In sci-fi books and movies, colonizing other planets seems easy. All you have to do is make a jump to "hyper-space" in your star cruiser and -- voilà -- you punch through folded space-time and arrive at your destination instantly. In reality, we won't colonize space in great big leaps, but in a series of small steps, like living successfully in low-Earth orbit.
It's hard to imagine now, but in the heady days after Sputnik, scientists didn't know if humans could survive for long periods in space. The first flights into orbit carried animals, not astronauts, and it wasn't until 1961 that Yuri Gagarin rode a flaming rocket into space. Gagarin's historic flight lasted a mere 108 minutes, but it set the stage for longer missions.
By the mid-1970s, astronauts were living successfully in orbiting space stations. First came Skylab and Salyut, then Mir. On Mir, cosmonauts continued to break space endurance records. Musa Manarov and Vladimir Titov spent a year aboard the Soviet station in the late 1980s, but their achievement was eclipsed in 1995, when Valeri Polyakov completed a 438-day tour of duty.
Today, the International Space Station (ISS) stands as clear evidence that humans can live indefinitely in low-Earth orbit. Since the first crew arrived in 2000, the ISS has been continuously manned and has, through a variety of experiments, produced a vast body of knowledge about how to achieve self-sufficiency in space. In the coming decades, NASA and other international space programs hope to use that knowledge as a springboard to a destination beyond Earth's atmosphere.
From low-Earth orbit, it's just a hop, skip and jump to the moon (relatively speaking). We'll head there next.