowdsley, J. H. Hienbockel, F. F. Badavi, J. W. Wilson
Most of the neutrons seen in the habitable environment of spacecraft in LEO are produced in local materials of the spacecraft structures by the impact of the LEO radiation environment. There are two components of the neutron spectra: one produced near the forward direction and a diffuse isotropic component. The forward component satisfies a Volterra equation and is solved by standard marching procedures. The diffuse component is generally of lower energy and nearly isotropically scattered as they diffuse through the spacecraft structures. Leakage at near boundaries marks the diffusion process and solutions are strongly dependent on forward and backward boundaries with minor contributions from lateral diffusion along spacecraft wall structures. The diffuse neutron equation is solved using multigroup methods with impressed forward and backward boundary conditions.
2001-09-11
Technical Paper
2001-01-2938
Oscar R. González, W. Steven Gray, Arturo Tejada
Safety critical real-time computer systems such as digital fly-by-wire aircraft are designed to be highly reliable, able to detect and recover from faults, and fail in a safe state even in harsh environments. This paper presents an analytical tool that is being developed to enhance the design and verification of safety critical systems. The tool is used to analyze the effect of standard error recovery systems on closed-loop flight control systems. In particular, this paper develops models and analyzes the stability effect of error recovery rollback, reset, and restart systems in digital control systems due to system functional upsets induced by multiple burst waveforms (MBW’s) during a lightning flash. A simple example will be used to illustrate one use for the tool: comparison of different recovery methodologies by determining the minimum interarrival spacing between MBW’s to maintain closed-loop stability.
2008-06-29
Journal Article
2008-01-2162
T. C. Slaba, J. H. Heinbockel, S. R. Blattnig
Exposure estimates inside space vehicles, surface habitats, and high altitude aircraft exposed to space radiation are highly influenced by secondary neutron production. The deterministic transport code HZETRN has been identified as a reliable and efficient tool for such studies, but improvements to the underlying transport models and numerical methods are still necessary. In this paper, the forward-backward (FB) and directionally coupled forward-backward (DC) neutron transport models are derived, numerical methods for the FB model are reviewed, and a computationally efficient numerical solution is presented for the DC model. Both models are compared to the Monte Carlo codes HETC-HEDS and FLUKA, and the DC model is shown to agree closely with the Monte Carlo results.
2006-07-17
Technical Paper
2006-01-2149
T. C. Slaba, J. H. Heinbockel, J. W. Wilson, S. R. Blattnig, M. S. Clowdsley, F. F. Badavi
A new method is developed for calculating the low energy neutron flux in a space environment which is protected from galactic cosmic rays (GCR) and solar particle events (SPE) by shielding materials. Our calculations are compared with low energy neutron flux flight data recorded on four different STS low earth orbit missions. We also compare our neutron flux calculations with the low energy neutron flux data recorded by MIR. The low energy neutron flux calculations can be described as a deterministic method for solving the Boltzmann equation for the light ion flux associated with a given environment. Existing Monte Carlo neutron flux simulations associated with the MIR and ISS space stations are also compared with our deterministic method for calculating neutron flux.
2006-07-17
Technical Paper
2006-01-2148
S. A. Walker, J. Tweed, J. W. Wilson, R. K. Tripathi, F. A. Cucinotta
Recently, a new Green’s function code (GRNTRN) for simulation of HZE ion beams in the laboratory setting has been developed. Once fully developed and experimentally verified, GRNTRN will be a great asset in assessing radiation exposures in both the laboratory and space settings. The computational model consists of combinations of physical perturbation expansions based on the scales of atomic interaction, multiple elastic scattering, and nuclear reactive processes with use of Neumann-series expansions with non-perturbative corrections. The code contains energy loss with straggling, nuclear attenuation, nuclear fragmentation with energy dispersion and down shifts. Previous reports show that the new code accurately models the transport of ion beams through a single slab of material. Current research efforts are focused on enabling the code to handle multiple layers of material and the present paper reports on progress made towards that end.
2002-10-29
Technical Paper
2002-01-3179
Miroslav Joler, Christos Christodoulou, John Gaudet, Edl Schamiloglu, Karl Schoenbach, Ravinder Joshi, Mounir Laroussi
The evolution of high power microwave (HPM) sources into practical systems requires the development of compact pulsed power that can be integrated into mobile platforms. One approach to pursuing this objective, developed by researchers at Sandia National Laboratories (Sandia) [1], is to utilize parallel-stacked Blumlein transmission lines energized with a compact Marx generator. Such a configuration would be capable of driving low impedance HPM sources with a long pulse waveform. One of the limitations of this approach is field enhancement-induced breakdown at the edges of the line. Another limitation is percolation of, and subsequent breakdown of the liquid dielectric that is used in the system. This paper describes a research program that, both computationally and experimentally, is studying electrical breakdown in such transmission line configurations for a variety of dielectric materials and substrate geometries.
