But Mir has been vacant since the last crew departed in June, and the aging outpost may never be occupied again. The United States hasn't had a full-time presence in orbit since the last crew left Skylab in 1974. The first crew members of the new station, like many space enthusiasts on the ground, regard the crossing of this threshold as the beginning of a more sustained and systematic planetwide approach to research in weightlessness and preparation for eventual human expansion into space. This time, they say, they're moving in for good. They will be living in a busy construction site as the nascent station continues to be built around them, even as its humming systems keep them alive.
Every single item has to be tied down in some way to keep it from floating off.
They may often find themselves with too many things in their hands and no way to put them down. A person, working with a visual system that evolved in gravity, is not accustomed to seeing pliers or a wrench floating one foot in front of his or her eyes. But veterans learn to maneuver like fish. They may have difficulty sleeping because of the sheer excitement of being up there, the noise levels in the close confines, and the absence of normal day-night cycles. As the space station whips around the planet 16 times a day, the sun rises and sets every 90 minutes.