A lunar rotovator is a rotating tether system designed by Hans Moravec.

The basic idea is that the tether is in lunar orbit at say, 50km altitude, but the tether is more than 50 km long, and spins with a counterweight so that it touches the ground one or more times per orbit. The spin is arranged so that the tip just stops relative to the lunar surface and hence can be used to pick an object off the lunar surface and throw it into space- towards the earth.

This of course takes energy, which would tend to slow the tether, but this can be compensated for catching a similar mass from the earth and dropping it down to the moons surface. This means that it can be used as a transport system.

The main material necessary to build this device is simply Kevlar, it is believed to be well within the realms of current technology; no unobtainium is needed.