Writing in the Space Review, Stephen Ashworth complains that we're losing sight of the great potential for space colonies:

For example, the material published so far by the DARPA-NASA Ames 100-Year Starship Study ignores colonies in space, despite their obvious relevance, as does Lou Friedman’s report on their recent meeting (see “Fly me to the stars”, The Space Review, January 24, 2011). Joy Shaffer’s 2004 essay “Better Dreams” at Spacedaily.com, enthusiastically referenced by one Space Review commenter, explicitly excludes colonies in space: “there is no need to massively industrialize any place in the solar system beyond the elevator terminals and power stations at geosynchronous orbit”. Even the Tau Zero Foundation focuses on “the ultimate goal of reaching other habitable worlds”.

Ashworth makes the case that, while the Earth gave us a great start, it's time to move on:

The conclusion has to be drawn that, while a planet is a good place for life to get started using unconscious means that can evolve spontaneously from the chemical substrate, once life has reached the stage of industrial development, its further growth depends on the use of technology to construct artificial space colonies, which use the material resources of planetary systems at a much higher level of efficiency.

As is so often the case in these sorts of analyses, these speculations are predicated upon the assumption that we will colonize space as humans, and not as cyborgs or non-corporeal artificial intellects. Ashworth continues:

First, the project of sending humans to the stars is absolutely dependent upon prior large-scale space colonization. To begin with, the passengers on any interstellar mission will be devoting the rest of their lives to the voyage and the explorations at their destination: a return journey within a human lifetime is hardly conceivable (barring some magical new propulsion technology, and even that is hardly likely to come cheap).

This means that no crewed starship will be dispatched until the viability of a space habitat has been demonstrated for at least one complete human lifetime (including one or more reproductive cycles, unless the starship is conceived as a suicide mission). With space colonization in progress, spurred by general economic and population growth, such a demonstration will be a matter of course, and will be funded by the broader economy. Without it, the demonstration will be an expensive one-off project, and volunteers (together with their yet unborn offspring) will have to renounce all claim to a normal life.

Ugh.

Okay, here's what I say to this: This is a noble endaevor given (1) our current biological condition and (2) our critical need to get off planet before we're wiped out by an existential catastrophe. There's no harm done in figuring out how to create a biosphere in space for biological humans. In fact, a fully robust and operational space station might actually save our ass. I'm all for it.

But if the discussion is about longterm interstellar exploration and colonization, and that's what this is, let's get real and discuss our potential to venture out as a postbiological species. As NASA's Stephen J. Dick has stated, "Biologically based technological civilization...is a fleeting phenomenon limited to a few thousand years, and exists in the universe in the proportion of one thousand to one billion, so that only one in a million civilizations are biological."

In a post-biological future, machines are the dominant form of intelligence in the Universe. Talk of humans venturing out is just plain silly and short-sighted.