I've been working on a textbook about Space Systems Engineering: http://en.wikibooks.org/wiki/S...
In section 4.9 I do the numbers for orbital mining: https://en.wikibooks.org/wiki/...
The first product of asteroid mining is likely to be rocket fuel. Some asteroids (the carbonaceous type) contain up to 20% water and carbon compounds. This can be processed to Oxygen + Hydrocarbons, which is a common high-thrust rocket fuel. The lifetime mass return ratio of an asteroid tug is ~350:1, and if 20% is usable fuel, then you gain 70:1 just on that one product. Extracting water and carbon compounds only requires kitchen oven level heat, which is easy to do by concentrating sunlight.
There are lots of other products we can potentially extract from asteroids, but that's the easiest and most useful, since most anything you do in space needs some fuel to get where you want to go.
Asteroids did have geological processes, just different ones. The "metallic" type come from protoplanets which melted internally from radioactive decay early in their history. The iron and iron-loving elements sank to the core because they are the densest. Later collisions broke up the protoplanets, exposing their cores. The metallics are a high percentage of iron, nickel, cobalt, and a few other elements. The "stony-irons" come from regions that didn't fully separate the core and rocky layers. They range from low to high percentage iron, with the remainder being rock.
The other process that happened is thermal. Depending how far from the Sun a given asteroid first formed, and later orbit history, certain compounds condensed or not, and then could be baked. Probably the most significant difference is due to the "frost line", the distance at which water ice can remain solid in a vacuum. It happens to be right in the middle of the Asteroid Belt, where Ceres is. Objects beyond that distance tend to have a lot of water. Anything closer tends to have little water, though it can contain "hydrated minerals", where the water is chemically bound.
We actually know quite a bit about the composition of asteroids. Nature delivers samples to Earth in the form of meteorites. We can compare the spectra of meteorites to those from asteroids we get through telescopes, and infer what they are made of. We have flown past or orbited several asteroids, most notably the Dawn mission to Vesta and now Ceres, two of the largest asteroids. Spacecraft carry a larger variety of instruments and can do a better job of telling what the asteroids are made of.
As far as materials processing, we can design machines based on meteorite samples, or simulated samples, since meteorites are rare and valuable. If the Asteroid Redirect Mission that NASA wants to do happens, we would have a sizable boulder to experiment with. After taking science samples, they could try various processing methods on an actual piece of asteroid rock, in zero-g. I don't think we can design serious production units without a a few rounds of trying it on a small scale. For that, we would need at least a small asteroid tug that fetches back chunks from different asteroid types, so we have enough raw materials to experiment on. Most known asteroids are too big to move whole. A 30 meter one is anywhere from 18,000 to 90,000 tons. So for early space mining, we are talking about scraping loose stuff off their surfaces, or grabbing boulders.
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