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Analysis of impacts on fused silica was motivated by the design of the mirror for the James Webb Space Telescope (JWST). The JWST is expected to have a large-diameter mirror shaded from sunlight but open to space. One of the candidate mirror materials is fused silica; the other candidate materials are ultra-low expansion (ULE) glass and O-30 beryllium. Historically, most meteoroid tests have concerned themselves with the degraded strength of the substrate; JWST is primarily concerned with maintaining its precise optical figure. Micrometeoroids can have velocities of 50 km/s or higher. Although the velocity in the analysis did not exceed 10 km/s, the computer model included a fit to shock Hugoniot data for fused silica with pressures as high as 700 GPa, typical of impacts at velocities higher than 10 km/s. The computer model also included the first-order phase transformation observed in fused silica. The calculations were made with the AUTODYN hydrocode [1], which includes smooth particle hydrodynamic (SPH) and Lagrange solvers with other modules and features for coupling them together. For the analysis of impact, both SPH and Lagrange methods were used. Using the static relaxation option, the analysis continued from crater formation to a late-time static solution from which the effect of the impact on the optics could be determined. Both low and high energy impacts were computed using the fused silica model. For the low energy impact, the computed crater depth, crater diameter, and spall diameter closely matched both historical data for fused silica and values measured by Auburn University/ Hypervelocity Impact Facility (AU/HIF) for two typical fused silica sites and one ULE site. For the high energy impact, the computed values matched historical data for fused silica but not the data measured by AU/HIF for three typical ULE sites. The discrepancy can be explained by the difference in the response of fused silica and ULE under impact, as seen in historical trends and as observed by AU/HIF. Optical interferometry of the surfaces of one of the mirrors revealed deformation in the vicinity of particle impacts that matched that estimated with a static model, and the deformation was consistent with that computed by AUTODYN.

NASA's Advanced Exploration Systems (AES) program is developing prototype systems, demonstrating key capabilities, and validating operational concepts for future human missions beyond Earth orbit. These forays beyond the confines of earth's gravity will place unprecedented demands on launch systems. They must launch the supplies needed to sustain a crew over longer periods for exploration missions beyond earth's moon. Thus all spacecraft systems, including those for the separation of metabolic carbon dioxide and water from a crewed vehicle, must be minimized with respect to mass, power, and volume. Emphasis is also placed on system robustness both to minimize replacement parts and ensure crew safety when a quick return to earth is not possible. Current efforts are focused on improving the current state-of-the-art systems utilizing fixed beds of sorbent pellets by evaluating structured sorbents, seeking more robust pelletized sorbents, and examining alternate bed configurations to improve system efficiency and reliability. These development efforts combine testing of sub-scale systems and multi-physics computer simulations to evaluate candidate approaches, select the best performing options, and optimize the configuration of the selected approach. This paper describes the continuing development of atmosphere revitalization models and simulations in support of the Atmosphere Revitalization Recovery and Environmental Monitoring (ARREM) project within the AES program.

"NASA's Advanced Exploration Systems (AES) program is pioneering new approaches for rapidly developing prototype systems, demonstrating key capabilities, and validating operational concepts for future human missions beyond Earth orbit" (NASA 2012). These forays beyond the confines of earth's gravity will place unprecedented demands on launch systems. They must not only blast out of earth's gravity well as during the Apollo moon missions, but also launch the supplies needed to sustain a crew over longer periods for exploration missions beyond earth's moon. Thus all spacecraft systems, including those for the separation of metabolic carbon dioxide and water from a crewed vehicle, must be minimized with respect to mass, power, and volume. Emphasis is also placed on system robustness both to minimize replacement parts and ensure crew safety when a quick return to earth is not possible. Current efforts are focused on improving the current state-of-the-art systems utilizing fixed beds of sorbent pellets by evaluating structured sorbents, seeking more robust pelletized sorbents, and examining alternate bed configurations to improve system efficiency and reliability. These development efforts combine testing of sub-scale systems and multi-physics computer simulations to evaluate candidate approaches, select the best performing options, and optimize the configuration of the selected approach, which is then implemented in a full-scale integrated atmosphere revitalization test. This paper describes the development of atmosphere revitalization models and simulations. A companion paper discusses the hardware design and sorbent screening and characterization effort in support of the Atmosphere Revitalization Recovery and Environmental Monitoring (ARREM) project within the AES program.