[elihu]

I haven't read the book and maybe the argument is solid, but I'm inclined to disagree. For mining, maybe Mars isn't the best place (hoisting stuff out of the gravity well might not be worth it except for high-value metals), but on the other hand it has decent gravity and an atmosphere, which means it's more suitable for human habitation and fuel processing than the asteroids. And living on a planet has a certain appeal that living on a ship doesn't.

In the far future we might have better habitats in the asteroid belt than on Mars, but that's pretty far out. In the medium term, I expect Mars will be an important fuel stop at the least.

I guess there'd be a kind of a self-perpetuating economic force at work: mining would be most lucrative when the products can be consumed near where they're made, and if there's a heavy demand for construction in the asteroid belts then the asteroid belts are where most of the materials will come from. If it's on Mars, then the materials will be gotten on Mars. (That's assuming that material shipment is expensive. On the other hand, if you can mine iron in the belts and then just lob it at Mars with a rail gun and have the Martians drive out in rovers to collect the splatters of molten metal off the surface, then maybe the economics of non-local mining can work out.)

[blkhawk]

Mars might not be worth the effort if you have good asteroid mining - you could say build a O'Neil type cylinders inside an asteroid from local resources and spin them up. Some of the Tech you need for mining might transfer directly into tech or building structures like this. For instance refining metals in zero-G via rotating smelters to separate materials might serve as system to spin up and control the cylinder rotation.

You might even get most of the stuff aside from metals as byproducts of the metal refining process (water, oxygen(from oxids) and carbon mostly). Nitrogen and Phosphor might need importing.

Most of the leftover asteroid serves as Protection against small collisions.

[elihu]

If water/oxygen/carbon are readily available, I guess that would go a long ways towards making asteroids self-sufficient. On the other hand, if they're available but one can only extract a small amount at a time as a byproduct of mining, then Mars might still be pretty attractive where those things are available in inexhaustible quantities with low effort.

I'm assuming that huge amounts of methane (or other suitable fuel) and oxygen will be wanted for propellant, though maybe ion propulsion makes that less essential.