thumb|350px|diagram showing equatorial and polar lunar space elevators running to . an  elevator would mirror this arrangement on the lunar far side, and cargo dropped from its end would be flung outward into the solar system. a lunar space elevator is a proposed transportation system for moving a mechanical climbing vehicle up and down a ribbon-shaped, tethered cable, in 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 currently available materials and technology. 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. ==location== there are two points in space where an elevator's docking port could maintain a stable, lunar-synchronous position: the earth-moon lagrange points  and .  is 56,000 km away from the earth-facing side of the moon, (at the lunar equator) and  is 67,000 km from the center of the moon's far side, in the exact opposite direction. at these points, the effect of the moon's gravity and the effect of the centrifugal force resulting from the elevator system's synchronous, rigid body rotation cancel each other out. the gravitational stability of these lagrange points are not permanent, ( and  are in unstable equilibrium along a straight line between earth and moon,) but so long as small inertial adjustments are made to account for minor gravitational perturbations, any object positioned there can remain stationary. both of these positions are substantially farther up than the 36,000&am
Exploration_of_the_Moon Space_elevator