Basic Information: http://en.wikipedia.org/wiki/Rotating_wheel_space_station
Extra Information: Space Colony 001 was built 20 years ago as a stepping stone for early space craft that could not make it all the way to the Moon in one trip. It is the Earth's oldest space habitat, and the largest concentration of people in one place in space with a population of nearly 10 million people. It is also a very popular tourist spot for those who can not afford a trip to a private space suite or the Moon.
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