The Moon-Earth momentum exchange provides an economical method of transporting large quantities of raw materials from the Earth and the Moon to low Earth orbit. The raw materials are processed into orbital greenhouses. Water and ammonia are transported from the Earth by a two stage light gas gun. Moon dust (regolith) is transported by a plastic gunsling and solar sails. Loops orbiting the Moon and the Earth transfer reusable cargo containers among the gun, gunsling, and sails. The loops do not contribute net orbital energy to the cargo, so powerful winches are not needed. For every 1 kg of Moon dust, 1 kg of water and ammonia is brought to the Earth loop. The momentum of raw materials brought from the Moon is balanced by the momentum of raw materials delivered from the Earth. No bibliography. The minimum mass is 1000 tons.
The idea of dropping raw materials from the Moon to the deep gravity well of the Earth is not new. Tethers in Space Handbook (W. A. Bacarat & C. L. Butner, Bantam Books 1986) describes various methods including towers and slings. These methods are not economical because they require at least one year to transport cargo equal their own mass. The Moon-Earth momentum exchange can transport its own mass in about two weeks.
Hydrogen and nitrogen are essential to life, and yet they are rare on the Moon. Both elements have to be transported from the Earth in a convenient form, e.g., frozen ammonia. The ammonia is dissolved in water, poured into the reusable container and frozen into a block of ice (clathrate hydrate). The loaded container is fired from the gun and enters the Earth loop tube which accelerates it to orbital velocity. Next, the container is emptied, picked up by the solar sail, slowed down by the Moon loop and dropped on the Moon surface near the mining site. When the solar sail approaches the Moon loop, its orbit has an opposite direction to the loop. The sail must then return to the Earth before it can reverse its direction and pick up a container loaded with Moon dust.
A mining settlement is erected on the Moon's equator. The settlement is inactive during the lunar night which lasts approximately two weeks. When it is active, its main task is loading the Moon dust into containers and launching them via a plastic gunsling. The gunsling is shielded by rocks from radiation and temperature extremes. A loop orbiting the Moon picks up the containers and releases them when the solar sails pass by. The solar sails then guide the containers to the Earth loop.
Most solar sails look like kites or balloons. Kites are difficult to erect in space, while balloons are being punctured by space junk and meteoroids. A more practical sail design is aluminum foil transported to space on a spool and bent into a C-shaped beam by rollers. The foil is 1 micrometer thick except for ribs which are about 100 micrometer thick. The foil is made by vaporizing aluminum on a water surface.