Mark E. Kelly
A veteran of three spaceflights, his seat for this mission was pending after his wife, Congresswoman Gabrielle Giffords, was injured in a shooting. Thanks to her remarkable recovery and promising rehabilitation, he remained as Commander of STS-134.
His first trip into space was also with Endeavour, in 2001, and he has now logged 38 days in space. Kelly’s identical twin brother, Scott J. Kelly, has served as commander of Expedition 26 and worked with ESA astronaut Paolo Nespoli. The Kelly brothers are the only siblings to have flown in space.