Donald Alan Thomas, Ph.D. (born May 6, 1955) is an American engineer and a former NASA astronaut. Selected by NASA in January 1990, Dr. Thomas became an astronaut in July 1991. Thomas has served in the Safety, Operations Development, and Payloads Branches of the Astronaut Office. He was CAPCOM (spacecraft communicator) for Shuttle missions STS-47, 52 and 53. From July 1999 to June 2000 he was Director of Operations for NASA at the Gagarin Cosmonaut Training Center in Star City, Moscow, Russia. A veteran of four space flights, he logged over 1,040 hours in space. He was a mission specialist on STS-65 (July 8, 1994 – July 23, 1994), STS-70 (July 13, 1995 – July 22, 1995), STS-83 (April 4, 1997 – April 8, 1997) and STS-94 (July 1, 1997 – July 17, 1997). Initially assigned to the ISS Expedition 6 crew, his flight assignment withdrawal resulted from a medical issue affecting long duration space flight qualifications. In his last assignment he served as the International Space Station Program Scientist overseeing NASA experiments performed on the ISS. Thomas retired from NASA in July 2007.