A lunar space elevator or lunar spacelift is a proposed transportation system for moving a mechanical climbing vehicle up and down a ribbon-shaped tethered cable that is set between the surface of the Moon "at the bottom" and a docking port suspended tens of thousands of kilometers above in space at the top.

It is similar in concept to the better known Earth-based space elevator idea, but since the Moon's surface gravity is much lower than the Earth's, the engineering requirements for constructing a lunar elevator system can be met using materials and technology already available. For a lunar elevator, the cable or tether extends considerably farther out from the lunar surface into space than one that would be used in an Earth-based system. However, the main function of a space elevator system is the same in either case; both allow for a reusable, controlled means of transporting payloads of cargo, or possibly people, between a base station at the bottom of a gravity well and a docking port in outer space.

A lunar elevator could significantly reduce the costs and improve reliability of soft-landing equipment on the lunar surface. For example, it would permit the use of mass-efficient (high specific impulse), low thrust drives such as ion drives which otherwise cannot land on the Moon. Since the docking port would be connected to the cable in a microgravity environment, these and other drives can reach the cable from low Earth orbit (LEO) with minimal launched fuel from Earth. With conventional rockets, the fuel needed to reach the lunar surface from LEO is many times the landed mass, thus the elevator can reduce launch costs for payloads bound for the lunar surface by a similar factor.

 

Note:   The above text is excerpted from the Wikipedia article Lunar space elevator, which has been released under the GNU Free Documentation License.