She served as a member of NASA's Aerospace Medical Advisory Committee, as a technical assistant to the director of flight crew operations, and as a capsule communicator (CAPCOM) in the Mission Control Center.

In 1996 she was detailed by NASA to Vanderbilt University Medical School in Nashville, Tennessee, where she assisted in the preparation of cardiovascular experiments that flew on the STS-90 Neurolab Spacelab flight in April 1998.

[12] Women were not permitted in the surgery doctors' lounge there, so she had to wait between cases on a folding chair in the nurses' bathroom.

[13] On July 8, 1976, the National Aeronautics and Space Administration (NASA) issued a call for applications for pilot and mission specialist candidates.

Seddon was contacted by Jay F. Honeycutt from NASA and was asked to come to the Johnson Space Center (JSC) for a week of interviews and physical examinations, beginning August 29, 1977.

[20] A particularly difficult part of the curriculum for Seddon was SCUBA training, which was conducted in the pool at the Clear Lake Recreational Center.

[22] As an astronaut candidate, Seddon drew a civil service salary of about US$22,000 (equivalent to $103,000 in 2023), which was more than she made as a surgical resident.

She figured that her astronaut job took up only fifty to sixty hours a week, which left time to practice medicine.

Seddon worked there until it closed twelve years later, then moved to Spring Branch Hospital, where she remained until she left Houston.

They were married on May 30 in a ceremony at the First United Methodist Church in Murfreesboro, followed by a reception at the Stones River Country Club.

Seddon (who retained her maiden name) then resumed her role with search and rescue in preparation for the upcoming STS-2 mission.

A malfunction in the Syncom spacecraft resulted in the first unscheduled spacewalk, rendezvous, and proximity operations for the Space Shuttle in an attempt to activate the satellite using the Remote Manipulator System (RMS).

Seddon used her surgical skills to operate a bone saw to help build homemade repair tools for the satellite.

[38] She was able to manually engage the start lever with the RMS, but the launch sequence did not commence, and the satellite was left in low Earth orbit.

[43] While she waited for her Spacelab Life Sciences mission to be scheduled, she sought out a refresher program in emergency medicine.

The course cost several thousand dollars, which she could not afford, but she wrote to Vincent Markovchik, the head of the program, and he agreed to waive the fee.

[44] In 1988 Abbey offered her the chance of another flight in the meantime, but Seddon declined, as she was hoping to have another child, and felt that the SLS-1 mission needed someone to watch over it, even if its launch was years in the future.

[45] Seddon also began to think about acquiring some managerial experience and went to see Carolyn Huntoon, the head of the Space and Life Sciences Directorate at JSC, about a secondment to her area.

Under Puddy, the job no longer entailed being a personal pilot and driver, but Seddon still worked on a variety of tasks.

These included preparations for the STS-26 "Return to Flight" mission, and developing policies in cooperation with the Space and Life Sciences Directorate.

[46] She left the position when she had her second child, Edward Dann Gibson (named after her father), who was born in March 1989.

One crew member, Bob Phillips, was grounded with a minor medical condition and was replaced by Millie Hughes-Fulford.

Hopes that training could now proceed uninterrupted were soon dashed; Seddon was called upon to participate in the selection of NASA Astronaut Group 13 (who became known as the "Hairballs").

During the nine-day mission, the crew performed experiments that explored how humans, animals, and cells respond to microgravity and re-adapt to Earth's gravity on return.

Other experiments were designed to investigate materials science, plant biology and cosmic radiation, and tests of hardware proposed for the Space Station Freedom Health Maintenance Facility.

Surgery was required to insert screws to realign the bones, and she had to spend six weeks in a cast and another six in a walking boot.

NASA management ordered the Director of Flight Crew Operations, David Leestma, to modify the experiments to harvest organs without killing the test animals.

[66] Seddon became the Assistant to the Director of Flight Crew Operations for Shuttle/Mir Payloads, a new position, which involved travel to Russia.

She also assisted in the preparation of cardiovascular experiments that flew aboard Columbia on the STS-90 Neurolab Spacelab flight in April 1998.

[73][74][75] In 2017 she was named as one of the University of Tennessee Centennial Top 100 Alumni and was a co-recipient of the Great American leadership award along with Gibson.