In *Radiation Protection Dosimetry* 202:8 (May 2026), a Monte Carlo study evaluated multi-purpose shelters using water, compacted waste, and polyester composites containing lithium–boron compounds against solar particle events, including the October 1989 and February 1956 storms. The best-performing arrangement placed the composite layer outside and water inside (C–W), cutting equivalent dose by 82.9%–83.1% for protons and 72.3%–73.1% for neutrons in the October 1989 event, and by 55.9%–56.5% and 33.2%–35.7% in the February 1956 event.
The technical message is that shielding order matters, not just shield mass: putting the composite exterior reduced secondary neutron production, while water remained the most practical overall shielding medium because of mass constraints and ready availability. The study also found that swapping in a LiCO3-loaded composite instead of a B4C-loaded composite improved shielding by up to 1.71%, and that a single 12.5-cm water layer produced very low modeled doses for the cases examined, with total equivalent dose lower behind water than behind comparable alternatives.
For the Ark, this supports designing storm shelters as layered, dual-use mass systems: water tanks, waste stores, and structural composites should be arranged to minimize secondary particle generation, not merely maximize areal density. The team should prioritize testing C–W and W–C configurations in lunar habitat geometry, integrate water and waste logistics into radiation architecture, and validate performance against worst-case SPE analogs such as the 1956 and 1989 events rather than relying on generic shielding assumptions.