At the European Space Radiation Shielding Workshop 2026, held 17–18 June 2026 at ESA/ESTEC, researchers evaluated lunar-surface radiation using Geant4 Monte Carlo simulations covering maximum Galactic Cosmic Radiation (GCR) intensity and historical Solar Particle Events (SPEs), including the NASA reference event. More than 4 g/cm² of lunar regolith reduced SPE exposure below current 30-day limits, while approximately 180 g/cm² produced an estimated total dose equivalent of 200 mSv/year—about 35% below the estimated unshielded exposure.[1][2]
The result separates two hazards. Regolith is highly effective against short, intense SPEs but additional mass shielding provides little reduction in absorbed GCR dose; at 180 g/cm², chronic exposure remains approximately 200 mSv/year. The workshop also presented CIRA’s multifunctional multilayer composite using hydrogen-rich polyethylene and ultrahigh-molecular-weight polyethylene fabrics, designed to combine radiation mitigation with structural performance at lunar temperatures up to 120 °C.[1][5]
The Ark team should establish a layered radiation architecture: bury primary habitats beneath at least 4 g/cm² of verified regolith for SPE protection, engineer substantially greater mass where practical, and develop hydrogen-rich composite barriers for walls, pressure vessels, equipment, and storm shelters. Radiation models must track GCR-induced cumulative dose, SPE warning-to-shelter timelines, material degradation, secondary-particle production, and the exposure limits applicable to multi-generational residents and archived biological systems.[1][2]