Jernigan studied physics, engineering science, astronomy, and space physics before NASA selected her with Astronaut Group 11 in 1985. Her scientific training made her a strong fit for Spacelab, observatory, and payload operations.

Her missions were STS-40, STS-52, STS-67, STS-80, and STS-96. They included life sciences, satellite deployment, ultraviolet astronomy, long-duration shuttle operations, and early ISS logistics.

On STS-96, Jernigan performed an EVA with Daniel Barry to outfit the young International Space Station. That spacewalk connected her earlier science-mission experience to the start of permanent station assembly.

After NASA, Jernigan worked at Lawrence Livermore National Laboratory.