Earth won't always be fit for occupation. We know that in two billion years or so, an expanding sun will boil away our oceans, leaving our home in the universe uninhabitable—unless, that is, we haven't already been wiped out by the Andromeda galaxy, which is on a multibillion-year collision course with our Milky Way. Moreover, at least a third of the thousand mile-wide asteroids that hurtle across our orbital path will eventually crash into us, at a rate of about one every 300,000 years.
Why?
Indeed, in 1989 a far smaller asteroid, the impact of which would still have been equivalent in force to 1,000 nuclear bombs, crossed our orbit just six hours after Earth had passed. A recent report by the Lifeboat Foundation, whose hundreds of researchers track a dozen different existential risks to humanity, likens that one-in-300,000 chance of a catastrophic strike to a game of Russian roulette: "If we keep pulling the trigger long enough we'll blow our head off, and there's no guarantee it won't be the next pull."
Earth won't always be fit for occupation. We know that in two billion years or so, an expanding sun will boil away our oceans, leaving our home in the universe uninhabitable—unless, that is, we haven't already been wiped out by the Andromeda galaxy, which is on a multibillion-year collision course with our Milky Way. Moreover, at least a third of the thousand mile-wide asteroids that hurtle across our orbital path will eventually crash into us, at a rate of about one every 300,000 years.
Where?
We have many options. The National Space Society, whose more than 12,000 members are committed to establishing settlements in space, suggests that we'll probably first go to a planet that has the resources to support life. After completing a $200-million study in 2000, NASA reported that a colony could be dug several feet beneath our own moon's surface or covered within an existing crater to protect residents from the constant bombardment of high-energy cosmic radiation, which can damage our DNA and lead to cancer. The NASA study envisions an onsite nuclear power plant, solar panel arrays, and various methods for extracting carbon, silicon, aluminum and other useful materials from the lunar surface. The National Space Society, in its own 2008 report "Roadmap to Space Settlement," also identifies the moon as the logical initial stop, citing the presence of life-sustaining ice there as a precursor to permanent lunar bases, hotels and even casinos.
How?
The first challenge is simply to escape the pull of Earth's own gravity. "If you can get your ship into orbit, you're halfway to anywhere," the writer Robert Heinlein said. The space shuttle flew at around $450 million a trip, and today sending unmanned payloads into orbit will still set you back about $12,000 a pound, with much of the cost coming from the fuel burned in those first hundred miles.
To clear this imposing initial hurdle, engineers have dreamed up many rocketless launch systems. At the height of the Cold War, the U.S. Navy, as part of its High Altitude Research Program, investigated the feasibility of using a giant cannon to blast payloads into orbit. Physicist Derek Tidman, meanwhile, envisions using a massive centrifuge, which he calls a "slingatron," to spin objects until they reach a velocity at which they can be flung out of our gravitational well. And many engineers have contemplated the enticing possibility of constructing a "space elevator" that rides up a 62,000-mile-long cable held aloft, like a spinning lasso, by centripetal force.
When?
Right now, most of the progress toward space settlement is being accomplished in the private sector. Last December, Elon Musk's SpaceX completed a successful test flight of a reusable capsule capable of carrying up to seven people, and the company has a contract with NASA to shuttle cargo to the International Space station at per-pound costs far below the current rate. Virgin Galactic, Space Adventures and other companies have begun offering flights into low Earth orbit and brief stays in space stations, and Bigelow Aerospace has plans to launch an inflatable "space hotel" by 2015.
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