Tracy Caldwell Dyson is an American chemist and NASA astronaut. Caldwell Dyson 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 hrs of EVA.