It's time for this old anarchist to play devil's advocate again, so don't be too harsh on me, OK?

I too, am a space enthusiast, trained in the sciences and employed in high technology all of my life,and a voracious reader (at one time, anyway) of science fiction. But let's look at the evidence for the potential for space colonization. Sure, we have the technology to send probes anywhere in the solar system, and if we could generate the political will I have no doubt that by the end of this century we will not only have the means of sending manned expeditions to any place in the solar system but perhaps even to maintain permanent bases anywhere we needed to. All that is lacking is the money, and with a little luck, we'll find something out there that will make it worth our while to go, or even stay.

If we use our own planet as a model, we have been able to permanently occupy every hostile environment on the earth's land surface, and I don't doubt we could operate permanent bases on the ocean floor if we chose to do so. If we need to, we can move into the Australian Outback, polar regions, Arabian desert, Siberian Tundra, Amazon rain forest, Himalayas, the mid-Pacific basin and even near-earth orbit. We simply show up and set up shop, ship in everything we need, and use our technolgy to continue to supply our outpost. The problem in space is different in degree only, not in kind.

But occupation is not the same as colonization. I would define a colony as a settlement capable of being self-supporting, at least for the most part. Its contact with the home world would be limited, and it would have to be firmly established enough that it was capable of long, perhaps indefinite periods of isolation. Some might even argue that the ability to exploit local resources and ship valuable commodities back would also be a requirement, but I'll be generous and waive that and assume the earth would graciously grubstake our settlements on speculation. We are not capable of doing this now in any of those places I mentioned in the previous paragraph, even though stone age peoples were able to do this readily thousands of years ago. The Inuit weren't just capable of visiting the Arctic, they earned a living there. The same can be said for the islands of the Pacific, where Neolithic man was not only able to survive, but navigate his canoes at will. We can't do it without ships, harbors, aircraft, landing strips, and lots and lots of fuel. Look at what it takes to get just a few hundred people through an Antarctic winter, and they're not sending back any gold or furs or tobacco.

The technology we have created that allows us to travel to and gain a foothold in these hostile environments is based on a world-wide system of engineering and finance that requires the resources of an entire planet and its people to operate. It is not portable. Every drop of lubricant, every ounce of fertilizer,
every watt of energy needed to supply an off-world colony would have to be brought in, or manufactured on site. So would the technology needed to make it. When the faceplate of your pressure suit cracks, or you need a ball bearing, you're going to have to replace it--from scratch, or order one from home. ISS may survive for years, but it is totally dependent on frequent supply, and we can barely do that now. And what about the human skills needed to manage this off-world maintenance industry? It may take us a century to learn how to grow crops on Mars, or to develop techniques to locate and mine chromium ore in the asteroid belt, and we won't learn how anywhere but there. Multiply that times everything you need to stay alive.

Assuming space travel some days becomes comparable in expense to ocean or air travel here on earth, we would still face the same problems establishing a permanent self-supporting base in space as we would say, in the middle of the Sahara. We couldn't do that today, and we can breath the air.