A Launch Requirements Trade Study For Active Space Radiation Shielding For Long Duration Human Missions PDF Download

The radiation environment of space outside of Earth’s magnetic influence is one of the largest hurdles in the path to successful long-duration human space missions. High speed nuclei stripped of electrons permeate deep space and can cause irreparable damage to deoxyribonucleic acid and sensitive electronics. Permissible exposure levels set by the National Aeronautics and Space Administration attempt to limit individual occupational radiation exposures for astronauts but would be exceeded in only around half of the time a Mars mission could take. Passive radiation shielding can be effective at stopping lower energy charged particles and can help protect against high energy charged particles, but to do so completely is extremely costly as it would require an enormous amount of mass surrounding a spacecraft. Complicating matters further, passive radiation shielding can cause radiation bi-products from interactions with the initial incoming radiation, sometimes making things worse than having no radiation shielding at all. This work sought to advance current understanding in space radiation shielding interactions and to engineer a lowest-cost radiation shield for a space mission through employing the following global hypothesis: An optimized passive radiation shield for any specific spacecraft and mission can be created through the application of engineering design optimization techniques for use in space missions. The first aim characterizes the most critical radiation shielding parameters. Using a radiation transport code, we determined which materials we will likely use in further radiation shielding studies and characterize their interactions with incoming space radiation. This includes a sensitivity study on radiation shielding material selection, the quantification and characterization of radiation production and absorption in common spacecraft structural materials and radiation shielding materials, and analysis of dose and effective dose for each material model. The second aim tested several reduced order models of radiation shielding in spacecraft walls using both 1-D and 3-D geometries. A comparison of these simulations led to a key discovery regarding radiation shielding for spacecraft – in some orientations of shielding, additional shielding can increase the overall effective dose reaching the spacecraft interior. Importantly, we found that in some situations that could feasibly occur on the International Space Station, usage of a “Personal Radiation Protective System” could increase the effective dose incident on astronauts. We also found that the order with which materials are layered in radiation shielding can have a significant impact on the effective dose. The third aim demonstrated the optimization of entire spacecraft shielding models in 3-D. Optimization is conducted on a 500-day Mars flyby mission with 4 crewmembers utilizing the crew’s daily habits and necessary water cargo to reduce the amount of “parasitic” or non-mission-essential mass. This study represents the first 3-D shielding optimization study on spacecraft of its kind and determines that even with the most conservative estimates on permissible exposure levels for human safety, optimization can significantly reduce the required amount of parasitic mass. We also examined several case studies for CubeSat miniaturized satellites, optimizing the shielding placement to protect the most-sensitive electronics in an effort to extend CubeSat lifespans. In summary, the work in this dissertation has made great strides in understanding the effects of and reducing the cost of passive radiation shielding for spacecraft. We have characterized the interactions of radiation on passive shielding, creating the most in-depth catalog to date. We have demonstrated a deficiency in radiation transport using 1-D geometries that may have wide-ranging consequences for future material selection in the field. We have also shown that engineering design optimization techniques can significantly reduce the cost to protect humans from radiation in space or reduce it can be used to significantly reduce the radiation reaching inside a spacecraft or satellite compared to isotropically placed shielding. With further advances in the understanding of radiation damage to humans or specific mission designs for human or satellite missions, our optimization methods can be improved making them more accurate and cost-saving.