Group processes become highly complex with increased crew heterogeneity. The personality traits and attitudes for successful performance during long-duration missions may be different from optimal characteristics demonstrated on short-term flights. It is important to identify the factors predictive of the long-term psychological stability of individual crew members who might be subjected to prolonged periods of acute or extended chronic stress. Countermeasure strategies need to be re-evaluated within the context of the psychological demands of coping with extended periods away from usual sources of social support. Selection of crew members with psychological and group process training is advisable.