Sergey Prokopyev

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. 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. 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.

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. 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.

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

He trained as backup flight engineer for Soyuz TMA-18M and ISS EP-18, training for a short-duration eight day stay on the ISS that was eventually flown by KazCosmos cosmonaut Aidyn Aimbetov. Unlike most backup assignments, his assignment to TMA-18M did not lead into a later prime crew assignment, therefore following the launch of TMA-18M 2 September 2016 Prokopyev did not rotated onto a prime crew immediately.

Following his graduation he was part of the specialization and improvement group for the ISS Russian Orbital Segment and Soyuz TMA-M spacecraft, he held this position until June 2015 when he was assigned to a backup crew.

In October 2010 Prokopyev was selected as a cosmonaut by Roscosmos, he began cosmonaut training February 2011, he graduated and gained the qualification of "test cosmonaut" in August 2012.

Prokopyev is married to Ekaterina Prokopyeva (née Negreyeva), who gave birth to their daughter, Anna, on 27 August 1997 and son, Timofei, on 23 February 2010.

Sergei Valeriyevich Prokopyev (Russian: Серге́й Вале́рьевич Проко́пьев , born 19 February 1975) is a Russian cosmonaut. On 6 June 2018 he launched on his first flight into space aboard Soyuz MS-09 and spent 196 days in space as a flight engineer on Expedition 56/57.