In this image provided by NASA the NASA 747 Shuttle Carrier Aircraft with the space shuttle Discovery mated on top rolls into position for demating at Washington Dulles International Airport, Wednesday, April 17, 2012, in Sterling, VA. Discovery, the first orbiter retired from NASA's shuttle fleet, completed 39 missions, spent 365 days in space, orbited the Earth 5,830 times, and traveled 148,221,675 miles. NASA will transfer Discovery to the National Air and Space Museum to begin its new mission to commemorate past achievements in space and to educate and inspire future generations of explorers. (AP Photo/NASA, Bill Ingalls)