Fly me to the moon - some time this century, space tours could be possible

If extreme sports such as parachuting off high bridges and skiing off mountain peaks are not enough to keep the heart racing, then consider a trip into orbit.

You shouldn't have to wait too long for the opportunity. The technology exists to send tourists into orbit, according to a NASA specialist, but there is as yet no way to do it commercially.

Space tourism will come in time however, built on the back of private enterprise, according to Prof Yoji Kondo, an astrophysicist at the NASA Goddard Space Flight Centre.

Studies in the US have shown there are plenty of takers for a flight into space, he says. One survey suggests more than a third of regular air travellers in the US would buy a seat on the space shuttle and one in 10 is willing to spend $100,000 for a ticket. Tourists are already spending up to $10,000 to fly to Antarctica, which showed there is a market for this type of adventure travel, Prof Kondo says.

Up to 20 companies are re searching reusable launch vehicles to carry tourists into space, and if space travel for all was to come, it would most likely be delivered by the private sector. "The technology is probably there but it is not packaged suitably for a space ship. In principle, those people working in the field say they don't need breakthrough technology," he says.

What would tourists find on the moon or Mars? Perhaps a forest or familiar plants, genetically engineered to produce a welcoming habitat, suggests Prof Freeman Dyson of the Institute for Advanced Study in Princeton.

He was asked to speculate on technology in 50 years. The 21st century will be dominated by advances in the biological sciences, he says, and humans travelling to distant planets would need new habitats.

"The way to do it really is to grow the habitat on Mars rather than build it." Trees could be genetically modified to a protective habitat which could be occupied by the space traveller.

"NASA is very much encouraging commercial developments in all our activities," Dr Kathie Olsen, NASA's chief scientist, says. The space agency is also investing large sums into research that would allow humans to tolerate long space flights.