It has been called the world's greatest piggyback ride: a space shuttle, atop a Boeing 747 jet aircraft. But this is no ordinary 747, this is the Shuttle Carrier Aircraft...the SCA. This specially modified jumbo jet was not only a taxi service for the shuttle, but also helped in the development of the shuttle itself. In 30 years of flying, the majestic image of a spacecraft joined to the SCA, became a symbol of American invention and ingenuity.