Getting anything into orbit today means riding a rocket, burning huge amounts of fuel to climb out of Earth’s gravity. A space elevator would replace the rocket with a cable. Anchored at the equator, it would rise straight up through the atmosphere, past the height of geostationary orbit at 35 786 kilometres, to a counterweight far beyond. Electric climbers would ride up the cable into space.
Why it would stay up
At geostationary height, an object circles the Earth exactly once a day, staying above the same point on the ground. A cable whose centre of mass sits just beyond that height would be kept taut by the Earth’s rotation, like a stone whirled on a string. The part below pulls down; the counterweight above is flung outward and holds it up. Nothing needs to be launched, and the cable itself does the work.
A long history
In 1895 the Russian space pioneer Konstantin Tsiolkovsky, inspired by the newly built Eiffel Tower in Paris, imagined a tower reaching up to geostationary height. In 1960 the Soviet engineer Yuri Artsutanov proposed the modern version, a cable lowered from a satellite, in an article in Komsomolskaya Pravda. In 1975 Jerome Pearson worked out a design in detail, with a counterweight reaching out to 144 000 kilometres. Arthur C. Clarke made the idea famous in his 1979 novel The Fountains of Paradise.
The material problem
The challenge is strength. A cable this long must hold up its own enormous weight. Engineers compare materials by their “breaking length”: how long a hanging strand could be before it snapped under its own weight. For steel it is only 20 to 30 kilometres; for Kevlar and carbon fibre, a few hundred. Carbon nanotubes and graphene could in principle reach 5 000 to 6 000 kilometres, which might be enough with a tapered cable, but nobody can yet make them in long, flawless strands.
Steps along the way
In 2009 a laser-powered climber built by the company LaserMotive won $900 000 in a NASA-backed competition by climbing a cable hanging from a helicopter. In 2018 two small Japanese satellites, STARS-Me, were released from the International Space Station joined by a 14-metre tether with a tiny climber between them. In 2012 the Japanese construction company Obayashi announced that it hoped to build a space elevator by 2050. An elevator on the Moon, with its weaker gravity, would need much less strength and could be possible with materials that exist today.