Coats commanded a seven-man crew on STS-39, an unclassified eight-day Department of Defense mission launched from the Kennedy Space Center, Florida on April 28, 1991. Crew members worked around the clock in two-shift operations during which they deployed, operated and retrieved the SPAS-II spacecraft, in addition to conducting various science experiments including research of both natural and induced phenomena in the Earth's atmosphere. After completing 134 orbits of the Earth, "Discovery" and her crew landed at the Kennedy Space Center, Florida on May 6, 1991. With the completion of his third mission, Coats has logged over 463 hours in space.