Radiation risk mitigation in human space exploration: a primer, a vision, and the state of the art

Human exploration beyond low Earth orbit poses unique health and operational challenges, with space radiation recognized as one of the most significant hazards. This comprehensive review examines the complex nature of the space radiation environment, its biological effects on humans and life support systems, and current strategies for risk assessment and mitigation. It details the composition and properties of galactic cosmic rays (GCRs) and solar particle events (SPEs), their interactions with spacecraft shielding, and the resulting biological impacts ranging from DNA damage to systemic effects including cancer, cardiovascular disease, and central nervous system impairments. Special emphasis is given to the combined effects of radiation and microgravity, which together alter cellular function and influence health outcomes. The paper also explores the effects of radiation on plants and microorganisms as biological components of bioregenerative life support systems (BLSS). The issue of radiation-induced degradation of food and pharmaceuticals is also considered. Existing and emerging countermeasures, encompassing passive and active shielding, pharmacological agents, nutrition, physiological adaptations like synthetic hibernation, and personalized risk assessment through targeted crew selection are critically reviewed. Additionally, the work highlights the importance of high-fidelity analog studies, space-based experiments, and advanced risk models integrating physical, biological, and operational data to inform future mission planning. Finally, the paper reviews existing infrastructures, experimental platforms, and European research programs, emphasizing the critical role of ground-based accelerators, space analog environments, and in-flight studies in advancing our understanding of radiation risks. By identifying key knowledge gaps and proposing a structured mitigation framework, this study presents a strategic roadmap for protecting human health and sustaining life during long-duration missions to the Moon, Mars, and beyond. (The review work described in the paper stems from the discussions within the working group on Radiation sponsored by the Italian Space Agency.)