Application of Computational Methods for Radiation Damage Mitigation and Prediction in the Space Environment

Abstract

The space radiation environment consists of multiple complex sources of radiation that reduce the overall performance of satellite systems. As a result, there is a continued need for new opportunities to increase the resiliency of satellite systems against the harmful effects of space radiation. In this work, computational simulations of radiation-matter interactions are explored in two research thrusts that address the mitigation of space radiation damage to satellite systems from a materials perspective.In the first research thrust, Monte-Carlo simulations were carried out to inform radiation shielding design for the low-Earth orbit (LEO) environment. These simulations can be used to identify optimal radiation shielding materials and designs to protect satellite devices from radiation damage. In particular, GEANT4 (Geometry And Tracking) was used to simulate the performance of 3D printable metal-polymer composite shields in a combined proton and electron environment consistent with LEO trapped particle radiation. Copper-particle-loaded-polylactic acid (Cu-PLA) was used as a model system of a metal-polymer composite. This effort confirmed that simulation-informed radiation shielding design cannot rely on simplification of the more complex, combined LEO radiation environment, despite the opportunity for reduced computational complexity and increased speed. The Monte-Carlo simulations were also successfully used to assess the radiation-matter interactions that took place within the Cu-PLA shields, providing useful insight into the underlying mechanisms contributing to shield performance. Findings, of broad interest to LEO shield design, included the optimization of Cu-PLA shield thickness needed to shield against LEO trapped electrons, an appreciation for the overriding contribution of the trapped proton flux in determining the total ionizing dose behind the shield, and the development of a length-scale metric useful in early assessment of the relative effectiveness of Cu-PLA shielding in attenuating trapped protons incident flux. Additional insight into the structural ramifications of radiation-matter interactions was obtained in the second research thrust. In this case, molecular dynamics (MD) simulations and structural analysis methods were pursued to establish an initial modeling methodology to assess radiation damage in inorganic oxides, typically used as the basis for space-based optical systems. Specifically, the LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator) MD code was used to perform displacement damage simulations involving a single oxygen primary knock-on atom (PKA) in α-quartz. Oxygen PKA energies of 1, 2, 4, and 6 keV. Displacement damage in α-quartz was assessed by analyzing changes in the coordination number, atomic displacement, and bond angle/length distributions before and after the system was irradiated. It was determined that the number of under-coordinated, over-coordinated, and atomic displacement defects increased with increasing oxygen PKA energy. Notably, the PKA produced more under-coordinated Si and oxygen defects than over-coordinated ones for all energies. A power function yielded a good fit in modeling the relationship between the number of under and over-coordinated defects produced and the initial oxygen PKA energy. The full-width-at-half-maximum of the bond length/angle distributions also had a positive correlation with oxygen PKA energy. The results from this application illustrate a preliminary effort to predict the effects of displacement damage on the point defect structure in oxides. Such results, when used as the basis for subsequent quantum-based models (e.g. density function theory (DFT) and time-dependent DFT (TD-DFT)), offer a path toward the prediction of radiation-induced optically active defect state energies and populations, and the ensuing optical performance modifications, of space-based optical materials.