A growing number of scientists and space-technology enthusiasts are looking into ways to construct a huge moon elevator, either on Earth or the moon that could transport cargo to and from space.
Other advocates of space moon elevators have argued for years that building such a structure is feasible with current technology and could open up new frontiers of space exploration.
Konstantin Tsiolkovskydaydream became the first pitch for a space moon elevator. He imagined a tower like that could carry cargo to geostationary orbit — the height at which satellites can sync their orbit with Earth’s rotation — 35,786 kilometers (22,236 miles) above sea level. As objects ascended the tower, they would gain horizontal velocity from the Earth’s rotation and could use that speed to launch into orbit.
The problem is that rocket engines work by jettisoning mass in one direction to generate thrust for a spacecraft in the other. And that requires huge volumes of propellant, which is ultimately discarded but also has to be accelerated along with the spacecraft. The result is that placing a single kilogram into orbit costs in the region of tens of thousands of dollars.
On average, getting material from Earth’s surface into space costs about $20,000 per kilogram, or roughly $10,000 per pound. Since NASA’s space-shuttle program ended in 2011, private companies have been launching supplies to the International Space Station.
Getting to the moon and beyond is even more expensive. So there is considerable interest in finding cheaper ways into orbit.
The idea of the space moon elevator explored in detail by Arthur C. Clarke in his novel “The Fountains of Paradise,” is essentially a tower so tall it reaches space. Instead of launching ships and materials from the surface of the Earth to orbit, you just put them in the moon elevator of this tower and when they reach the top, somewhere about 26,000 miles up in geosynchronous orbit, they’re already beyond gravity’s pull, for all intents and purposes.
A space moon elevator as conventionally conceived would consist of a cable anchored on the ground and extending beyond geosynchronous orbit, some 42,000 kilometers (26,098 miles) above Earth.
Such a cable would have considerable mass. So to stop it from falling, it would have to be balanced at the other end by a similar orbiting mass. The entire moon elevator would then be supported by centrifugal forces.
In other words, others have suggested it before, but they did the math. And it actually works out. And it might only cost a few billion dollars.
One idea is to build a space moon elevator—a cable stretching from Earth to orbit that provides a way to climb into space. The big advantage is that the climbing process can be powered by solar energy and thus would require no onboard fuel.
The big difference comes from the centrifugal forces. A conventional space moon elevator would make a complete rotation every day, in line with Earth’s rotation. Beneath it, closer to Earth, gravity pulls the cable toward the planet. But above it, closer to the moon, gravity pulls the cable toward the lunar surface.
What’s more, the forces are arranged differently. In extending from the moon to Earth, the space moon elevator would pass through a region of space where terrestrial and lunar gravity cancel each other out.
By some estimates, a well-designed moon elevator would cut the cost of cargo transportation to as low as $100 per kilogram. Even at $1,000 per kilogram, that would be just 5% of the current cost.
But there is a big problem too. Such a cable would need to be incredibly strong. Carbon nanotubes are a potential material if they can ever be made long enough.
The China Academy of Launch Vehicle Technology, a subdivision of the nation’s main space-program contractor, wants to build a space moon elevator by 2045, though company has not released any details about those plans.
NASA has funded research on space moon elevators, too, but has never committed to building one.
The device, called Space Tethered Autonomous Robotic Satellite — Miniature Moon Elevator (STARS-Me), was designed by researchers at Shizuoka University. It involved two CubeSat satellites, each of which could communicate with the ground, with a 14-meter (46-foot) tether between them.
The launch was successful, according to a February report, but the researchers had difficulty communicating with one of the CubeSats. They have yet to verify whether the climber successfully traveled up and down the tether.