On his third flight, Nagel was Commander of STS-37, which launched into orbit on April 5, 1991, from Kennedy Space Center, Florida, and landed on April 11, 1991, at Edwards Air Force Base, California. During this mission, the crew aboard the Shuttle "Atlantis" deployed the Compton Gamma Ray Observatory for the purpose of exploring gamma ray sources throughout the universe. The crew and conducted the first scheduled space walk in more than five and one-half years, and the first successful unscheduled spacewalk to free a stuck antenna on the satellite.