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Technical Paper

Steps Toward Developing a Multi-layer Green’s Function Code for Ion Beam Transport

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.
Technical Paper

An Improved Green’s Function Code for HZE Ion Transport

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.
Technical Paper

Some New Results in the Green’s Function Method for Ion Beam Transport

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.
Technical Paper

Test Results of Improved Spacesuit Shielding Components

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.
Technical Paper

Study of High Energy Storage Blumlein Transmission Lines as High Power Microwave Drivers

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.
Technical Paper

Shield Optimization in Simple Geometry for the Gateway Concept

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.
Technical Paper

Analytical Tools for the Design and Verification of Safety Critical Control Systems

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.
Technical Paper

Neutron Environment Calculations for Low Earth Orbit

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.
Technical Paper

International Space Station Radiation Shielding Model Development

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.
Technical Paper

An Investigation of Radio Frequency Enhanced Glow Discharge Production of Oxygen from Carbon Dioxide

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.