Fincke comes with plenty of spaceflight experience, as this will be his fourth trip to space.
Boeing plans to launch its first Starliner capsule and not using a crew this spring, adopted by launch with astronauts this summer season to the International Space Station. During this flight, Fincke and his three ISS crewmembers welcomed STS-126/Endeavour and Eric Boe to the Station and also oversaw delivery of the final set of Solar Arrays for the Station on STS-119/Discovery.
Boeing and SpaceX are both designing commercial crew capsules to ferry astronauts to and from the International Space Station in a bid to end NASA's sole reliance on Russian Soyuz spacecraft for transportation to low-Earth orbit.
Boe was appointed to this flight in August of 2018, alongside eight different astronauts partaking in the inaugural missions for NASA's Commercial Crew Program. NASA doesn't offer much in the way of details surrounding the decision to shuffle the astronauts other than to say that Boe 'is unable to fly due to medical reasons.' Boe was originally announced as a member of the crew in August 2018.
That crew change prompted questions of exactly why she was removed from the mission; as a rule, NASA does not discuss crew assignments - or reassignments as the case may be - and never divulges exactly why certain astronauts are chosen and others are not.
Fincke launched on the two-person Expedition 9 mission on 18 April 2004 - when Station operations were restricted to just two crewmembers in the wake of the Space Shuttle Columbia accident. Fincke spent 381 days in space on those three missions, including more than 48 hours of EVA time on nine spacewalks. During that mission, Fincke broke the previous USA record for longest time in space.
Fincke was then assigned to his first and only Space Shuttle mission, STS-134.
Astronauts Robert Behnken, a two-flight shuttle veteran and former chief of NASA's astronaut office, and Doug Hurley, Ferguson's co-pilot for the final shuttle mission, were assigned to the first piloted flight of SpaceX's Crew Dragon capsule. However, NASA's contract with Roscosmos is expected to expire in November 2019.