Robert Louis Behnken (; born July 28, 1970 in St. Ann, Missouri) is a NASA astronaut, engineer, and former Chief of the Astronaut Office. Behnken holds a Ph.D in mechanical engineering and the rank of colonel in the U.S. Air Force, where he served before joining NASA in 2000. He flew aboard Space Shuttle missions STS-123 (2008) and STS-130 (2010) as a mission specialist, accumulating over 708 hours in space, including 55 hours of spacewalk time. He is married to fellow astronaut K. Megan McArthur.