The mining and processing of minerals on the Earth is costly, both in terms of economics and of pollution. Just think of the processes which are necessary to produce simple pig iron. Not only do the mines themselves create huge scars on the Earth, but the smelting and processing of the ores produces soot, fumes, and acid rain. As we exhaust the high-grade ores, it becomes necessary to expend even greater efforts to extract metals from low grade ores. In the case of some other metals, we are often dependent on supplies from politically unstable parts of the world. What we really need is an abundant source of minerals that could be processed without causing pollution, and that could be available to any country having the technological ability to obtain it. The Moon and the asteroids provide such a source.

    Since the Moon is so close to us, and since it has already been partially explored, it is probable that our exploration of space will begin there. The Moon can be reached in a few days. It is rather rich in aluminum and titanium, but it cannot really be said to contain high-grade ores of any other metals. There is an enormous amount of oxygen locked into the Moon's minerals, and this could be extracted using solar power. But the Moon is deficient in carbon and nitrogen, and, as far as we can tell, it contains no water at all. The asteroids have all of these materials in abundance.

    It is estimated that a kilometer-size, nickel-iron asteroid contains 7 billion tons of iron, 1 billion tons of nickel, and enough cobalt to supply the entire world for 3000 years. The total value at today's prices would be about five trillion dollars!

    It would be possible to set up a mining camp on an asteroid, extract the metals from the ores, and ship the metals back to Earth. However, it would probably be more economical to bring the entire asteroid into orbit around the Earth. An asteroid in Earth-orbit would always be accessible, and the crews working on the asteroid could be replaced and resupplied frequently. A mining station on a distant asteroid would have to be self-sufficient for a year or more, and would be much more difficult to reach.

    There are several ways in which an asteroid could be transported into an orbit around the Earth. The one thing that makes it possible is the availability of practically unlimited energy from the Sun. Solar electric cells, or solar boilers, could be used to power a variety of propulsion systems. Perhaps the most promising system would be to use an electro-magnetic 'mass driver' to expel pieces of the asteroid at high velocities. In other words, the asteroid would provide the fuel to propel itself. A mass driver is a device which accelerates specially-designed 'buckets' along a track at extremely high velocities. The mass driver is powered by electricity, and it works best in a vacuum. Mass drivers have already been built which achieve payload accelerations of 30g, (30 times the force of gravity on the Earth's surface). It has been proposed that mass drivers be built on the Moon's surface, and could fire buckets of minerals into space, for later collection and delivery to Earth. Mass drivers could also be used as rocket engines. A rocket works by expelling gases out of a nozzle at high velocity. The expulsion of the gases in one direction pushes the rocket away in the opposite direction. Placed on an asteroid, a mass driver would fire bits of the asteroid away, thus pushing the asteroid itself into a different orbit. The power for the mass driver would come from a thin solar panel which would have to have a diameter approximately equal to the diameter of the asteroid itself. About a quarter of the asteroid would be consumed as fuel.

    Another way to move an asteroid is with sails. Yes, sails! These sails would not be powered by wind. Indeed, they would require the total absence of air in order to function. The sails get their 'push' from sunlight.

    Another technique which would help guide the asteroid to Earth is called 'gravity assist'. This is the technique which propelled the Voyager space probes from Jupiter, to Saturn, to Uranus, to Neptune, and beyond. In gravity assist, one uses the gravity of a planet to change orbit of a passing body. It is sometimes called the 'slingshot effect'.

    Calculations have been made for several possible asteroid retieval missions. Typically, they involve close flybys of the Moon, the Earth, and sometimes Venus. The entire mission, from Earth launch to 'parking' the asteroid in Earth orbit, would take three to four years. The same solar panels that provide propulsive power for the asteroid retrieval would furnish the energy for mining the asteroid after arrival.

LINKS TO: L5 Society L5 refers to a Lagrange point in space where the society wants to build a space colony.