A NASA worker photographs the Space shuttle Atlantis as it rolls out of the Vehicle Assembly Building for launch pad 39A at the Kennedy Space Center in Cape Canaveral, Florida May 31, 2011. (REUTERS/Scott Audette)

Click our photo to see milestones of US-manned flights to space.

A NASA worker photographs the Space shuttle Atlantis as it rolls out of the Vehicle Assembly Building for launch pad 39A at the Kennedy Space Center in Cape Canaveral, Florida May 31, 2011. (REUTERS/Scott Audette)

Click our photo to see milestones of US-manned flights to space.