SCA

The Shuttle Carrier Aircraft is a modified Boeing 747-100SR that was built to transport Space Shuttle orbiters on its back. Two aircraft were configured for this role: N905NA and N911NA, both operated by NASA from the 1970s through 2012. The orbiter sat atop the 747's fuselage between the vertical stabilizer and the cockpit in a distinctive piggyback arrangement, held down by a custom structural interface.

The SCA carried an orbiter from the landing site back to the Kennedy Space Center or to maintenance facilities, a journey that took roughly 5 to 6 hours. The 747 itself carried fuel and support equipment but no internal cargo bay modifications; the shuttle simply rode mounted externally. This meant the combined aircraft weighed around 735,000 pounds at takeoff and flew at a reduced speed of approximately 450 knots, well below the 747's normal cruise speed.

The primary structural addition was a vertical tail cone mounted on top of the 747's fuselage to restore aerodynamic stability that would otherwise be lost with the orbiter perched above. Chase aircraft typically accompanied each ferry flight for visual monitoring. The arrangement required careful weight and balance calculation; the orbiter's center of gravity sat well above the 747's centerline, creating unusual handling characteristics that demanded pilots with specific training.

Not every landing site had infrastructure to support the SCA. When a shuttle landed in California at Edwards Air Force Base or at alternative sites, the SCA had to be positioned there first or the orbiter had to be transported by other means. The ferry flights were infrequent enough that scheduling them around maintenance and other NASA operations was a logistical puzzle.

The name distinguishes this aircraft sharply from all other 747s; there was never a commercial variant called the Shuttle Carrier Aircraft. Within the aerospace maintenance trades, the term is precise and singular. Both SCA aircraft were eventually retired and scrapped after the Space Shuttle program ended in 2011, so the term now carries historical weight in aviation documentation and archival records.