Selected as a NASA astronaut candidate in May 1984, Culbertson completed basic astronaut training in June 1985. Technical assignments since then included: member of the team that redesigned and tested the Space Shuttle nosewheel steering, tires, and brakes; member of the launch support team at Kennedy Space Center for Shuttle flights STS-61-A, STS-61-B, STS-61-C, and STS-51-L; in 1986 he worked at the NASA Headquarters Action Center in Washington, D.C., assisting with the "Challenger" accident investigations conducted by NASA, the Presidential Commission, and U.S. Congress.