The Space Shuttle prototype Enterprise flies free after being released from NASA's 747 Shuttle Carrier Aircraft (SCA) to begin a powerless glide flight back to NASA's Dryden Flight Research Center, Edwards, California, on its fourth of the five free flights in the Shuttle program's Approach and Landing Tests (ALT), 12 October 1977. The tests were carried out at Dryden to verify the aerodynamic and control characteristics of the orbiters in preperation for the first space mission with the orbiter Columbia in April 1981.