dietz%usc-cse%USC-ECL%SRI-NIC@sri-unix.UUCP (10/26/83)
The message about failed technologies is well taken. We should definitely look for technologies that are impossible on the ground but feasible in orbit. Asteroid mining was given as an example of a technology in direct competition with ground based industry, and therefore not likely to succeed. This is incorrect. No one has suggested that the asteroids are a near-term economical source of iron or other common elements for use on the ground. At the very most rare, high value siderophiles such as platinum could be returned to earth. The real use of asteroidal (or lunar) material is as raw material for building large space structures. In space the cost advantage of terrestrial materials is nullified. Any large industry in space will require mass for factories, power supplies, raw materials, etc. Once this mass becomes sufficiently large the use of extraterrestrial materials will become economical. Extraterrestrial mining is a "secondary" industry that will support primary space industries, such as zero-g material processing, high vacuum processes, solar power collection and so on. ET-mining will be economical (and perhaps necessary) should *any* of these industries become very large. An idea I heard of for space processing: depositing high purity silicon on large plastic sheets. On earth the very high vacuum required could not be maintained for economically reasonable deposition rates; space provides an essentially infinite pumping capacity and much higher vacuum. Perhaps much larger & cheaper photovoltaic cells can be made this way?