More practical on the moon - as per decades-earlier mass-driver concepts, in order to get raw materials into earth-lunar orbit. See http://en.wikipedia.org/wiki

More practical on the moon - as per decades-earlier mass-driver concepts, in order to get raw materials into earth-lunar orbit. See http://en.wikipedia.org/wiki/Mass_Driver_1 http://en.wikipedia.org/wiki/Mass_Driver_1