A novel, population-based approach to astronaut radiation risk assessment

Abstract

Risk due to space radiation exposure is one of the prime concerns for astronaut health and safety on deep space missions. NASA's current radiation risk limit is 3% risk of exposure-induced death (REID) at the upper 95% tolerance limit. Sex and age dependence in existing radiation risk models and large uncertainties, mostly due to lack of knowledge of biological effects of highly energetic and heavy charged particles, presently limit demographics to older, male astronauts for participation in long-duration missions to Mars. To address this issue, a novel method is introduced for evaluating radiation risk for proposed missions, where the combined risk for the population is used in place of age- and sex-specific risks. The age and sex distribution of active and trainee astronauts as of 2018 and operational NASA tools for evaluating astronaut radiation risk are used to demonstrate the proposed method for a variety of missions. Discrete and continuous methods representing the population probability density function are tested. Mission-specific astronaut population risk distributions are constructed using random sampling from the astronaut age and sex distributions, which are then used to calculate the corresponding upper 95% tolerance limit. It is found that the population-combined REID for a conjunction class Mars mission in solar maximum conditions is around 4% at upper 95% tolerance limit, which is less than the REID for female astronauts of age less than 55 years. It is also found that the probability density function and organ-specific risks for the population-combined REID are very close to that of 30-year-old male and 60-year-old female astronauts. The present work demonstrates a methodology for performing space radiation risk assessments independent of astronaut age and sex.