Artist's impression of a future manned base on the Moon. The domes at left are habitation and laboratory modules, where the astronauts may work in normal conditions. The long tube running across the frame is a mass driver. This is a long series of powerful electromagnets. A cargo projectile is loaded at right, and is accelerated by the electromagnets firing in sequence. The projectile achieves enough velocity for a direct flight back to Earth, where it may be captured in orbit or re- enter the atmosphere by itself. Such techniques could be used for cheap return of minerals or manufactured metals and drugs from the lunar colony.