Margaret Rhea Seddon (born November 8, 1947) is a physician and retired NASA astronaut. After being selected as part of the first group of astronauts to include women, she flew on three Space Shuttle flights: as mission specialist for STS-51-D and STS-40, and as payload commander for STS-58. Both before and after her career in the astronaut program, she has been active in the medical community in Tennessee, Mississippi and Texas.