Are Older Astronauts Better Suited for Long-term Space Travel?

The career dose limits for Japanese astronauts are given as effective doses that are categorized by sex and age. According to this radiation protection criteria, older astronauts can be allowed to have more opportunities of staying in space. However, in line with the recommendation of International Commission on Radiological Protection (ICRP), this approach is inappropriate because the effective dose cannot be applied to an individual person, only to a nominal group. ICRP states that the requirement for sex- and age-specific radiological protection criteria could lead to unnecessarily discrimination. In addition, it is known that elderly people have generally more health problems related to aging; any person inevitably becomes vulnerable with age through various types of deteriorative changes. This fact implies that older astronauts are not necessarily more suitable for longer-term space missions. Considering these problems, we present a conceptual basis of new, broader-scope criteria where the radiological health effect be recognized as one of the equally important factors affecting health. This implies that the highest competence is to be achieved as a whole team for the success of a future deep-space mission to the moon and Mars.