Tracy Caldwell Dyson is an American chemist and NASA astronaut. She was a mission specialist on Space Shuttle Endeavour flight STS-118 in August 2007 and part of the Expedition 23 and Expedition 24 crew on the International Space Station from April 2010 to September 2010. She has completed three spacewalks, logging more than 22 hours of extravehicular activity. She is scheduled to return to space on March 21, 2024 for a third time aboard Soyuz MS-25 for a six-month mission onboard the ISS.