Cape Canaveral, Florida US - The vertical stabilizer of space shuttle Atlantis emerges from Orbiter Processing Facility One on the morning of Tuesday, May 17, 2011. Atlantis is scheduled to fly the final mission of the space shuttle program in early July of 2011.

Cape Canaveral, Florida US - Space shuttle Endevour hangs inside the Vehicle Assembly Building in preparation for mating with the external tank and solid rocket booster stack.

Cape Canaveral, Florida US - Space shuttle Endevour hangs inside the Vehicle Assembly Building in preparation for mating with the external tank and solid rocket booster stack.

Cape Canaveral, Florida US - Space Shuttle Endeavour departs the VAB for her final journey to Pad 39A on Thursday, March 10, 2011. STS-134 is scheduled to launch on April 19, 2011.

Cape Canaveral, Florida US - Space shuttle Endeavour sits on pad 39A at NASA's Kennedy Space Center in Florida after the Retractible Service Structure was rolled back just after midnight on, April 29, 2011.

Space Shuttle Discovery sits on Pad 39A after roll-back of the retractable service structure on the evening of February 23, 2011. Discovery is set to lift-off around 4:50 p.m. EST on February 24, 2011 to deliver the Italian-built Permanent Multipurpose Module and Express Logistics Carrier 4 to the International Space Station.

Space Shuttle Endeavour sits on Pad 39A on Friday, March 11, 2011. Endeavour is scheduled to launch on April 19, 2011.

Cape Canaveral, Florida US - Commander Mark Kelly (right) gives a thumbs-up before he and his crew depart the Operations and Checkout Building for the pad on April 29, 2011. Endeavour's final flight was delayed until Monday, May 2, 2011 at the earliest after technical issues led to a scrub as the crew was on their way to the pad.

Space shuttle Discovery blasts off from Pad 39A bound for the International Space Station on Thursday afternoon February 24, 2011. Discovery will deliver the Italian-built Permanent Multipurpose Module and Express Logistics Carrier 4 to the International Space Station.

Space shuttle Discovery blasts off from Pad 39A bound for the International Space Station on Thursday afternoon February 24, 2011. STS-133 will deliver the Italian-built Permanent Multipurpose Module and Express Logistics Carrier 4 to the International Space Station.

Cape Canaveral, Florida US - Space shuttle Atlantis lifts off from Pad 39A on Friday, July 8, 2011. Atlantis is embarking on her 33rd flight and the 135th and final flight of the Space Shuttle Program and will deliver the Rafaello Multi-purpose Logistics Module and Lightweight Multi-Purpose Carrier to the International Space Station.

Cape Canaveral, Florida US - MV Liberty Star sits in Canaveral Lock with the first of space shuttle Atlantis's two solid rocket boosters as onlookers take pictures on Sunday, July 10, 2011.

Cape Canaveral, Florida US - Space shuttle Discovery lands on runway 15 at the Shuttle Landing Facility at Kennedy Space Center in Florida on Wednesday, March 9, 2011.

Cape Canaveral, Florida US - Space shuttle Atlantis lands on runway 16 at the Shuttle Landing Facility at the Kennedy Space Center in the early morning hours of July 21, 2011. Atlantis has logged 307 days in space and almost 126 million miles during her 33 flights.

Cape Canaveral, Florida US - Space shuttle Discovery sits inside Orbiter Processing Facility Two at the Kennedy Space Center after completing her final flight on Wednesday, March 9, 2011.