Space Elevators

When the Space Shuttle Columbia lifted off on April 12, 1981, from Kennedy Space Center, Fla., to begin the first space shuttle mission, the dream of a reusable spacecraft was realized. Since then, NASA has launched more than 100 missions, but the price of space missions has not changed. Whether it is the space shuttle or the non-reusable Russian spacecraft, the cost of a launch is approximately $22,000 per kg.

But many years prior to these events, in his 1979 novel, The Fountains of Paradise, Arthur C Clarke had written about an elevator connecting the earth's surface to space. Three decades later, this science-fiction concept is preparing to take off in the real world. NASA has launched the Space Elevator Challenge, a competition with a generous prize, and several teams and companies are working on serious research projects aimed at winning it.

As its name suggests, a space elevator is designed to raise things into space. Satellites, components for space ships, supplies for astronauts in space stations, and even astronauts themselves are examples of payloads that could be transported into orbit without the need for explosive and environmentally unfriendly rockets. A new space transportation system like this could make travel to geostationary Earth orbit (GEO) a daily event and transform the global economy. As researchers predict, space elevator would be able to carry cargo and humans into space at a price of only about $220-$880 per kg.

However, the altitude of orbital space – a colossal 35,790 km above the earth – is a measure of the challenge facing engineers. How could such a height be reached? The answer is by using an incredibly strong and lightweight cable, strong enough to support its own weight and a heavy load. It would be attached to a base station on earth at one end and a satellite in geostationary orbit (fixed above a point on the equator) at the other. Lift vehicles would ascend and descend the cable, powered by electromagnetic force and controlled remotely. The design of such a cable is still largely theoretical but current material that could be used for this purpose is carbon nanotubes. Carbon nanotubes have the potential to be 100 times strongerthan steel and are as flexible asplastic. The strength of carbon nanotubes comes from their unique structure. Once scientists are able to make fibers from carbon nanotubes, it will be possible to create threads that will form the ribbon for the space elevator. A ribbon could be built in two ways:

· Long carbon nanotubes -- several meters long or longer -- would be braided into a structure resembling a rope. As of 2005, the longest nanotubes are still only a few centimeters long.

· Shorter nanotubes could be placed in a polymer matrix. Current polymers do not bind well to carbon nanotubes, which results in the matrix being pulled away from the nanotubes when placed under tension.

The ribbon would serve as the tracks of a sort of railroad into space. Mechanical lifters would then be used to climb the ribbon to space.

The space elevator could replace the space shuttle as the main space vehicle, and be used for satellite deployment, defense, tourism and further exploration. To the latter point, a spacecraft would climb the ribbon of the elevator and then would launch toward its main target once in space. This type of launch would require less fuel than would normally be needed to break out of Earth's atmosphere. Some designers also believe that space elevators could be built on other planets, including Mars.

Дата добавления: 2015-10-29