dietz@SLB-DOLL.CSNET (Paul Dietz) (03/01/86)
The advantages of using lunar material in space for shielding, rocket fuel, structural metals, and so on are well known. The lack of atmosphere on the moon and its much shallower gravitational potential (5% as deep as Earth's) make lifting mass using mass drivers or rockets potentially much easier. Unfortunately, rockets must import (at least) hydrogen, and mass drivers are large, complex, require on-site maintenance and a large power supply. I suggest a brute force approach. A thermonuclear explosive detonated in the moon's regolith will propel large quantities of debris into space. For example, a 10 megaton bomb, if it transfers 10% of its energy to kinetic energy of escaping ejecta, can accelerate about 1 million tons of ejecta to lunar escape velocity. The actual quantity of ejecta expelled will depend on the size of the bomb, the density of the regolith and how deeply the bomb is buried. There are several problems. If the moon were the only body involved the debris would either escape completely or eventually return to the lunar surface. However, the sun and earth also affect the trajectories of the ejecta, so some pieces can end up in somewhat stable orbits. We must be able to collect the ejecta in a reasonably short time. Collisions between debris particles will cause dissipation; perhaps some can settle into a ring or into the L4 or L5 points. High collection efficiencies are not needed as long as the uncollected ejecta deorbits quickly (by hitting the moon or by being sent by the moon into solar orbit), because not much machinery is needed on the lunar surface. If orbited lunar soil is worth $5/lb even 1% collection efficiency yields about $100 million worth of material.