...if you can develop a purely Belt-centered economy, where both producers and markets can trade with each other with minimum contact with gravity well populations. But if that's the case, why should earth entrepreneurs invest in bootstrapping an economy where they won't get to market the product back home? Even with exotic future propulsion and life support tech, space travel and settlement are orders of magnitude more expensive than maritime trade.

Hohmann transfer orbits between bodies in the Belt are energy-cheap, but take an awfully long time. Bringing material for Belt exploration, exploitation and settlement up planetary gravity wells is very expensive, but bringing back the goods and resources of the Belt to the inner solar system is just as energy-expensive--you have to slow down when you get home.

Its conceivable, even desirable for the long-term survivability of the species, that a Belt economy and civilization will arise, pretty much independent of the large populations on earth. And I am convinced it will happen, providing we don't consume all our resources first in a lunatic race to sell each other cell phones, pizza and haircuts.

But why would button-down, bottom-line Terran stockholder-owned corporations (or even courageous, visionary, innovative entrepreneurs) want to risk investing in it? They are better off investing here, where the risks are less, and where they will pay off in their lifetimes.

It appears to me if humanity is really serious about colonizing the solar system, making a huge investment now for an even larger payoff a century or two down the line, its going to have be done by governments. Private businesses don't make investments that won't make a profit until all the stockholders have died of old age.

Admit it Tom. This is a job that, in the long term, will be done by governments. In the short term, private enterprise will get rich on the contract work. That's how its worked up to now, and its worked extremely well. Private enterprise alone would never have given us Hubble, Chandra, Fermi, Spitzer or Webb. In fact, it wouldn't even have given us Comsats, LandSats or GPS.