Boeing 747 variants served as key assets in NASA's shuttle program

NASA modified two Boeing 747 Jumbo jets to serve as Space Shuttle Carrier Aircraft, which are now retired and on display. These aircraft were equipped with extra stabilizers on the tail and struts on top for attaching orbiters. NASA selected the Boeing 747 in the 1970s, using an American Airlines Boeing 747-100 and a Japan Air Lines Boeing 747-100SR. Both aircraft were identical in performance after modifications.

The first test flights with these carriers took place in 1977 with the shuttle Enterprise, which was released during flight to glide back down. The carriers transported space shuttles from landing sites to the Kennedy Space Center and other locations too far for ground transport. "The orbiters were placed atop the SCAs by Mate-Demate Devices," according to NASA.

NASA 905, purchased from American Airlines in 1974, was the first carrier used until November 1990 when NASA acquired NASA 911 from Japan Air Lines. "NASA 905...was the first and only SCA used by the space shuttle program until November 1990," stated NASA. After retiring, NASA 905 delivered Discovery, Enterprise, and Endeavour shuttles to museums across the country.