AsterAnts

But the "machine tools" needed to put raw asteroidal material into usable forms will likely have significant mass. So using extraterrestrial materialscould significantly lower the cost of construction and operations in space if the tools are there, which would suggest a large operation, not on a few tons. Yes, it is an inevitability of this logic that use of space resources only makes sense above a certain scale of operations. I heard someone advocate useof lunar materials for construction of GEO communication satellites. As big a booster of use of lunar resources as I am, I still had to express the opinion that at this scale, such use would not be economical. If talking about giant GEO communication platforms a mile or so across with multiple antennas each around a city block in area, on the other hand... In debating this on Usenet, I've had some people say that the excessive costs of getting set up for refining and manufacturing in orbit are so huge that use of space materials is never going to cost less than lifting everything up from Earth. But I think this is going too far in the other direction. At some scale, there's a crossover point where lift cost savings pay for the space infrastructure needed. I expressed the idea thusly: Would use of space resources save you money on the first, prototype SPS? No. On the first half dozen? Perhaps not even then. On enough SPS to make a significant contribution to global energy needs? You bet. Would space resources save you money on building Alpha? Nonsense. On half a dozen space stations? No. On a Stanford Torus? Yes. But strangely enough, there was one guy who insisted it would be cheaper to build a Stanford Torus from Earth-launched materials than to set up the industrial infrastructure needed to build it from space resources.