A space elevator is any kind of solid physical connection between a satellite in planetary orbit and the planet's surface.
In practical application, space elevators are typically designed to be capable of lifting heavy loads between orbit and the surface of a planet, as this is the main economic justification for even considering such a difficult engineering task.
Space elevator designs currently focus on Earth-to-Earth orbit, as this is where transportation is currently most badly needed; in the more distant future, however, potential colonies on the Moon or Mars might also make use of a space elevator (and indeed these would be somewhat easier to construct, from an engineering standpoint).
Space elevators were envisioned for many years before any known material was strong enough to bear the needed loads; the discovery of Buckytubes shows great promise for eliminating this final hurdle, although there is still a gap to close: current designs call for a minimum tensile strength of 130 GPa (19 million psi), allowing for a safety factor of 2, while the strongest known configuration of buckytube (multi-walled) only reaches 63 GPa.
There are two major types of space elevator:
- fixed cable: the cable stays still, and compartments on it using wheels or possibly some kind of magnetic traction
- moving cable: the cable moves continuously and compartments clamp on to it to move and let go when they reach a destination
- Liftport Group "The Space Elevator Companies" -- poorly-maintained Joomla site (as of 2011-02-20)
- Space Elevators: An Advanced Earth-Space Infrastructure for the New Millennium mainly discusses intermediate designs possible with known materials
- Arthur C. Clarke - Space Elevator: Clarke discusses the space elevator for about the first half of the video
- Arthur Clarke talks about Space Elevator and Bucky: mainly historical background