Tracy C. Dyson

Tracy Caldwell Dyson, born in 1969 in Arcadia, California, is a scientist by training who reached the astronaut corps through the laboratory bench. She earned a bachelor's degree in chemistry from California State University, Fullerton, and a Ph.D. in chemistry from the University of California, Davis, conducting surface chemistry research before NASA selected her in 1998. A private pilot conversational in both Russian and American Sign Language, she is also an accomplished vocalist who fronts the astronaut band Max-Q, a talent that later produced a memorable moment when she sang from orbit. Her mix of hard science and public artistry has made her one of NASA's most recognizable veteran fliers.

Dyson has flown three times over nearly two decades. Her first flight was as a mission specialist aboard Space Shuttle Endeavour on STS-118 in August 2007, a station assembly mission. She returned for her first long-duration stay on Expeditions 23 and 24, launching aboard Soyuz TMA-18 in April 2010 and living aboard the International Space Station until September 2010. That increment tested her under pressure: when a critical ammonia coolant pump failed, she carried out a demanding series of three contingency spacewalks in August 2010 alongside Douglas Wheelock to remove and replace the failed unit, a repair that ran across multiple excursions and nearly twenty-three hours outside. Her third flight came in 2024, when she launched aboard Soyuz MS-25 on March 23 with cosmonaut Oleg Novitsky and Belarusian spaceflight participant Marina Vasilevskaya for Expeditions 70 and 71, returning to Earth on September 23, 2024. During that stay she began a spacewalk with Michael Barratt on June 24, 2024 that was called off almost immediately when her suit's cooling system leaked water into the airlock, ending the excursion after only about half an hour. In all she has completed four spacewalks totaling roughly twenty-three and a half hours of extravehicular time.

Dyson's legacy rests on her versatility and her endurance across three missions separated by many years. Recognized with the NASA Spaceflight Medal, the NASA Exceptional Service Medal, and Russia's Medal for Merit in Space Exploration for her work aboard the joint station, she has been both a capable spacewalker in emergencies and a bridge to the public through music, having sung the U.S. national anthem live from the station. An active NASA astronaut and mentor to newer crew members, she remains focused on advancing the station science that will enable exploration beyond low Earth orbit, carrying the credibility of a chemist who has also done the hardest physical work the job demands.