This chapter reviewed some of the ways in which interpersonal and small-group variables may affect crew performance and the quality of life in space. A central theme in the literature has been choosing as crewmembers people who are compatible in the sense that their abilities, interests, and motives prompt them to act in ways which other crewmembers consider desirable and appropriate Almost nothing is known about all-female or mixed-sex groups operating under conditions of isolation, confinement, and risk. On the one hand, mixed-sex crews offer social diversity; on the other hand, sex-role stereotypes and negative attitudes toward astronauts of the opposite sex could prove disruptive. Further research is necessary to discover patterns of interaction within all-female and mixed-sex crews, and to ensure that crewmembers are flexible and tolerant in their dealings with members of the opposite sex. Moreover, means must be sought to minimize the potentially disruptive effects of pairing-off and to ensure that sexual expression assumes acceptable forms.
The available evidence suggests that there may be certain advantages to including both relatively young and old members among a crew. Desirable age mixes need to be better understood. In addition, we need to know more about adult development under spaceflight conditions.
It is expected that social change coupled with a growing likelihood of international missions will increase cultural heterogeneity within spacecrews. The intergroup relations literature specifies certain conditions which are likely to reduce prejudice, and many of these conditions can be established in space. In addition to prejudice, problems include language or communication difficulties and differing, culturally related preferences regarding food, facilities, and activities. Further research is a prerequisite for achieving coordination within ethnically mixed crews.
 A number of personal qualities have been found to be of high value to most members of isolated and confined groups. One such quality is personal attractiveness. It should prove useful to select-out individuals with characteristics that most other crewmembers will find aversive and individuals who find too many human qualities aversive. Second, emotional stability is very important. Future screening procedures must extend beyond selecting-out emotionally unstable candidates, and select-in candidates of exceptional psychological health. Perceived emotional stability may be as important as actual emotional stability, so it is necessary to study the psychological processes upon which judgments of emotional stability rest. Third, a high level of technical competence is crucial, especially for leaders. Competence research should be extended to include interpersonal as well as technical competence, and, as in the case of emotional stability, research should be expanded to include perceptual and judgmental processes.
Two other important qualities are cooperativeness and social versatility. Research regarding own-gain, relative-gain, and joint-gain motivation may be of use, as people with joint-gain motivation may prove to be of value in the highly socially interdependent setting of space. Perhaps even more important is further work to bridge achievement motivation and cooperation. Research in this area suggests that need achievement subsumes three variables known as work orientation, mastery orientation, and competition. It is hypothesized that individuals who are strong on work orientation and mastery orientation but weak on competition will best serve the joint task and socioemotional requirements of space. This hypothesis requires additional study under conditions analogous to those found in space.
The conditions of spaceflight will restrict the opportunity to enter into varied social relationships. Thus, social versatility may also be an asset in space. Relevant here are studies of individual differences in the ability to perform both the task-oriented masculine role and the socioemotionally oriented feminine role. Additional research is required to better understand the consequences of androgyny under spaceflight conditions, and to identify additional traits which might be related to social versatility.
Our discussion of social compatibility then turned to an examination of similarities and differences among crewmembers. It has repeatedly been found that attitudinal similarity is a powerful determinant of interpersonal attraction. However, extreme attitudinal homogeneity may cause boredom and undermine a crew's  problem-solving potential. A major issue is identifying conditions under which consensus is preferable to diversity, and conditions under which diversity is preferable to consensus. Also, interlocking abilities and needs are expected to contribute to compatibility. Relevant to the former are skill complementarily and cognitive complementarily; although these variables have appeared in theoretical discussions, they are not well researched. Relevant to the latter are congruent, complementary, and competitive needs. Although some progress has been made studying such needs, it is time to consider a comprehensive program to identify relevant needs, discover how they fit together, and demonstrate the consequences of compatibility and incompatibility.
Russian researchers report that people differ in the extent to which they can effectively coordinate their activities in certain kinds of experimental social situations. Accompanying a high degree of interpersonal coordination in voluntary responses is the synchronization across group members of certain nonvoluntary psychophysiological responses. The Russians suggest that groups whose members develop such synchronicity tend to do well under spaceflight conditions and to be particularly well suited for dealing with danger. This intriguing line of research needs to be replicated and extended in the West.
Because increasing crew size should be associated with an expanding array of social options, crew size is expected to correlate positively with crewmember satisfaction. However, the data on this point tend to be anecdotal and are all to often confounded by variables other than group size. A thorough understanding of the effect of crew size on crewmember satisfaction awaits the results of studies of different sized groups operating under spaceflight-like conditions.
