Needed: Star-trekking family for space odyssey

Nasa scientists are thinking the unthinkable. They are contemplating what it would take to send a spaceship full of men, women and children to colonise an Earth-like planet that is orbiting a distant star.

The mission – should anyone be brave enough to accept it – is to be part of a close-knit community of space pioneers who will turn their backs on Earth for good. They would do so in the knowledge that only their great, great, great grandchildren might ever stand a chance of returning.

Yesterday at the American Association for the Advancement of Science (AAAS) some of the technical, ethical and emotional difficulties of interstellar space travel were aired

Geoffrey Landis, a rocket scientist at the US National Aeronautics and Space Administration's Glenn Research Centre in Cleveland, Ohio said: "This is really the first science meeting that looks at the question of what do we need to do to go beyond our solar system, to ask how do we send astronauts to another star?"

Dr Landis described how over the past three years an almost "underground" movement of star-trekking scientists within NASA have become respectable thinkers.

"For years, NASA's official stance on interstellar travel was to ignore the subject and pretend it didn't exist. Some of the scientists at Nasa would work on it in their spare time but there wasn't any funding to do that. In the last maybe three or four years that's changed," Dr Landis said.

Heavily criticised for not thinking creatively beyond the next five or ten years, NASA has set up an Institute for Advanced Concepts to study bold, new initiatives in space exploration that go well beyond the first decade of the 21st Century.

With the discovery over the past five years of more than 70 "extrasolar" planets orbiting other stars, the idea of sending probes and even people to explore an Earth-like planet, if such a habitable world is ever found, gained respectability.

"Perhaps 20 years ago everybody would have said, no, it's impossible to travel to the nearest star. It requires too much energy." Dr Landis said.

"But a number of very clever people have been chipping away at the problem and I think now we can answer: yes, it would be very difficult but it should be possible without breaking the laws of physics to send probes to the nearest stars," he said.

No one, least of all the NASA scientists analysing the problem, underestimates the difficulties of travelling four light years separating Earth from the nearest stars, Alpha Centauri and Proxima Centauri.

John Moore, an anthropologist at the University of Florida dismissed the idea – popular in science fiction comic books – that interstellar spaceships should be crewed by heterosexual men living side by side for years. That, he said, would fulfill all the conditions necessary for murder.

Given that it would take a minimum of several centuries to make a return trip to the nearest star, it would mean planning for a community to reproduce for least six to eight generations, Dr Moore said.

"As a starting population for the space crew, we can use a group of young, childless married couples, instead of a population comprising all ages and both sexes," Dr Moore said.

Genetic considerations dictate that the crew of about 200 men and women should be as varied possible to avoid the dangers of inbreeding. This would mean choosing the crew from a wide ethnic mix but who all speak the same language, said Sarah Thomason, a linguist at the University of Michigan.

But the real problem is how to get there. The two Voyager probes, launched in the 1970s and, at a speed of nearly 33,000mph, travelling faster than any space object launched by man, will still take 75,000 years to reach the nearest star.

One idea is to build an interstellar spaceship that is accelerated to velocities approaching 10 per cent of the speed of light by firing pulses of laser light at a set of giant sails made of ultra-thin films of artificial diamond.

The laser itself would remain in orbit near Earth. The spacecraft, which would be the size of a city would travel on the laser energy at speeds that far exceed those achieved by conventional rocket technology.

Parking the laser in orbit would mean that the heaviest part of the spacecraft's propulsion system – its engine – is left behind, making the vehicle lighter than it otherwise would. Two problems with the form of propulsion are: how to brake and how to get back to Earth once you've arrived. Stopping may take up to 100 years to achieve.

But who on Earth would want to volunteer? "It might be people searching for religious freedom, that certainly has been a theme of colonisation," Dr Landis suggested.

"It might be people who have their own ideas of government and want to set up a new government. Or it could be that people would just want to escape the planet because they think there is a better life out there in the stars."