Grabe became a NASA astronaut in August 1981. He served as a chief verification pilot for (Space Transportation System) STS-3 and STS-4 entry guidance, navigation and control simulation testing; as the Deputy Manager for Operations Integration, Space Shuttle Program Office; and subsequently as the Chief of Training within the Astronaut Office. A veteran of four space flights, Grabe served as pilot on STS 51-J (October 3-7, 1985) and STS-30 (May 4-8, 1989), and was the mission commander on STS-42 (January 22-30, 1992) and STS-57 (June 21 to July 1, 1993).