Margaret Rhea Seddon, American physician and astronaut
Margaret Rhea Seddon (born November 8, 1947) is an American surgeon and retired NASA astronaut. After being selected as part of the first group of astronauts to include women in 1978, she flew on three Space Shuttle flights: as mission specialist on STS-51-D and STS-40, and as payload commander for STS-58, accumulating over 722 hours in space.

A graduate of the University of California, Berkeley, and the University of Tennessee College of Medicine, Seddon was awarded her doctor of medicine (MD) degree in 1973. She did her internship at the Baptist Memorial Hospital-Memphis three years residency at the University of Tennessee hospitals in Memphis, where she was the only woman in the General Surgery Residency Program. Before, during and after her career in the astronaut program, she has been active in emergency departments in Tennessee, Mississippi and Texas.

Selected as an astronaut candidate by NASA in January 1978, Seddon became an astronaut in August 1979. During the STS-51-D mission in April 1985, she used her surgical skills to operate a bone saw to help build homemade repair tools for a U. S. Navy Syncom IV-3 satellite.The STS-40 Spacelab Life Sciences (SLS-1) mission in June 1991 was a dedicated space and life sciences mission, during which the crew performed experiments which explored how humans, animals and cells respond to microgravity and re-adapt to Earth's gravity on return. Other payloads included experiments designed to investigate materials science, plant biology and cosmic radiation, and tests of hardware proposed for the Space Station Freedom Health Maintenance Facility. For the STS-58 Spacelab Life Sciences-2 (SLS-2) mission, Seddon was the Payload Commander. During the fourteen-day flight in October and November 1993 the crew performed neurovestibular, cardiovascular, cardiopulmonary, metabolic, and musculoskeletal medical experiments on themselves and 48 rats, expanding our knowledge of human and animal physiology both on earth and in space flight. In addition, the crew performed ten engineering tests aboard the Space Shuttle Columbia and nine Extended Duration Orbiter Medical Project experiments.Her work at NASA also included development of the Space Shuttle Orbiter and payload software, the Shuttle Avionics Integration Laboratory, Flight Data File, Shuttle medical kit and checklists for launch and landing. She was a rescue helicopter physician for the early Shuttle flights and support crew member for STS-6. She served on NASA's Aerospace Medical Advisory Committee, as Technical Assistant to the Director of Flight Crew Operations, and as a Capsule Communicator (CAPCOM) in the Mission Control Center. In September 1996, she was detailed by NASA to Vanderbilt University Medical School in Nashville, Tennessee. She assisted in the preparation of cardiovascular experiments that flew aboard Space Shuttle Columbia on the Neurolab Spacelab flight in April 1998. Seddon retired from NASA in November 1997. She subsequently became Chief Medical Officer of the Vanderbilt Medical Group.