In concluding our discussion of social compatibility, we proposed a shift in emphasis from selecting crewmembers on the basis of their individual characteristics to selecting entire crews on the basis of their combined characteristics. This is desirable because com- compatibility depends in part on the intermeshing of different people's qualities and upon different people's perceptions of and attitudes toward one another. Accompanying this shift are many complex theoretical and methodological issues. To compose large crews, and to staff multiple missions, we will have to devise reliable and valid means for assessing large numbers of people in relatively brief periods of time.
 Strong demands will be placed on crewmembers who occupy leadership roles, and the penalties for incompetent or weak leadership will be high. Our discussion of leadership began with the common distinction between task and socioemotional leadership activities. Case histories suggest that under conditions of isolation, confinement, and risk, a leader can perform both task and socioemotional leadership roles, but influential reviews of leaders in everyday environments show that normally the two roles are differentiated. Future research must address different divisions of task and socioemotional activities within spacecrews. One possibility for reconciling conflicting claims is that under conditions of isolation, confinement, and risk, people have a strong defensive need to perceive their leaders as competent on all dimensions.
Contemporary leadership theory focuses upon the interaction of structural and personality variables rather than upon either variable alone. The most influential theory is contingency theory, which suggests that situational favorableness and leadership style combine to determine leadership effectiveness. This theory posits that task-oriented leaders are maximally effective under conditions of extremely high or extremely low situational favorableness, and that socioemotionally oriented leaders are maximally effective under conditions of intermediate favorableness. Tomorrow's missions are likely to vary in terms of their situational favorableness, and on any given mission, situational favorableness may decline over time. Additional research is required to achieve a good match between situational favorableness and leadership style throughout the course of future flights. Researchers should consider an expanded range of leadership alternatives, and should remain sensitive to the possibility that no single decision-making structure will prove "best" for all purposes.
Most analyses describe group cohesiveness or unity as resulting from the rewards of group membership. We expect morale to be high when crewmembers are working toward well-defined superordinate goals. It is hypothesized that such distant goals should be supplemented by interim goals. Through reducing the costs of group membership, task and socioemotional training should also raise cohesiveness. Investigators must also examine the procedures that astronauts can use to diagnose and contain on-board frictions. Also relevant to understanding spacecrew cohesiveness is manning theory, which explores the consequences of involving few people or many people relative to the job to be performed. Early findings suggest that there may be both psychological and social benefits when the number of  participants is slightly less than normally expected, given the task demands. Manning theory requires particularly careful study prior to possible application in space-capsule microsocieties.
Many complex issues surround compliance and conformity. Social pressure is essential for interpersonal coordination. However, rejection or ostracism may produce unacceptable personal consequences in space. Further research is necessary to find ways of softening the potentially adverse effects of conformity pressures and to find ways to reintegrate deviants into the crew. Conformity pressures can also restrict the flow of innovative solutions to problems. Additional research is required to understand the development and control of "groupthink" under spaceflight conditions. A similar problem to combat is an unquestioning attitude in a leader's presence. Training procedures must be found to help crewmembers separate useful from distracting decision-making input, and to ensure that leaders are receptive to the useful input.
Group performance reflects a complex interplay of many different factors. According to the Hackman and Morris (1975, 1978) process model of group performance, there are essentially three techniques for developing efficient and effective crews. These are (1) composing crews in such a way as to ensure a good representation of the desired technical and social skills, (2) structuring tasks in such a way as to maximize motivation and commitment, and (3) manipulating social norms to encourage the development and use of appropriate performance strategies. These techniques need to be evaluated as applied to isolated and confined groups that are operating under conditions of risk.
Both recently formed (young) crews and well-established (mature) crews offer advantages and disadvantages. Ideally, a crew entering space would be young in the sense that the members have not yet become bored with one another but mature in the sense that they have achieved a high degree of interpersonal coordination. Additional research is required to identify ways to simultaneously achieve a high degree of social variety and interpersonal coordination. Finally, certain types of crews will have rotating membership. A central issue here is identifying ways to ease the integration of newcomers into crews. It is hypothesized that the process of assimilation may be eased if newcomers undergo preentry therapy, are sponsored by specific crewmembers, and/or are in frequent telecommunication with the crew prior to their own visit to space. Training crewmembers in space itself may help novices adapt to the conditions of space and facilitate the transition to operational status.