Peggy Annette Whitson (born February 9, 1960) is an American biochemistry researcher, and astronaut working for Axiom Space. She retired from NASA in 2018, after serving as the 13th chief of the Astronaut Office. Over all her missions, Whitson has accumulated a total of 695 days in space, more than any other American or woman.
Her first NASA space mission was in 2002: an extended stay aboard the International Space Station (ISS) as a crew member of Expedition 5. On her second mission, Expedition 16 in 2007-2008, she became the first woman to command the ISS. In 2009, she became the first woman to serve as NASA's Chief Astronaut, the most senior position in the NASA Astronaut Corps. In 2017, Whitson became the first woman to command the International Space Station twice. Her 289-day flight was the longest single space flight by a woman until Christina Koch's 328-day flight.
Whitson holds the records for the oldest woman spacewalker and the most spacewalks by a woman (10). Whitson's cumulative EVA time is 60 hours, 21 minutes, which places her in seventh place for total EVA time. At age 57 on her final NASA flight, she was the oldest woman ever in space at that time - a record broken in a 2021 sub-orbital flight by Wally Funk. She is still the oldest woman to orbit the Earth, a record she set in 2025, at 65.
On June 15, 2018, Whitson retired from NASA. She later became a consultant for Axiom Space. She served as the commander of Axiom Mission 2 in 2023 and Axiom Mission 4 in 2025.
Whitson was included in Time magazine's 100 Most Influential People of 2018.
Whitson grew up on a farm outside the town of Beaconsfield, Iowa, with her sister, Kathy, her brothers, Brian and Hugh, and her parents, Keith and Beth. Her parents were farmers. She decided to become an astronaut after she watched the first Moon landing on television as a child in 1969. Whitson graduated from Mount Ayr Community High School in 1978 and received a Bachelor of Science degree in biology and chemistry from Iowa Wesleyan College in 1981. She then went on to earn her doctorate degree in biochemistry from Rice University in 1986 under the direction of Kathleen Matthews, then continued at Rice as a Robert A Welch Post-doctoral Fellow until October 1986. She is married to Clarence F. Sams.
After her fellowship at Rice, she began working at Johnson Space Center in Houston, Texas, as a National Research Council Resident Research Associate. From April 1988 until September 1989, Whitson served as the Supervisor for the Biochemistry Research Group at KRUG International, a medical sciences contractor at NASA-JSC.
From 1991 through 1997, Whitson became an adjunct assistant professor in the Department of Internal Medicine and the Department of Human Biological Chemistry and Genetics at the University of Texas Medical Branch in Galveston, Texas. In 1997, Whitson began teaching as adjunct assistant professor at Rice University in the Maybee Laboratory for Biochemical and Genetic Engineering.
From 1992 to 1995, she served as project scientist for the Shuttle-Mir Program, then until 1996, as deputy division chief for the Medical Sciences division at the Johnson Space Center.
From 1989 to 1993, Whitson worked as a research biochemist in the Biomedical Operations and Research Branch at NASA-JSC. From 1991 to 1993, she served as technical monitor of the Biochemistry Research Laboratories in the Biomedical Operations and Research Branch. From 1991 through 1992, she was the payload element developer for Bone Cell Research Experiment (E10) aboard SL-J (STS-47), and was a member of the US-USSR Joint Working Group in Space Medicine and Biology. In 1992, she was named the project scientist of the Shuttle-Mir Program (STS-60, STS-63, STS-71, Mir 18, Mir 19), and served in this capacity until the conclusion of the Phase 1A Program in 1995. From 1993 through 1996, Whitson held the additional responsibilities of the deputy division chief of the Medical Sciences Division at NASA-JSC. From 1995 to 1996, she served as co-chair of the U.S.-Russian Mission Science Working Group.
In April 1996, Whitson was selected as an astronaut candidate; she started training in August 1996. Upon completing the two years of training and evaluation, she was assigned technical duties in the Astronaut Office Operations Planning Branch, and served as the lead for the Crew Test Support Team in Russia from 1998 to 1999. In June 2003, Whitson commanded the NEEMO 5 mission aboard the Aquarius underwater laboratory, living and working underwater for 14 days. From November 2003 to March 2005, she served as deputy chief of the Astronaut Office. From March 2005 to November 2005, she served as chief of the Station Operations Branch, Astronaut Office.
Whitson was appointed NASA Chief of the Astronaut Office in October 2009, replacing Steven W. Lindsey. Whitson was the first female, and first non-pilot to serve as Chief Astronaut. She resigned when she went back on active flight status in July 2012, replaced by Robert Behnken. Whitson has also served twice as the commander of the International Space Station.
She became the Director of Human Space Flight for Axiom Space in 2021.
In January 2021, Axiom announced she would be back-up commander of Axiom Mission 1, raising the possibility that she could fly a later Axiom Space mission.
On 21 May 2023, Whitson returned to space as the commander of the second Axiom mission Axiom Mission 2, docking with the ISS and spending 8 days in space. She was again back-up commander of Axiom Mission 3.
On 26 June 2025, Whitson served as the commander of the fourth Axiom mission Axiom Mission 4.
She is currently the Senior Vice President of Human Space Flight Training for Axiom Space.
The Expedition 5 crew launched on June 5, 2002, aboard STS-111 and docked with the International Space Station on June 7, 2002. During her six-month stay aboard the Space Station, Whitson installed the Mobile Base System, the S1 truss segment, and the P1 truss segment using the space station remote manipulator system; performed a 4-hour and 25 minute spacewalk in a Russian Orlan space suit to install micrometeoroid shielding on the Zvezda Service Module; and activated and checked out the Microgravity Sciences Glovebox, a facility class payload rack.