My comments were a response to a challenge in a small mailing list:
... be shipping nickle-iron down from orbit
(come on, the stuff is dirt cheap now!)
I wrote that there are two issues:
It is not so expensive to bring steel down. Presuming you have recovered it from an asteroid, and you have moderate manufacturing capabilities (something all the space mining endeavors presume), you can form some of your steel into large re-entry vehicles (500 or 1000 ft across, say), load the rest of the steel inside, and de-orbit the aerobodies over a stretch of ocean. Design the aerobodies so they splash down slowly enough - subsonic will do - and at a low enough angle, that the splashes don't sink nearby ships. Design the RVs to float. Send tug boats out to pull in your steel laden barges.
Assuming you have got your space operation going (a big assumption, admittedly), the transport costs will not be too different from those currently incurred transporting steel across the Pacific.
At a 10% rate of discount, the present value of that gigaton is $170 billion.
At a 30% rate of discount, the present value of that gigaton is $66 billion.
Either rate of discount, that is real money.
Note, however, that no investor will put up a $100 billion to acquire that gigaton if his or her hoped-for rate of return is 30% ... and a desire for 30% is not outrageous for this kind of investment.
I don't know the elasticity of demand for steel, but suppose I brought back 100 megatons per year over 10 years, and sold it at $300 per ton. At a 30% rate of discount the prevent value of that gigaton is $93 billion. Still not attractive to investors, but getting there.
The financial issue is in balancing how much to sell --- the more you sell the lower your price --- against how slowly you get your money back.
Of course, a real calculation not only takes into account the other materials you could bring back (a kiloton of gold, perhaps?), but also postulates a probability distribution for different prices (a 10% chance during year 8 a price is $500/ton; a 15% chance it is $225/ton). Also, you postulate the probabilities of finding differing amounts of the various materials, and the probabilities for the costs for recovering them (0.1% chance the re-entry vehicles cost a half what you expected; 80% chance they cost more; 10% chance one of them goes off course and squashes the Bank of America headquarters building).
But illustrative as my numbers are, I think they are within the ball park.
I guess that my real point is that to consider space industry nowadays, you have to think very big -- a gigaton of steel is no small amount, nor is $100 billion. The threshhold costs are very high. By contrast, the Spanish paid much less, proportionally to their resources, in funding Columbus' expedition across the Atlantic in 1492: it was the cost of losing three ships. I don't know for sure, but I suspect it was less costly than losing three contemporary American aircraft carriers would be for the US. Funding an asteroid mining operation is more like risking the loss of all the US carriers, or more.
Someone asked if I took into account the cost of mining and refining.
My response:
First, in vacuum and free-fall, you can build very large, light-weight mirrors -- much larger than in any environment with weight and storms.
Second, the presumption is that as part of your $100 billion investment, you build semi-automated (or, ideally, fully automated) machinery to build and operate your plant. Because of the vacuum and microgravity, refining and gross manufacturing may be much simpler than on earth.
Now, I agree, you might not be able to buy this capability for $100 billion. This is one of the reasons private investors are leary of this sort of thing.
They fear the project will fail, like the French attempt to dig a Panama Canal in the 1890s. (Incidentally, in that set of projects, the experts you had to hire to make it possible were the research doctors and the railroad engineers. These were not the experts traditional canal builders thought were most important when planning. Doctors so your crew did not die; railroaders so you could move megatons of dirt.)
As for the aerobodies, they would not be powered by other than gravity, and by a space tug that pushes them into an earth-intercept orbit, and by ocean tugs that later tow them to shore.
A more difficult question concerns the effect air braking would have on the atmostphere.
This may be a problem (I am assuming some ablation, which would put particles in the atmosphere; like the exhaust of jets, this might be dangerous. I doubt the heat output would be a problem, since a thunderstorm generates more heat).
Another question is whether governments will "let anyone aim a giant steel bullet at their cities if they can help it."
This depends on the military imbalance of power and on the judgements the potential victims make regarding the likelyhood that these potential weapons will be used against them.
Suppose a US steel company undertook the project; many would figure that if the US wanted to destroy part of a city, it would bomb the city in the usual way. On the other hand, suppose the current Iraqi government understook this project. Many would presume a military as well as economic goal.
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