of the
STS-127 mission Cassidy was selected as an astronaut candidate by
NASA in May 2004. In February 2006 he completed Astronaut Candidate Training, which included scientific and technical briefings, intensive instruction in
Space Shuttle and
International Space Station systems, physiological training,
T-38 Talon flight training, and water and wilderness survival training. Completion of this initial training qualified him for various technical assignments within the Astronaut Office and future flight assignment as a mission specialist. Cassidy and his six fellow crew members lifted off aboard
Endeavour from the
Kennedy Space Center on July 15, 2009. The seven astronauts docked with the ISS on July 17, joining the six-person
Expedition 20 crew commanded by Russian cosmonaut
Gennady Padalka. This marked the first time that 13 people had been in space together simultaneously. On July 22, 2009, Cassidy stepped outside the ISS with NASA astronaut
David Wolf for his first spacewalk. The two began work replacing batteries on the P6
Truss and continued work on installing the JEM-EF. The EVA was called off after 5 hours and 59 minutes for excess
carbon dioxide in Cassidy's suit. Over the course of STS-127, Cassidy participated in two more spacewalks with NASA astronaut
Thomas Marshburn. The two completed replacing the batteries on the P6 truss and completed the installation of the JEM-EF during two excursions lasting 7 hours and 12 minutes and 4 hours and 57 minutes, respectively. Cassidy's third spacewalk marked the completion of the Japanese Experiment Module, a feat that took three space shuttle missions starting with
STS-123. On July 31, 2009, Cassidy returned to the KSC
Shuttle Landing Facility, wrapping up his first spaceflight after 15 days in space.
Expedition 35/36 Cassidy was assigned to the
Expedition 35 crew as a flight engineer and flew to the ISS aboard
Soyuz TMA-08M (
US designation: 34S), which launched on March 28, 2013. On May 11, 2013, Cassidy and
Thomas Marshburn performed an unplanned spacewalk to replace a pump controller box suspected to be the source of an ammonia coolant leak. Cassidy participated in two US spacewalks from the ISS in June/July 2013. During the EVA, Cassidy took his
space selfie. That photo became one of the best selfies of 2013 listed by many news sites.
Chief of the Astronaut Office Cassidy was named the 15th
Chief of the Astronaut Office at NASA in July 2015, succeeding
Bob Behnken. On June 2, 2017, Cassidy was replaced by
Patrick G. Forrester as Chief of the Astronaut Office and was returned to normal flight status.
Expedition 62/63 in
Kazakhstan, April 9, 2020 Cassidy launched onboard
Soyuz MS-16 on April 9, 2020, as part of Expedition 62. He was the ISS commander for
Expedition 63, which consisted of Cassidy and Russian cosmonauts
Ivan Vagner and
Anatoli Ivanishin. Cassidy was joined by fellow NASA astronauts
Doug Hurley and
Bob Behnken on May 31, 2020, with the docking of
Crew Dragon Demo-2. Cassidy and his crew returned to Earth on October 21, 2020. They landed in Dzhezkazgan, Kazakhstan at 10:54 pm. Cassidy's last two years as an astronaut were the central feature of the
Disney+ docuseries Among the Stars. The series was removed from Disney+ on May 26, 2023, amidst the Disney+ and
Hulu purge. == Post-NASA career ==