STS-135 Atlantis, the 135th and final mission of the shuttle program, launched on this date in 2011. Fun fact: The launch countdown halted at T−31 seconds from a lack of an indication that the Gaseous Oxygen Vent Arm had retracted and latched, a problem that had never occurred before

STS-135 Atlantis, the 135th and final mission of the shuttle program, launched on this date in 2011. Fun fact: The launch countdown halted at T−31 seconds from a lack of an indication that the Gaseous Oxygen Vent Arm had retracted and latched, a problem that had never occurred before