Image Credit: Fredrik Johansson
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What is a space elevator?
A space elevator (also called a space bridge, or a beanstalk) is a very long, very strong cable or ribbon. One end is anchored to the Earth's surface and the other end is attached to a satellite orbiting at a height of at least 20,000 miles (36,000 kilometers).
At this height, known as geosynchronous orbit, the satellite orbits the Earth at the same rate as the earth's rotation, so it stays over the same geographical point on the ground. Communications satellites are typically found in geosynchronous orbit.
What holds a space elevator up?
Centrifugal force, balanced by gravity. Imagine holding a string with a ball on the other end. If you spin in a circle, the string will be stretched taut, and the ball will travel in a circular path. If you are the Earth, spinning around once every twenty-four hours, the string is the space elevator, and the ball is the satellite at the other end. An ant could crawl up and down the string form "Earth" to "Space" without needing wings or rockets.
Why should we build a space elevator?
Cheap access to space. Right now getting to orbit costs thousands of dollars per pound of material lifted. Expensive rockets that are thrown away after their first use, or even more expensive shuttles that require serious rebuilding after every flight.
A space elevator could cut costs by at least 90 percent. Ordinary people could afford to go to space to visit, work, and live. Orbital colonies and power stations would be possible, and interplanetary flight would be much easier.
Why haven't we built one already?
The material for the space elevator cable has to be extremely strong and lightweight. Steel is far too heavy. Kevlar, the material found in bulletproof vests, is better suited than steel, but still impractical. Even a cable of solid diamond, assuming such a thing could be made, would be too weak (not to mention expensive!). The best possibility is carbon nanotubes, three times as strong as diamond, and less dense. Nanotubes are an experimental material right now. Scientists and engineers are working on new ways to make them cheaply, in large enough quantities for projects like a space elevator, within a few years.
There are other challenges. Climbing vehicles are needed to go up and down the elevator, carrying cargo, repair patches, and eventually passengers. These vehicles must be lightweight and powerful. Imagine climbing a ladder 20,000 miles high. The StarClimber team is currently building a prototype climber, which will climb a 200 ft (60 meter) ribbon in the NASA/Spaceward.org Centennial Challenge in August.
How does the StarClimber work?
Power comes from a spotlight on the ground, which shines light up to the climber. That light is focused by a parabolic mirror onto a panel of photovoltaic (PV) cells, which generate electricity.
