In the first ten years of the U.S. space program, space missions had no more than three individuals, were exclusively male, and were drawn from the ranks of test pilots or scientists with pilot experience. In the future, missions may be mixed ethnically, culturally, and may also include women. Individuals may not be exclusively pilots, and extended missions may need professionals from other fields of expertise, such as doctors, engineers, or specialists for experimentation and research. The field of psychology has analyzed extensively the group setting and interpersonal dynamics. Because of the amount of time that members of a mission spend in space with limited communication from Earth, small changes in the environment, and no direct access to different individuals, psychology should be interrelated with concerns on the dynamics of human emotion and individual motivation and productivity in spaceflight.
Psychology also studies how an individual's environment affects performance.
Psychological problems that can strike long-duration astronauts include anxiety, emotional hypersensitivity, insomnia, irritability, and depression. The prospect of crew heterogeneity and significantly longer assignments will affect the astronaut selection process. The psychological criteria of the selection process should also measure an individual's capacity to adapt to a new physical environment for extended periods of time while simultaneously maintaining effective performance. Fortunately, humans tend to be very adaptive and flexible psychologically. However, astronauts must be kept psychologically as well as physically sound during their journey.