How frequent are stellar collisions, anyway? I'd say pretty damn rare because I haven't read about them much.
(In Dragon's Egg, I am sure you know the book, a neutron star passes near our Solar System. Not close enough to cause any major trouble, but the orbits of the outer planets get slightly perturbed. Which gets me thinking - all it would take to end us is a reasonable close stellar fly-by by a near Sol-mass star. It would either scatter the planets or wreak havoc with their orbits. It would be less Hollywoodish in appearance, but just as deadly for the human race/life on Earth in general. We would also be totally powerless against that.)
I believe it would have to be a bit more than 'reasonably close' to really mess up the solar system. As in, within the Oort cloud, I think. Further out than that, it likely wouldn't do much to us, assuming it's Sol-mass or less. There could actually be brown dwarfs dancing all around us that we don't know about because the effect is so tiny and they are so dark.
Of course, this could be what you meant by 'reasonably close'.
Well, OK. But this looks hardly likely to pay off in anything like the next 100 years. I can see that getting your materials in space for use in space makes a lot of sense in theory. But you'd need to set up a whole processing system up there in order to exploit this material. My mind just boggles with the difficulty of all this.
I can see increasing use of nanotechnology making the cost of getting technologies out into space much much cheaper using existing propulsion techniques on Earth. Getting people into space seems a much less saner approach, and I don't see how you could realistically expect to carry out significant mining and manufacturing without the presence of human beings.
Still, there you go. Nothing to be lost by looking into it, properly.
Space Mining is going to be heavily automated for reasons of cost and simplicity. We are fast approaching the point where automated systems could do this job as well as a human could, once we have figured out 'how' to do it in the first place. It just wouldn't make sense to send out a lot of humans to do the job if it can be avoided. Bots are cheaper and safer by huge margins. Of course, this doesn't mean there won't be any humans out there wildcatting it up.
I'd also like to address the 'why' part from the previous page.
Yes, nickel and iron are abundant. But look at the toll mining takes on the environment, look at how expensive it is for a given amount of ore.
On an asteroid, no one cares if you pollute it or completely wreck it. There are no otters and seals and bald eagles to worry about. Plus, there is an insanely large amount of ores to be had relatively easily (once you are actually there and doing it - start up costs will be enormous) compared to Earth veins.
Then there are those precious metals and rare-earths. I've said this before several times, but it's worth repeating:
Think of all the electronics that use things like gold and molybdenum and are expensive as a result. Or all the electonics that use cheaper substitutes to keep prices down but are therefore inferior. Access to an asteroid will crash the market for these metals - and that's a great thing. Suddenly, we will find new uses for these rare materials and the goods we have will be cheaper. Plus, you won't have to worry as much about the impact on the environment that your new iPad cost because it's materials came from the void.
Remember, at one point, aluminum was considered more precious than all the other precious metals. Imagine a world where it still was, now imagine a world where all of the precious and rare earths were no longer precious or rare.
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