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I thought it was a good question - somebody else ask it if you like.

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    – L.Dutch
    Nov 6 '18 at 6:16
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There is plenty of solar energy in the asteroid belt, and that would be my answer for the abundance and variety of asteroids to be found there.

As an answer to Could you liquefy an asteroid to collect its resources?, I provide most of an asteroid mining operation, including power. With a 100 meter diameter parabolic mirror made of paper-thin polished aluminum, near the center of the asteroid belt (400M km) you can capture about 1.5 Mw of solar energy (190 watts per square meter; vs 1370 watts per square meter anywhere near Earth). That size mirror is manageable in space, and you can have hundreds or thousands of them working together. They can power Stirling heat engines, or even closed cycle steam engines, to turn the heat into electricity. Or they can be used to focus light to any degree on photovoltaics which generate electricity more directly. Or to provide enough heat to melt the asteroid material so it can be centrifuged at very high centrifugal gravities to separate it into rings of constituent masses.

Any mining or manufacturing operation in space is going to have accidents and problems, the further from Earth the better. Every "planetary" surface like a moon is going to have a gravity well to deal with, which complicates everything. The place to mine is in microgravity, where things are easier to move and you can command and position in all three dimensions without difficulty, and generate all the gravity you DO need by centrifugal force, with the precise amount of gravity you want.

That includes within a miner's habitat, which can include a hospital, game rooms, exercise fields, spacious quarters, whatever is desired.

One primary extraction from asteroids is going to be iron for construction steel. The miner's habitat can be large, because in space the steel is cheap. I imagine it would the first thing they start building. Steel produced on Earth (or in any gravity well) is extremely expensive to lift out, that's why our ISS can't be the size of a town with foot-thick steel walls. If it is produced in space it can be "shipped" hundreds of millions of kilometers with very little fuel, just a shove in the right direction, and deceleration.

On the economic side, the raw materials and energy to produce the steel and power the robots that do most of the work are free, mining would be a profitable operation, and considering the price of alternative steel, the profit margins do not have to be modest. Plus, of course, the miner's will find trace levels of other valuable metals.

From This Link:

An asteroid’s composition is mainly determined by how close it is to the Sun. The asteroids that are nearest the Sun are mostly made of carbon, with smaller amounts of nitrogen, hydrogen and oxygen, while the ones further away are made up of silicate rock. Silicates are very common on Earth and in the Solar System. They are made up of oxygen and silicon, the number one and number two most abundant elements in the Earth’s crust. The metallic asteroids are composed of up to 80% iron and 20% a mixture of nickel, iridium, palladium, platinum, gold, magnesium and other precious metals such as osmium, ruthenium and rhodium. There are a few that are made up of half silicate and half metallic.

As I detail in my other answer, even the gases (hydrogen and oxygen being of particular interest) can be captured from the asteroids by the miners.

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Earth Orbit

The first step in conquering space is simply to escape the tyranny of the Earth's gravity well. The delta-v from Earth's surface to LEO (as in the ISS) is around 9.4 km/s. Meanwhile, the delta-v from the Moon's surface to LEO is more like 2.7 km/s. Once you get off of Earth, it is a lot cheaper to get resources from anywhere. Here are a list of benefits for having a large colony / spaceport in LEO.

  • Cheapest trade with Earth: If the spacers eventually want to trade with Earth, LEO is the place to do it. The cheapest possible launch with a chemical rocket is to blast into LEO. Once there, you can transfer cargo to more efficient ion drive spacecraft to take it anywhere else. Alternately, sub-orbital launches and a skyhook might be the cheapest long term way to get thing off the planet. As far as putting things onto the planet, it is a relatively easy matter to de-orbit things from LEO using atmospheric drag.

  • Accessible materials: First, materials from the moon are very accessible from LEO. Moon to LLO (low lunar orbit) is about 1.9 km/s; but Moon to LEO is only 2.7 km/s, so its not much harder to get things to LEO than LLO. There are plentiful near-Earth objects that could be mined for materials. There is at least one confirmed trojan in Earth's L4 point, only 0.8 km/s away. There are several more objects in horseshoe libration, quasi-co-orbital solar satellites, and temporary satellites. For example, 2006 RH$_{120}$ is a near Earth asteroid that orbited the Earth from 2006-2007, before it went back to orbiting the sun. Every 20 years or so, it could be 'captured' but a little (nuclear explosive?) nudging and put into Earth's orbit.

  • Plentiful sunlight: Or, at least, as much sunlight as they have here on Earth. Earth orbit also has the advantage of little time with no light; lunar eclipses are rare and even an equatorial orbit gives you >12 hours of sunlight every day. That is certainly enough from plant life evolved on Earth.

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