2002-07-15
Technical Paper
2002-01-2332
R. K. Tripathi, L. C. Simonsen, J. E. Nealy, P. A. Troutman, J. W. Wilson
The great cost of added radiation shielding is a potential limiting factor in many deep space missions. For this enabling technology, we are developing tools for optimized shield design over multi-segmented missions involving multiple work and living areas in the transport and duty phase of various space missions. The total shield mass over all pieces of equipment and habitats is optimized subject to career dose and dose rate constraints. Preliminary studies of deep space missions indicate that for long duration space missions, improved shield materials will be required. The details of this new method and its impact on space missions and other technologies will be discussed. This study will provide a vital tool for evaluating Gateway designs in their usage context. Providing protection against the hazards of space radiation is one of the challenges to the Gateway infrastructure designs.
2003-07-07
Technical Paper
2003-01-2331
J. Tweed, J. W. Wilson, R. K. Tripathi, J. Miller, C. Zeitlin, L. H. Heilbronn, S. Walker
As shielding materials are developed for protection against the hazards of galactic cosmic rays, it is desirable to develop a protocol for rapid assessment of shielding properties. Solid state energy loss detectors are often used to estimate the charge and energy of particles in ion beam experiments. The direct measurement is energy deposited in the detector. As a means of separating the charge components in typical shield transmission studies with observation, a stack of many such detectors is used. With high-energy beams and thin targets, surviving primaries and fragments emerging from the target have nearly-equal velocities and deposited energy scales with the square of the charge, simplifying the data analysis. The development of a transport model for the shield and detector arrangement and evaluation of prediction of the energy loss spectrum for direct comparison with the experimentally derived data allows a rapid assessment of the shield transmission characteristics.
2002-04-16
Technical Paper
2002-01-1545
Yesim Sireli, Paul Kauffmann
One area of NASA's Aviation Safety Program involves investigation of the feasibility of advanced Aviation Weather Information Systems to reduce accident rates. An element of this program involves integrating weather information systems into the general aviation cockpit. Since the automotive and trucking industry currently use Intelligent Transportation Systems (ITS), this study investigated the possibility of applying similar systems in the cockpit of general aviation aircraft and examined three areas that support better understanding of this possibility. The first includes market activities in general ITS products. The second area involves a market research survey, to identify the user requirements for new in-cockpit information systems. The third area examines the historical growth patterns of GPS systems to estimate possible market acceptance of future information systems that have parallels with ITS in general aviation.
1996-07-01
Technical Paper
961598
Zhong Shi, Dongchuan Wu, Robert L. Ash
Experiments have been conducted to determine the effectiveness of using an RF glow-discharge to increase oxygen yield from Mars atmosphere at moderate operating temperatures. Based on the tests reported here, an RF glow-discharge requires significantly less electrical power than a DC glow-discharge, while operating at lower temperatures. A brief discussion of how this approach can be combined with in situ resource utilization (ISRU) systems employing stabilized Zirconia membranes has also been presented.
2006-07-17
Technical Paper
2006-01-2103
William Atwell, John Nealy, Martha Clowdsley
The development of “next generation” human-rated space vehicles, surface habitats and rovers, and spacesuits will require the integration of low-cost, lightweight materials that also include excellent mechanical, structural, and thermal properties. In addition, it is highly desirable that these materials exhibit excellent space radiation exposure mitigation properties for protection of both the crew and onboard sensitive electronics systems. In this paper, we present trapped electron and proton space radiation exposure computational results for a variety of materials and shielding thicknesses for several earth orbit scenarios that include 1) low earth orbit (LEO), 2) medium earth orbit (MEO), and 3) geostationary orbit (GEO). We also present space radiation exposure (galactic cosmic radiation and solar particle event) results as a function of selected materials and thicknesses.
2004-07-19
Technical Paper
2004-01-2327
Brooke M. Anderson, John W. Wilson, John E. Nealy, Francis F. Badavi, John Aiello
The effects of both the cosmic ray heavy ion exposures and the intense trapped electron exposures are examined with respect to impact on cellular system survival on exterior spacecraft surfaces as well as at interior (shielded) locations for a sample mission to Jupiter’s moons. Radiation transport through shield materials and subsequent exposures are calculated with the established Langley heavy ion and electron deterministic codes. In addition to assessing fractional DNA single and double strand breaks, a variety of cell types are examined that have greatly differing radio-sensitivities. Finally, implications as to shield requirements for controlled biological experiments are discussed.
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