A modified Boeing 747 Shuttle Carrier Aircraft carrying the space shuttle Atlantis lands at Lackland Air Force Base's Kelly Field Annex, Texas, June 2 to refuel. The shuttle was on its way back to NASA's Kennedy Space Center in Florida. (U.S. Air Force photo/Alan Boedeker)

A modified Boeing 747 Shuttle Carrier Aircraft carrying the space shuttle Atlantis lands at Lackland Air Force Base's Kelly Field Annex, Texas, June 2 to refuel. The shuttle was on its way back to NASA's Kennedy Space Center in Florida. (U.S. Air Force photo/Alan Boedeker)

A modified Boeing 747 Shuttle Carrier Aircraft carrying the space shuttle Atlantis lands at Lackland Air Force Base's Kelly Field Annex, Texas, June 2 to refuel. The shuttle was on its way back to NASA's Kennedy Space Center in Florida. (U.S. Air Force photo/Alan Boedeker)

The space shuttle Atlantis sits atop a modified 747 after landing at Lackland Air Force Base's Kelly Field Annex, Texas, June 2. The shuttle was ferried from Edwards Air Force Base, Calif., back to Florida after a 13-day mission in space to repair and upgrade the Hubble Space Telescope. (U.S. Air Force photo/Alan Boedeker)