Are space elevators possible? Physicists say they can turn humanity into a ‘space-faring civilisation’
This article has been reviewed in accordance with Science
Credit: Pixabay/CC0 Public Domain
Credit: Pixabay/CC0 Public Domain
Humanity’s quest to explore, and perhaps eventually colonize, outer space has stimulated many ideas about precisely how to do just that.
While conventional wisdom suggests that rocket space launch is the best way to send humans into orbit, other “non-rocket” methods have been proposed, including a futuristic “space elevator.”
The concept of a space elevator — essentially a cable reaching into the sky that allows humans to ascend into space — has been championed by some industry experts as a way to overcome the astronomical costs associated with sending people and cargo into space with rockets, says Alberto D. La Torre is an assistant professor of physics at Northeastern University.
“Current launch systems are mostly single-use and typically exceed $10,000 per kilogram of payload, totaling about $60 million per launch,” says de la Torre. “This is where space elevators become attractive.”
The space elevator, first envisioned by Russian rocket scientist Konstantin Tsiolkovsky in the late 19th century, would extend from Earth through the atmosphere, then beyond “geostationary orbit,” the altitude at which objects in space — pulled by Earth’s gravity — orbit. About more or more orbit. Lower along with its rotation. Geostationary orbit is located approximately 22,236 miles above the Earth’s surface.
Effectively, the cable will descend from the structure of a satellite installed in geostationary orbit which will act as a “counterweight” to the Earth.
In theory, a satellite placed outside geostationary orbit would stabilize the cable through a combination of forces: the pull of Earth’s gravity, which would force it downward from Earth, and the centrifugal force of its rotation, which would exert Upward force. The force on the cable from space. De la Torre says the interplay of forces would create the ideal tension—strain—necessary to maintain a cable of that length.
“The key element of the space elevator is its cable, which is positioned at the Earth’s equator and synchronized with the Earth’s rotation,” says de la Torre.
There is no proof of concept for a space elevator. While there have been several attempts at architectural designs, including an award-winning design by a British architect that recently received a six-figure award, several technical hurdles have kept a space elevator out of reach for decades.
“A cable of this length (more than 22,236 miles above Earth) is not possible using standard materials,” says de la Torre. “If they were made of steel, the maximum stress they experience in geostationary orbit would exceed the tensile strength rating by more than 60 times.”
For a ground-based space elevator, strategies to reduce tensile forces, or the ability of a material to withstand tension, are critical, he says.
But there are some materials that hold promise. Boron nitride nanotubes, diamond nanofilaments, and graphene — all materials with “low density and high tensile strength” — could fit the bill, de la Torre says.
“Carbon nanotubes have been proposed as an ideal material because of their high tensile strength,” he says. “Recent research has raised concerns about the feasibility of translating their nanoscale properties into macrostructures.”
In the long term, the promise of a space elevator lies in its ability to make journeys into outer space significantly more economical. “The cost of placing a payload outside geostationary orbit can be reduced to a few hundred dollars per kilogram,” says de la Torre.