Climbers ascend a ribbon, 100,000 km long, strung between an anchor on Earth and a counterweight in space. Connecting Earth and space in a way never before possible, the space elevator will enable us to inexpensively and completely expand our society into space.
Beyond Earth, space elevators on the moon and Mars open new economic opportunities and expand humanity's reach ever so slightly into the solar system.
More info: http://www.spaceelevator.com
NASA: http://science.nasa.gov/science-news/science-at-nasa/2000/ast07sep_1/