Are There Limits to Man's Long-Term Presence in Space?

Manned space flight, now entering its third decade, has been proven to be feasible and endurance has steadily and incrementally increased from hours and days to over six months. None of the physiological changes noted to date has proven detrimental to health. As we now move toward a more permanent presence of man in space, knowledge and understanding of causative factors will become important to assure man's performance capability of tasks which will become more varied and increase in complexity. Psychological well-being and nature of the proposed habitat must receive important considerations in future overall system design. In order that Space Stations reach their fullest potential, they must be open to the greatest segment of the population which may include older aged individuals, females, and individuals with known disease states. Preliminary ground-based simulation studies using these groups have shown no reason for concern, but have been limited to a small number of tested subjects and to periods of study less than six months. Progress will require attention to subtle changes as well and use of appropriate animal studies.