During medical school, Clark did active duty training with the Diving Medicine Department at the United States Navy Experimental Diving Unit in March 1987. After completing medical school, she underwent postgraduate medical education in pediatrics from 1987 to 1988 at the National Naval Medical Center. The following year she completed Navy undersea medical officer training at the Naval Undersea Medical Institute in Groton, Connecticut, and diving medical officer training at the Naval Diving and Salvage Training Center in Panama City, Florida. Clark was designated a Radiation Health Officer and Undersea Medical Officer. She was then assigned as the Submarine Squadron 14 Medical Department Head in Holy Loch, Scotland. During that assignment, she dove with Navy divers and Naval Special Warfare Unit Two SEALs, and performed many medical evacuations from US submarines. After two years of operational experience she was designated as a Naval Submarine Medical Officer and Diving Medical Officer.

She is survived by her husband, fellow NASA flight surgeon Dr. Jonathan Clark (who was part of an official NASA panel that prepared the final 400-page report about the Space Shuttle Columbia disaster), and son, Iain, who was born in 1996.

Selected by NASA in April 1996, Clark reported to the Johnson Space Center in Houston, Texas in August 1996. After completing two years of training and evaluation, she was qualified for flight assignment as a mission specialist. From July 1997 to August 2000 Clark worked in the Astronaut Office Payloads/Habitability Branch. Clark flew aboard STS-107, logging 15 days, 22 hours and 21 minutes in space.

STS-107 Columbia – The 16-day flight was a dedicated science and research mission. Working 24 hours a day, in two alternating shifts, the crew successfully conducted approximately 80 experiments. Clark’s bioscience experiments included gardening in space, as she discussed only days before her death in an interview with Milwaukee media near her Wisconsin hometown. The STS-107 mission ended abruptly on February 1, 2003, when Columbia disintegrated and her crew perished during re-entry, 16 minutes before scheduled landing.