NASA's Space Shuttle program was the United States government's manned launch vehicle program from 1981 to 2011. In 2012, Americans were witness to two incredible sights: Endeavor, inching down Los Angeles streets on a 160-wheeled carrier to its final destination, the California Science Center, and Discovery, flying over DC on the back of a jet on its way to the Smithsonian. Endeavor was the baby of the shuttle fleet, replacing Challenger, which exploded during liftoff in 1986, killing seven astronauts. Although Discovery and Endeavor hadn't flown in space since their final missions to the International Space Station, more than a year ago, the two ferry sightings this year were definitive as a signal that a 30-year era in spaceflight had come to an end. With the shuttles in retirement, private U.S. companies hope to pick up the slack, beginning with space station cargo and then, hopefully, astronauts.
Read more: Where are all the space shuttles now?