Gardner first flew in space as pilot on the crew of STS-27, aboard the Space Shuttle Atlantis, on December 2–6, 1988. The mission carried a Department of Defense payload and is noteworthy due to the severe damage Atlantis sustained to its critical heat-resistant tiles during ascent. Gardner next flew as pilot on the crew of STS-35, aboard the Space Shuttle Columbia, on December 2–10, 1990. The mission carried the ASTRO-1 astronomy laboratory consisting of three ultraviolet telescopes and one x-ray telescope.