Selected by NASA in 1985, astronaut Jeffrey Gemar completed his training in 1986 and went on to serve in a variety of technical roles supporting the Space Shuttle Program, including flight software testing, mission control communications, and astronaut appearances. He flew three missions, logging over 580 hours in space. Gemar participated in STS-38 (1990), conducting Department of Defense operations, STS-48 (1991), which deployed the Upper Atmosphere Research Satellite and conducted key atmospheric studies, and STS-62 (1994), a microgravity science mission that included over 60 experiments across various scientific disciplines, including biotechnology, materials science, and human physiology.

After retiring from NASA, Gemar was detailed to the Office of the Under Secretary of Defense, where he led the National Security Space Master Plan Task Force. This task force was responsible for developing a long-term, integrated strategy for national security space programs.