How close are we to long-term human habitation beyond low-Earth orbit? Colonies on the moon or Mars are still many years off, but the good news is there are several serious efforts underway to make it happen.
The ISS. The closest thing we currently have to a space colony is the International Space Station. While it can be considered a success in terms of international cooperation and scientific research, the ISS far from self-sufficient. Sweat and urine can be recycled into fresh water and filters and scrubbers keep the air breathable, but without regular resupply missions, the station's occupants wouldn't last long. Still, the future looks bright up there – NASA has several ISS missions scheduled for 2010, expanding the station and adding new components (as well as spare parts).
Lunar Colonization. The best prospect for a human colony on the moon seems to be NASA's Constellation project. The Altair Lunar lander will be able to carry a crew of four astronauts to the moon and support them there for a seven-day mission. Alternately, it can descend robotically to the moon carrying critical infrastructure for a longer-term lunar outpost. When completed, that outpost will support a crew of four for up to 180 days. NASA has a slick interactive website that explains Constellation.
A great deal of thought is being put into what astronauts will live in on the moon. The first moon base will likely be an inflatable dome. NASA has been testing such a design at McMurdo Station in Antarctica to see how it deals with extreme cold. Although there are no blizzards on the moon, the test will also prove whether or not the "lunar bounce house" is tough enough for a long-term mission. An inflatable habitat has the advantages of being light-weight and only requiring a few hours to set up.
Beyond that preliminary outpost, lunar settlers will require something a bit more sturdy and permanent. Rigid, durable building materials are too heavy to send from the Earth's surface to the moon – it would be impossibly expensive. The best option, then, is to create building supplies from the raw materials already present on the moon. The recent discovery of a large amount of water on the moon makes the production of concrete using lunar regolith much more feasible, but even without water, it's possible. In 2007, a paper published in the Journal of Aerospace Engineering explained how the regolith could be processed into sulfur, which could then be mixed with regolith to make waterless concrete. They even examined the physical properties of said concrete, and proposed a cylindrical habitat structure.
A more recent paper in the same journal studied potential lunar colonization in-depth, examining potential structural designs, insulation, power needs and other factors. If you're not willing to take the researchers' word for it, you could always study space architecture yourself. The University of Houston College of Architecture boats the Sasakawa International Center for Space Architecture (SICSAl). Students design and model space vehicles, orbital stations, and lunar and Martian habitats. Many of their designs come directly from NASA requests. While fun, it is a challenging curriculum, since designers must incorporate radiation shielding and variations in gravity, problems terrestrial architects rarely have to consider.
Martian Colony. We're a long way from colonizing Mars – decades, at least. However, NASA's Constellation program does have a Martian outpost as its ultimate goal. Creating a colony on the moon will generate an enormous amount of data that will directly aid the quest to put humans on Mars.
The European Space Agency isn't waiting around, though. They're currently screening volunteers to take part in a 520-day simulated mission to Mars. This year, they wrapped up a 105-day precursor simulation. The long-term test will examine the physical and psychological effects of such a mission.
Candidates should be aged 20-50, motivated, in good health and no taller than 185 cm. They should speak one of the working languages: English and Russian. Candidates must have a background and work experience in medicine, biology, life support systems engineering, computer engineering, electronic engineering or mechanical engineering.
Beyond. The "moon to Mars" path for human colonization of space isn't the only idea out there. In 2008, a group of researchers proposed a "company town" model for creating a space mining colony. What would they be mining? Water. Where would they be mining it? From the inside of comet 4015 Wilson-Harrington. Sometimes considered an asteroid, 4015 may in fact be a burned-out or intermittently active comet. The researchers believe that finding a large supply of water somewhere other than Earth is the key to post-Earth survival of the human race. Their company town model proposes an entire economic system that would support up to 10,000 colonists.
Image: NASA Ames Research Center