The first concept for a space elevator was in 1895 by Konstantin Tsiolkovsky. He proposed for a free-standing tower reaching from the surface of Earth to the height of geostationary orbit. Like all buildings, Tsiolkovsky's structure would be under compression, supporting its weight from below. Since 1959, most ideas for space elevators have focused on purely tensile structures, with the weight of the system held up from above by centrifugal forces. In the tensile concepts, a space tether reaches from a large mass (the counterweight) beyond geostationary orbit to the ground. This structure is held in tension between Earth and the counterweight like an upside-down plumb bob.
To construct a space elevator on Earth the cable material would need to be both stronger and lighter (have greater specific strength) than any known material. Development of new materials which could meet the demanding specific strength requirement is required for designs to progress beyond discussion stage. Carbon nanotubes (CNTs) have been identified as possibly being able to meet the specific strength requirements for an Earth space elevator. Other materials considered have been boron nitride nanotubes, and diamond nanothreads. .In 2014, diamond nanothreads were first synthesized. Since they have strength properties similar to carbon nanotubes, diamond nanothreads were quickly seen as candidate cable material as well.
There are a variety of space elevator designs. Almost every design includes a base station, a cable, climbers, and a counterweight. Earth's rotation creates upward centrifugal force on the counterweight. The counterweight is held down by the cable while the cable is held up and taut by the counterweight. The base station anchors the whole system to the surface of the Earth. Climbers climb up and down the cable with cargo. See image below
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.
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