Selected by NASA in May 1984, Brown became an astronaut in June 1985, and qualified for assignment as a mission specialist on future Space Shuttle flight crews. In December 1985, he was assigned to the crew of STS-61-N, a Department of Defense mission which was subsequently canceled due to the "Challenger" disaster. During 1986 and 1987, he was an astronaut member of the solid rocket booster redesign team. In February 1988, Brown was assigned to a new flight crew. He flew on STS-28 (August 8–13, 1989), following which he served as astronaut member on the Space Station Freedom Program. He next flew on STS-48 (September 12–18, 1991). With the completion of his second mission, Brown had logged over 249 hours in space.