Mark Lee was selected as an astronaut candidate by NASA in May 1984. In June 1985, he completed a one-year training and evaluation program, qualifying him for assignment as a mission specialist on future Space Shuttle flight crews.
His technical responsibilities within the Astronaut Office included extravehicular activity (EVA), the Inertial Upper Stage, Spacelab and Space Station systems.
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Lee also served as a spacecraft communicator in the Mission Control Center , as Lead Astronaut Support Person at the Kennedy Space Center , Chief of Astronaut Appearances, Chief of the Astronaut Office Mission Development Branch, Chief of the EVA Robotics Branch, and Chief of the EVA Branch. He also worked Space Station assembly issues for the Astronaut Office.

In total, during his four space flights,
Lee traveled over 13 million miles going around the world 517 times and spending 33 days in orbit.
Source  - Wikipedia