Issues and challenges of space radiation risk assessment in manned deep space exploration missions

Abstract

The plan and implementation of manned deep space exploration missions should first ensure the health and safety of astronauts. Space radiation, mainly coming from galactic cosmic rays (GCR), solar particle events (SPE) and trapped belt radiation (TBR), has been generally considered to be one of the most important risk factors threatening the health of astronauts in deep spaceflight missions. Health risks from these exposures mainly include four aspects: carcinogenesis, acute radiation syndrome, central nervous system damage and degenerative tissue effects, and the risk of carcinogenesis remains a primary concern for manned deep space explorations. The difference in the radiation environment between the deep space and the ground leads to a high uncertainty on the estimated health risk, which is currently the main hindrance to manned interplanetary exploration. The issues and challenges related to health risk assessment of space radiation for astronauts during manned deep space exploration missions are systematically summarized and analyzed in this paper. Six main issues were raised in space radiation risk assessment, including estimation of space radiation quality, extrapolation of low-dose/dose-rate radiation risk, prediction of dose- and dose-rate reduction effectiveness factor (DDREF), screening of differences in individual radiosensitivity, effects of microgravity and other stressors on space radiation risk, and assessment of acute radiation syndromes caused by SPE. In addition, six corresponding key technologies were also discussed to address these scientific issues and challenges for future studies and practice: (1) The more dose-response data in experimental animals is needed for estimating the relative biological effectiveness (RBE) for different high-energy charged (HZE) particle types in different tissues. (2) The improved radiobiological models including targeted and non-targeted effects models, are required for accurately estimating space radiation quality factors. (3) It is necessary to accurately estimate the DDREF for low dose and dose-rate radiations, and it should be further comfirmed whether the linear-no-threshold (LNT) model is the most appropriate way to extrapolate risk estimates in low dose and dose-rate through more relevant theoretical and experimental researches. (4) The biomarker selection techniques are important to identify the potential biomarkers associated with space radiation, and the integrated risk assessment models based on the space radiation sensitive biomarkers using systems biology approaches can improve the accuracy of predicting individual radiosensitivities and disease risks induced by space radiation. (5) The influence of microgravity and other stressors on space radiation risk need to be further investigated. (6) More accurate SPE prediction models and the corresponding acute radiation risk assessment models are also necessary in further studies. The goal of reducing the uncertainties in space radiation risk assessment can be fulfilled by an international co-operative effort in these critical technologies. The arrangement and analysis of the critical issues and key technologies of space radiation risk assessment in manned deep space exploration missions can provide the strategies of reducing the health risk of astronauts induced by space radiation.