Sergey Prokopyev (cosmonaut)

Prokopyev was originally meant to be Soyuz commander on Soyuz MS-08 and flight engineer on ISS Expedition 55/56 although due to Russian budget cutbacks reducing the number of crew members on the ISS Russian segment he was removed from the flight and instead was assigned as backup Soyuz commander Soyuz MS-07 and flight engineer/ISS commander for Expedition 54/55.[3] Following the launch of Expedition 54/55 he was assigned as prime crew flight engineer for Expedition 56/57 alongside German Alexander Gerst, who would serve as ISS commander for Expedition 57, and NASA astronaut Jeanette Epps, who would later be replaced by astronaut Serena Aunon-Chancellor.

The trio launched on Soyuz MS-09 from the Baikonur Cosmodrome on 6 June 2018 and spent approximately two days free flying in Low Earth orbit before the rendezvoused and docked to the ISS on 8 June, officially joined the Expedition 56 alongside American astronauts Andrew Feustel and Richard Arnold as well as Russian cosmonaut Oleg Artemyev.[4] He performed his first Spacewalk alongside Artemyev on 15 August, the two spent 7 hours and 46 minutes working outside the station where they installed a Roscosmos-DLR experiment for observing animal migration, called ICARUS onto the outside of the station and manually deployed four CubeSat into orbit.[5] On 29 August an air leak was observed inside the station, this was later discovered to be caused by a hole aboard Soyuz MS-09, Prokopyev's spacecraft.[6]

Following the departure of Soyuz MS-08 on 4 October 2018, Prokopyev, Gerst and Aunon-Chancellor transferred over to Expedition 57, they were scheduled to be joined by Russian cosmonaut Aleksey Ovchinin and American astronaut Nick Hague on 11 October, although the flight was aborted during launch cancelling their arrival. In order to avoid de-crewing the space station, the landing of MS-09 was delayed from 11 December to 20 December, while the launch of Soyuz MS-11 was advanced from 20 December to 3 December, giving the two spacecraft and their six crew members a 17 day hand-over period. Prokopyev and his two crew mates worked together as a crew of three until 3 December 2018, when Soyuz MS-11 carrying Russian cosmonaut Oleg Kononenko, CSA astronaut David Saint-Jacques and NASA astronaut Anne McClain.[7] During his final days on the ISS on 11 December 2018, he and Kononenko preformed a spacewalk to inspect the hole on Soyuz MS-09, they took imagines and applied a thermal blanket to the damaged area on the Soyuz's "orbital module", towards the end of the excision the two also retrieved some science experiments from the outside of the station.[8]

He, Gerst and Aunon-Chancellor returned to Earth on 20 December 2018, ending Prokopyev's first spaceflight after 196 days in space.[9]