But the physical danger was judged to be less important than the psychological stresses.  Eight humans, crowded together like monkeys for almost three Terran years, had better get along much better than humans usually did.  An all-male crew had been vetoed as unhealthy and socially unstable from lessons learned earlier.  A ship's company of four married couples had been decided on as optimum, if the necessary specialties could be found in such a combination.