Gardner died in Colorado Springs, according to his obituary in the Colorado Springs Gazette. The obituary did not list the cause of death. The NASA website says he died on Feb. 19.
Gardner flew two shuttle missions, in 1983 and 1984. He logged 337 hours in space and 225 Earth orbits, and he went on two spacewalks totalling 12 hours.
The 1983 mission, in the Challenger, was the first night launch and first night re-entry for the shuttle program. The 1984 mission salvaged two satellites that were stuck in the wrong orbits and brought them back to Earth. After Gardner helped retrieve one of them, a Western Union communications satellite, he posed for a photo outside the shuttle with a "for sale" sign.
A commander in the Navy, Gardner then returned to active duty. He served as the US Space Command's deputy director for space control at Peterson Air Force Base in Colorado Springs.
He retired from the Navy in 1990 and worked for TRW Inc, Northrup Grumman and the National Renewable Energy Laboratory in Golden, Colo. He retired from civilian work in January 2013.