Sunday, December 16, 2007

Clarke Legacy: Space Elevators?

I noticed the news today that Arthur C. Clarke is 90, and celebrated his birthday at his home in Sri Lanka. He listed three wishes: for the world to embrace cleaner energy resources, for a lasting peace in his adopted home, Sri Lanka, and for evidence of extraterrestrial beings.

I decided to check out Clarke's best-known accomplishments and was intrigued by a concept called space elevators. His novel The Fountains of Paradise, in which he first described a space elevator, he believes, ultimately will be his legacy, more so than geostationary satellites, once space elevators make space shuttles obsolete.

Wikipedia says that a space elevator is a proposed megastructure designed to transport material from a celestial body's surface into space. The term most often refers to a structure that reaches from the surface of the Earth to geosynchronous orbit (and beyond). The concept of a structure reaching to geosynchronous orbit was first conceived by Konstantin Tsiolkovsky, who proposed a compression structure, or "Tsiolkovsky tower." Most recent discussions focus on tensile structures (tethers) reaching from geosynchrous orbit to the ground. Space elevators have also sometimes been referred to as beanstalks, space bridges, space lifts, space ladders, skyhooks, orbital towers, or orbital elevators.

The most common proposal is a tether, usually in the form of a cable or ribbon, spanning from the surface near the equator to a point beyond geosynchronous orbit. As the planet rotates, the inertia at the end of the tether counteracts gravity, and also keeps the cable taut. Vehicles can then climb the tether and get in orbit without the use of rocket propulsion. Such a structure could theoretically permit delivery of cargo and people to orbit at a fraction of the cost of launching a payload into orbit, and without the substantial environmental harm caused by some rocket fuels.

Recent proposals for a space elevator are notable in their plans to incorporate carbon nanotubes into the tether design, thus providing a link between space exploration and nanotechnology.
Actual cable-scale technology is currently inadequate to build space elevators, but research is ongoing, and some people believe that technology to do this may soon exist.