After ascending to the rank of Colonel in the United States Air Force, this military test pilot worked for the National Aeronautics and Space Administration (NASA) as a Mission Specialist for the March, 2008 STS-123 flight of the Space Shuttle Endeavour. He also participated in a later Endeavour mission, STS-130.
After receiving degrees in mechanical engineering and physics from Washington University in St. Louis, he earned a doctorate from the California Institute of Technology.
He was the recipient of an Air Force Achievement Medal and two Air Force Commendation Medals.
He married Hawaiian-born oceanographer and fellow NASA astronaut K. Megan McArthur.
In 2012, he succeeded Peggy Whitson as Chief of the Astronaut Office at NASA.