Space Shuttle Endeavour mounted on NASA's Shuttle Carrier Aircraft, passes over the Golden Gate Bridge in San Francisco, Friday, Sept. 21, 2012. Endeavour is making a final trek across the country to the California Science Center in Los Angeles, where it will be permanently displayed. (AP Photo/Marcio Jose Sanchez)

The space shuttle Endeavour passes over the California state Capitol, Friday, Sept. 21, 2012, in Sacramento, Calif. Endeavour is making a final trek across the country to the California Science Center in Los Angeles, where it will be permanently displayed.(AP Photo/Rich Pedroncelli)

Space Shuttle Endeavour mounted on NASA's Shuttle Carrier Aircraft, passes over the Golden Gate Bridge in San Francisco, Friday, Sept. 21, 2012. Endeavour is making a final trek across the country to the California Science Center in Los Angeles, where it will be permanently displayed. (AP Photo/Marcio Jose Sanchez)

The space shuttle Endeavour passes over the California state Capitol, Friday, Sept. 21, 2012, in Sacramento, Calif. Endeavour is making a final trek across the country to the California Science Center in Los Angeles, where it will be permanently displayed.(AP Photo/Rich Pedroncelli)

In this photo provided by the Southwest Photo Bank, former U.S. Rep. Gabrielle Giffords and husband, former astronaut Mark Kelly, watch the Space Shuttle Endeavor fly over Tucson, Ariz. on its way to Los Angeles, Thursday, Sept. 20, 2012. Kelly, Endeavour's last commander, requested that the shuttle pass over Tucson to honor Giffords, who is recovering after suffering a head wound in a shooting rampage last year. (AP Photo/Southwest Photo Bank, P.K. Weis) MANDATORY CREDIT

The Space Shuttle Endeavour sits atop NASA's Shuttle Carrier Aircraft (SCA) at the NASA Dryden Flight Research Center at Edwards Air Force Base, Calif., Thursday, Sept. 20, 2012. Endeavour returned to its California roots after a wistful cross-country journey that paid homage to NASA workers and former Arizona Rep. Gabrielle Giffords and her astronaut husband. (AP Photo/Jae C. Hong)

The Space Shuttle Endeavour sits atop NASA's Shuttle Carrier Aircraft (SCA) at the NASA Dryden Flight Research Center at Edwards Air Force Base, Calif., Thursday, Sept. 20, 2012. Endeavour returned to its California roots after a wistful cross-country journey that paid homage to NASA workers and former Arizona Rep. Gabrielle Giffords and her astronaut husband. (AP Photo/Jae C. Hong)

Space Shuttle Endeavour mounted on NASA's Shuttle Carrier Aircraft, passes over the Golden Gate Bridge in San Francisco, Friday, Sept. 21, 2012. Endeavour is making a final trek across the country to the California Science Center in Los Angeles, where it will be permanently displayed. (AP Photo/Marcio Jose Sanchez)

Space Shuttle Endeavour mounted on NASA's Shuttle Carrier Aircraft, passes over the Golden Gate Bridge in San Francisco, Friday, Sept. 21, 2012. Endeavour is making a final trek across the country to the California Science Center in Los Angeles, where it will be permanently displayed. (AP Photo/Marcio Jose Sanchez)