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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.
Material for
Space Elevator -- Cable Construction
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.
Designs
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.
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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