2002-02-16 08:39:57 -- By BBC News Online's Jonathan Amos in Boston
Unlike today's relatively small space vehicles such as the shuttle, the cosmic craft of tomorrow will have to be the size of small cities and be constructed in orbit.
Researchers gave their suggestions on how we might explore other star systems to the annual meeting of the American Association for the Advancement of Science in Boston.
They said the 200 or so volunteers who went on a mission would have to realise that they were taking up a one-way ticket and would most probably never live to see the ship's final destination.
It is only in the last few years with the confirmation that planets do exist outside our Solar System that scientists have done some serious speculation on how we might visit distant worlds.
American space agency researcher Dr Geoffrey Landis said the Earth had a finite lifespan - the Sun will eventually burn itself out - and if humans wanted to carry on they would need to move to a new home.
But transporting large numbers of people across the galaxy would require vast vessels driven by gigantic sails, blown across deep space by intense bursts from a giant laser.
"You could have a sail that is perhaps hundreds of miles across," he told the BBC. "It would be huge but extremely light and then the colony itself that's being pulled by the sail would be just a tiny little speck compared with this enormous sail. It would glide serenely through space, lit up from time to time as the sail hit dust particles on the way."
The researchers are trying to foresee the sorts of social problems that might arise on such a mission. Linguistics expert Professor Sarah Thompson, from Michigan University, believes the colony could soon have difficulties communicating with Earth.
"Let's say you start with one language - perhaps English," she speculated. "After 500 years, English will have changed so much on Earth and so much, and completely independently, on the spaceship that they will be mutually unintelligible.
"So, you'll have space English and Earth English and they won't be able to communicate."
An interstellar ship would be like an ark, carrying everything the colonists might need, including greenhouses for growing food and sophisticated manufacturing facilities.
Anthropologists think it could be important for the crew to be composed of a variety of nationalities to increase the size of the gene pool. And it is entirely possible that if these humans remained in reproductive isolation for long enough, they could evolve into another species altogether.
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