The experiment, if successful, could provide a revolutionary new way of generating power and also of launching satellites into orbit.
On Thursday, a 12-mile long space tether will be reeled out from the American space shuttle Colombia. It is little more than a strip of copper wire, one-tenth of an inch thick, encased in mixture of nylon and carbon fibre.
As it passes through the Earth's magnetic field at 17,000 miles per hour it will begin to generate electricity. The principle is the same as conventional generators, which produce electricity by passing magnets through loops of tightly wound copper cable.
Space scientists hope that the tether could be used as a means of powering space stations and craft, rather than relying on solar or nuclear power.
Tethers could also be used to winch spacecraft, satellites and equipment from one orbit to another at a fraction of the cost of using rockets. Cheap rockets would launch a payload into low Earth orbit and tethers could then winch it into a higher one.
The idea is not new. At the turn of the century, Konstantin Tsiolkovsky, a Russian schoolteacher, proposed a space railway by tethering together a series of incredible towers, anchored to the ground.
Arthur C Clark, the science- fiction writer, developed the idea by proposing that space elevators could be used to lift people and payloads into space from the Earth's surface.
The idea languished until the Seventies when Giuseppe Colombo, the Italian space engineer, gave the idea a strong practical foundation. He proposed using the tethers to build giant structures, such as space stations.
The concept is deceptively simple, but fraught with difficulties. Four years ago, Nasa tried, and failed, to produce electricity using the tethers. As an experimental version was reeled out, it kept jamming.
If they do manage to reel out the 12 miles of cable they will again encounter problems. Chief among them is the "skipping rope effect" - the uncontrolled gyrations of the tether.
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