He logged 140 days in space on five shuttle flights, including the May 1989 mission of Atlantis to deploy the Magellan spacecraft. He was also the cosmonaut-researcher for the Russian Mir 18 mission when he was launched from the Baikonur Cosmodrome in March 1995 for a 115-day flight that involved 28 experiments. Thagard was selected as an astronaut in 1978 and retired in 1996.