space elevator
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A space elevator is a proposed transportation system that would use a cable or structure extending from Earth's surface into space to carry cargo and people into orbit, potentially making space access much cheaper and more efficient than rockets. While it remains theoretical and faces significant engineering challenges, scientists and engineers view it as potentially transformative for space exploration and commerce because it could dramatically reduce the cost of reaching space compared to conventional launch methods.
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A space elevator is conceived as a cable fixed to the equator and reaching into space. A counterweight at the upper end keeps the center of mass well above geostationary orbit level. This produces enough upward centrifugal force from Earth's rotation to fully counter the downward gravity, keeping the cable upright and taut. Climbers carry cargo up and down the cable. A space elevator in motion, rotating with Earth, viewed from above the North Pole. A free-flying satellite (green dot) is shown in geostationary orbit slightly behind the cable.
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, 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 due to the Earth's rotation (i.e., the inertia of the counterweight that creates a tension on the space side), 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. 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.