SPACE ELEVATORS Astronauts soaring into space on a 40,000 km-high elevator may seem like a futuristic fairy-tale, but space travellers may one day ditch rockets in favour of 'Jack and the Beanstalk'-style transport.

Science fiction or fact?

Strangely enough, the idea for a space elevator was first conceived over 100 years ago by a Russian scientist called Knostantin Tsiolkovsky, who imagined a 'celestial castle' built at the pinnacle of giant tower.

When will we build space elevators? Probably about 50 years after everyone quits laughing. Arthur C. Clarke

In the late 1970s, sci-fi guru Arthur C. Clarke, inspired by a technical paper, imagined an elevator that could stretch into space. He penned a novel called 'Fountains of Paradise', describing a quest to construct a tower on a tropical island that reached up into the clouds and beyond.

As is often the case, science fiction inspired science research. In 2000 space elevators were debated at a NASA conference. The outcome was a proposal to build a base tower 50km high, with a cable tethered to the top reaching into space. The other end would be anchored to a counterbalance, perhaps a space station, or a cosmic hotel. One ambitious plan involves lassoing an asteroid to the other end of the cable to keep it stable.

NASA describe the space elevator as a feasible and highly desirable future goal. The most expensive part of a current spacecraft's trip is the launch into orbit. A permanent lift system would make rocket-powered launches redundant, opening the way for cheaper space exploration and tourism.

How it would work

In order to transport passengers up the tower, magnetic tracks would be laid up the side to grip floating space trams called 'maglevs' (short for 'magnetically levitated' vehicles). These trams would transport people and payloads into space at thousands of kilometres an hour. Just as Clarke forecast, the cables could be constructed from tough new fibres called carbon nanotubes, as strong as diamonds, but far less expensive.

Low-cost space travel

Space elevators could slash the cost of jetting off into space. Currently sending a tourist (including baggage) on the shuttle costs around £60,000. A trip on the space elevator could cost a mere £150. However, don't start packing your moon boots yet. NASA doesn't expect the necessary technology to be ready until the end of the century.

As for the man himself, when asked when he thought his fictitious elevators would be built, Arthur C. Clarke replied, "Probably about 50 years after everyone quits laughing."