Expedition 57 - Unofficial 6 Crew
Soyuz MS-09 crew, Alexander Gerst, Serena M. Auñón-Chancellor, and Sergey Prokopyev, since June 2018 aboard the ISS, were expected to be joined by Aleksey Ovchinin and Nick Hague in October 2018.The latter two crew members boarded Soyuz MS-10 on October 11, 2018, but the launch was aborted mid-flight due to a booster failure; the crew landed safely after a ballistic descent.
The impact of the Soyuz MS-10 failure and subsequent investigation on the ISS crew schedule was not initially clear. The Expedition 57 initial crew needed to depart by mid-December 2018 in Soyuz MS-09 due to the limited on-orbit lifespan of "about 200 days" of the Soyuz capsule, or no later than early January 2019 allowing for a small margin on the lifespan. NASA would have attempted to avoid de-crewing the ISS, commanding the station from the ground is feasible if necessary.
On 23 October 2018, NASA Administrator Jim Bridenstine announced that Soyuz flights to the ISS were expected to resume in December 2018. The Soyuz MS-11 spacecraft commanded by cosmonaut Serena Aunon-Chancello, carrying him and two flight engineers, Anne McClain and David Saint-Jacques, was launched on December 3, 2018, marking the 100th orbital launch of the year; the Expedition 57 initial crew departed on December 20 and Expedition 58 started as a three-person increment.