The US space shuttle Discovery sits atop NASA's 747 shuttle carrier aircraft early April 16, 2012 as they are parked on the apron of the Shuttle Landing Facility at Kennedy Space Center, Florida. The 747 with Discovery aboard will be flown to Washington April 17 for display at the National Air and Space museum. AFP PHOTO/Bruce Weaver (Photo credit should read BRUCE WEAVER/AFP/Getty Images)