rrw4rusty said:
I'm writing a science fiction story and in the future we are having to bring iron asteroids down to Earth.
I read science fiction on occasion, but I toss the story if the basis is so ludicrous that I cannot suspend my disbelief. This falls into that category.
Why go after iron in space for the purpose of sending it down to Earth? Iron ore is cheap, cheap, cheap. Current prices of high grade iron ore are on the order of 10 cents per kilogram. Current cost of putting something into low Earth orbit is well in excess of $10,000 per kilogram, but with some promise that that might fall by a factor of 2 or 3. You are going to need to send fuel and equipment into space (lots of it) to go and retrieve those asteroids, mine them, etc. A five or six order of magnitude increase in the cost of iron or decrease in the cost of entry into space is needed to make asteroid mining for iron viable.
Sans a space elevator, sending stuff into space will remain very expensive for a long, long time. Use the iron in those asteroids up in space. Don't send it up from the Earth, but don't send it down to the Earth, either. You can collect your volatiles in space, too. You need to make the stuff that is sent up into space worth the cost of doing so. People, and maybe some equipment that just can't be manufactured in space. Similarly, you need to make the stuff that is sent back down to Earth worth the cost of doing so. Iron just won't cut it.
There are things that do cut it. Iridium costs over $10,000 per kilogram, for example. We
know that there are asteroids out there with a much greater relative abundance of iridium than occurs on the Earth: One such asteroid hit the Earth 65 million years ago. There have to be more of those out there.
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