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A space tether is similar to the concept of a space elevator. It’s a cable that be runs from the surface of the earth to a payload in space. The whole concept works due to the rotation of the earth and the principle of tension. Tension is a force exerted on a string keeping it straight when it’s being pulled towards the ground by gravity. In the case of the space tether, the source of tension is the centripetal force of the Earth’s rotation. Think of a toy plane with a sting attached to it. You make it fly by swinging it around your head. Several forces then act on it to keep it in position. First there is the force of tension created when you pull on the string as you swing the plane around. Then there is the speed of the plane’s movement keeping it in place. So if the conditions are right this concept can work for a space tether.
The concept is not new and has been hypothesized by scientists and science fiction writers for the past century. There has been only one obstacle to the realization of a practical space tether. That is that a cable needs to be strong enough to withstand the force of tension it will constantly endure without snapping. As of right now there are no applicable substances strong enough to meet this task.
Fortunately, new advances in the material sciences may point to a solution. Scientists have discovered a new type of carbon structure called carbon nanotubes. Carbon is an interesting element in that its properties change as its molecular structure is altered. Anyone who has seen pencil lead or a diamond knows about this. In the case of nanotubes, carbon under special circumstances can be shaped at the molecular level into tubes. This gives the carbon nanotubes a strength many times that of steel and even makes them great conductors. At the moment the biggest challenge is mass production and turning the nanotubes into a workable cable.
Despite the setbacks and obstacles, many people see space tethers and elevators as the focus of the next space race. There are even events at the X-prize competition for space technology urging teams of scientists, students, and amateurs to come up with practical solutions. The payoff s if successful will be huge. With a practical space tether we can gain access to a clean endless supply of solar energy. NASA also did some experiments to look into using space tethers laid out across the Earth’s magnetic field to generate electricity. It would also make it cheaper to send huge payloads into space making it easier to build large scale projects such as space stations and even colonies on the Moon and Mars.
If you enjoyed this article, there are several articles on Universe Today you can enjoy. First there is an interesting article about NASA working on an unfolding tether system. There is also an interesting article about a space elevator competition held in 2008.
You can also listen to Astronomy Cast. Episode 101 Advanced Propulsion systems is a great episode.