US astronaut. His three space shuttle fights include the March 1996 docking of Atlantis with the Russian space station Mir. His six-hour space walk during this mission was the first to be undertaken during the docking of a shuttle with a space station. He logged 665 hours in space, leaving NASA in 1997 to become the space station flight operations manager for the Boeing Defense and Space Group. Clifford was assigned to the Johnson Space Center in 1987 and selected as an astronaut in 1990.
Subjects: Astronomy and Astrophysics.