Margaret Rhea Seddon is an American surgeon and retired NASA astronaut. She was selected as part of the first group of astronauts to include women in 1978. Dr. Seddon spent 19 years with the National Aeronautics and Space Administration (NASA). She served as a Mission Specialist on Space Shuttle flights in 1985 and 1991 and as Payload Commander in charge of all science activities on her final flight in 1993. This brought her total time in space to 30 days.