Since before the dawn of the jet age, some people have dreamed of a permanent outpost for people outside of Earth's atmosphere.

The international space station -- a multinational effort involving the U.S., Russia, Japan, Canada and the European Space Agency -- currently orbits our planet as the largest structure in space, much larger than the former U.S. Skylab and Soviet Mir stations.

The first crew boarded the station in November 2002 -- two years after the first components were put in orbit -- and it has been occupied continuously since them, including by five space tourists launched by the Russian space agency.

It is staffed by a three-person crew, with the U.S. space shuttle delivering new members -- and bringing back outgoing members -- when it makes construction visits. More than 20 previous construction missions have gotten the station where it is today.

A list of future construction missions describes 15 more space shuttle flights to finish building the outpost. Those flights will be supplemented by unmanned flights from Russia, Europe and perhaps Japan.

One of the goals of those future missions is to expand the crew capacity to six people. When complete, it will have more than 42,000 cubic feet of usable space. As of December 2006, it was listed at 15,000 cubic feet.

It weighs more than 470,000 pounds.

At a speed of more than 17,000 mph, the station goes around the world almost 16 times a day.

In 1995, the European Space Agency reported that building and operating the space station will cost about $130 billion over 30 years.