Tracy C. Dyson was selected as an astronaut by NASA in 1998. The California native has a Ph.D. in Chemistry, and is a veteran of three space flights. Dr. Dyson has designed, constructed and implemented electronics and hardware for the study of atmospheric gas phase chemistry, and has developed and presented numerous papers on methods of chemical ionization for the spectral interpretation of trace compounds. In 2007, Dyson flew aboard the space shuttle Endeavor on STS-118, where she served as a mission specialist. In 2010, she served as flight engineer for Expedition 23/24. She has logged a total of 373 days in space, including over 23 hours in four spacewalks. Most recently, Dyson launched to the International Space Station on March 23, 2024, as a flight engineer on the Soyuz MS-25 spacecraft. Dyson spent six months aboard the station as an Expedition 71 flight engineer, conducting science experiments and maintaining the space station. It was her second long-duration spaceflight and third mission overall.