How will space elevators work

A.� The elevators will span a continuous 47,000 kilometres, with a space station placed at 35,786 kilometres, a specific distance at which 'geostationary' orbit can be achieved. At this special distance the space station will take exactly one day to orbit the Earth, and, if the space stations orbit is aligned with the equator then, it will hover over the same point on Earth's surface as the two turn together.

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The space station will act as the elevators centre of mass. Those parts of the space station closer to Earth will be moving around it more slowly than necessary to maintain a stable orbit, and so will pulled by Earth's gravity. Those part of the space station further away from Earth will be moving too quickly around it for their distance and so will try to move further afield, like a stone in a sling. The net result will be cable pulled taut by the tension of the opposing forces.

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Q.� When could space elevators start going into production

A.� Although it's theoretically possible, sending an elevator into space would pose one or two technological teasers. But, two independent NASA teams recently thought these through and estimate that work on the space elevator could start by the end of this century.

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Q.� What technological hurdles need to be overcome

A.� Mainly, finding a material suitable for a cable that has to dangle from the space station to Earth. Such a cable would have to be incredibly strong whilst also able to support its own enormous weight over a vast distance, whilst only being a few centimetres in diameter. Up until recently anything like a suitable material just didn't exist.

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However carbon, from which those famously hard jewels, diamonds, are formed, looks likely to provide a possible solution, in the form of nanotubes. Nanotubes are made from sheets of hexagonally arranged carbon atoms and are very strong, around 100 times stronger than steel.

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Q.� What will it be like travelling in a space elevator

A.� To start with the acceleration will push you into your seat. Then, after ten minutes this will ease as you cruise upwards at around 20000 kilometres an hour, at an altitude of 150 kilometres and rising and you'll start to feel weightless. Then, you'll just have to sit back for the next 18 hours that it'll take to reach space.

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by Lisa Cardy