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Space elevator
Proposed type of space transportation system / From Wikipedia, the free encyclopedia
A space elevator, also referred to as a space bridge, star ladder, and orbital lift, is a proposed type of planet-to-space transportation system,[1] often depicted in science fiction. The main component would be a cable (also called a tether) anchored to the surface and extending into space. An Earth-based space elevator would consist of a cable with one end attached to the surface near the equator and the other end attached to a counterweight in space beyond geostationary orbit (35,786 km altitude). The competing forces of gravity, which is stronger at the lower end, and the upward centrifugal force, which is stronger at the upper end, would result in the cable being held up, under tension, and stationary over a single position on Earth. With the tether deployed, climbers (crawlers) could repeatedly climb up and down the tether by mechanical means, releasing their cargo to and from orbit.[2] The design would permit vehicles to travel directly between a planetary surface, such as the Earth's, and orbit, without the use of large rockets.
![Diagram of a space elevator. At the bottom of the tall diagram is the Earth as viewed from high above the North Pole. About six earth-radii above the Earth an arc is drawn with the same center as the Earth. The arc depicts the level of geosynchronous orbit. About twice as high as the arc and directly above the Earth's center, a counterweight is depicted by a small square. A line depicting the space elevator's cable connects the counterweight to the equator directly below it. The system's center of mass is described as above the level of geosynchronous orbit. The center of mass is shown roughly to be about a quarter of the way up from the geosynchronous arc to the counterweight. The bottom of the cable is indicated to be anchored at the equator. A climber is depicted by a small rounded square. The climber is shown climbing the cable about one third of the way from the ground to the arc. Another note indicates that the cable rotates along with the Earth's daily rotation, and remains vertical.](http://upload.wikimedia.org/wikipedia/commons/thumb/8/89/Space_elevator_structural_diagram--corrected_for_scale%2BCM%2Betc.svg/260px-Space_elevator_structural_diagram--corrected_for_scale%2BCM%2Betc.svg.png)