Andrew Sydney Withiel "Andy" Thomas, AO is an Australian and American aerospace engineer and a former NASA astronaut. He has dual nationality; he became a U.S. citizen in December 1986, hoping to gain entry to NASA's astronaut program. He is married to fellow NASA astronaut Shannon Walker.

Shannon Walker is an American physicist and a NASA astronaut selected in 2004. She launched on her first mission into space on June 25, 2010, onboard Soyuz TMA-19 and spent over 163 days in space.