Although the National Aeronautics and Space Administration doesn't talk about it much, mission planners do worry about mental as well as physical impacts of long-term space travel. Even a journey to Mars is expected to take nine months.
Moore noted that a Russian cosmonaut with space-station experience has warned that putting seven heterosexual adults shoulder to shoulder for nine months "provides all the conditions necessary for murder.''
While military-style expeditions may explore and conquer, Moore said the really great settlers through the ages have been organized around family and clans. "We are much less likely to go crazy in space and much more likely to accomplish our interstellar missions if we send crews into space that are organized along family lines,'' he said.
He said the best model he could find for selecting a crew comes from the ancient Polynesians. They sent flotillas of canoes filled with young but childless couples off to find new islands across the Pacific.
Moore figures that a starting population of 150 to 180 would be sufficient to sustain itself at the same rate over six to eight generations, with everyone having the opportunity to marry someone close to his or her age.
Dennis O'Rourke, a genetic anthropologist at the University of Utah, said that number could be as low as 80 without the population suffering adverse genetic consequences from inbreeding.
Moore said it would be impossible for planners back on Earth to predict what sort of values and beliefs the crew might bring back after the centuries-long sojourn. It might be necessary, for example, for returning crew members to "park" in near-Earth orbit for a few years so they could catch up on what happened on terra firma.
"This dates back to the days of the whaling ships,'' Moore said. "Men who had been gone for several years moored the ship out in the harbor and people from the community came out and told them who had died while they were away. Once they got used to all the changes, they got off the ship and went home."