Expedition 54 backup crew member Sergey Prokopev is seen in quarantine, behind glass, during a press conference, Saturday, Dec. 16, 2017 at the Cosmonaut Hotel in Baikonur, Kazakhstan. Expedition 54 prime crew members Soyuz Commander Anton Shkaplerov of Roscosmos, flight engineer Scott Tingle of NASA, and flight engineer Norishige Kanai of the Japan Aerospace Exploration Agency (JAXA) are scheduled to launch to the International Space Station aboard the Soyuz spacecraft from the Baikonur Cosmodrome on December 17. Photo Credit: (NASA/Joel Kowsky)

Expedition 54 backup crew members Jeanette Epps of NASA, left, Sergey Prokopev of Roscosmos, center, and Alex Gerst of ESA (European Space Agency), right, pose for a picture as the Soyuz rocket is rolled out to the pad, Friday, Dec. 15, 2017 at the Baikonur Cosmodrome in Kazakhstan. Expedition 54 Soyuz Commander Anton Shkaplerov of Roscosmos, flight engineer Scott Tingle of NASA, and flight engineer Norishige Kanai of the Japan Aerospace Exploration Agency (JAXA) are scheduled to launch at 2:21 a.m. Eastern Time (1:21 p.m. Baikonur time) on Dec. 17 and will spend the next five months living and working aboard the International Space Station. Photo Credit: (NASA/Joel Kowsky)

Expedition 54 prime crew members flight engineer Norishige Kanai of Japan Aerospace Exploration Agency (JAXA), left, Soyuz Commander Anton Shkaplerov of Roscosmos, center, and flight engineer Scott Tingle of NASA, right, pose for a picture with backup crew members of NASA, right, Sergey Prokopev of Roscosmos, center, and Alex Gerst of ESA (European Space Agency), right after donning their Russian Sokol suits in preparation for launch to the International Space Station Sunday, Dec. 17, 2017 in Baikonur, Kazakhstan. Launch of the Soyuz rocket will send Tingle, Kanai, and Shkaplerov on a five month mission aboard the International Space Station. Photo Credit: (NASA/GCTC/Andrey Shelepin)

iss056e098197 (7/23/2018) --- Russian Cosmonaut Sergei Prokopev, during Plasma Krystall-4 (PK-4) Experiment Interface Installation. PK-4 is a scientific collaboration between the European Space Agency (ESA) and the Russian Federal Space Agency (Roscosmos), performing research in the field of "Complex Plasmas".

iss056e078440 (July 5, 2018) --- Astronaut Alexander Gerst practices cardiopulmonary resuscitation (CPR) as cosmonaut Sergey Prokopev looks on during an emergency training session aboard the International Space Station. The onboard training provides crewmembers the opportunity to review safety procedures, communication methods and hardware necessary to manage a medical emergency.

Expedition 54 prime crew members flight engineer Norishige Kanai of the Japan Aerospace Exploration Agency (JAXA), left, Soyuz Commander Anton Shkaplerov of Roscosmos, second from left, flight engineer Scott Tingle of NASA, third from left, pose for a picture with backup crew members Jeanette Epps of NASA, third from right, Sergey Prokopev of Roscosmos, second from right, and Alex Gerst of ESA (European Space Agency), right, at the conclusion of a press conference, Saturday, Dec. 16, 2017 at the Cosmonaut Hotel in Baikonur, Kazakhstan. Expedition 54 Soyuz Commander Anton Shkaplerov of Roscosmos, flight engineer Scott Tingle of NASA, and flight engineer Norishige Kanai of Japan Aerospace Exploration Agency (JAXA) are scheduled to launch to the International Space Station aboard the Soyuz spacecraft from the Baikonur Cosmodrome on December 17. Photo Credit: (NASA/Joel Kowsky)

Expedition 54 prime crew members flight engineer Norishige Kanai of the Japan Aerospace Exploration Agency (JAXA), Soyuz Commander Anton Shkaplerov of Roscosmos, flight engineer Scott Tingle of NASA, along with backup crew members Jeanette Epps of NASA, Sergey Prokopev of Roscosmos, and Alex Gerst of ESA (European Space Agency), are seen as they enter a room for a press conference, Saturday, Dec. 16, 2017 at the Cosmonaut Hotel in Baikonur, Kazakhstan. Expedition 54 Soyuz Commander Anton Shkaplerov of Roscosmos, flight engineer Scott Tingle of NASA, and flight engineer Norishige Kanai of Japan Aerospace Exploration Agency (JAXA) are scheduled to launch to the International Space Station aboard the Soyuz spacecraft from the Baikonur Cosmodrome on December 17. Photo Credit: (NASA/Joel Kowsky)

iss056-s-002 (March 8, 2018) --- The official portrait of the Expedition 56 crew. In the front row from left are astronauts Drew Feustel of NASA and Alexander Gerst of the European Space Agency. In the rear from left are crew members Oleg Artemyev of Roscosmos, Ricky Arnold of NASA, Sergei Prokopev of Roscosmos and Serena Auñón-Chancellor of NASA.

iss057-s-002 (November 8, 2017) --- The official portrait of the five-member Expedition 57 crew. In the front row from left are Serena Auñón-Chancellor of NASA, Commander Alexander Gerst from the European Space Agency and Sergei Prokopev of Roscosmos. In the back row from left are Flight Engineers Aleksey Ovchinin of Roscosmos and Nick Hague from NASA.

iss057e074488 (11/7/2018) --- Russian Cosmonaut Sergei Prokopev, during the Plasma Krystall-4 (PK-4) Experiment. PK-4 is a scientific collaboration between the European Space Agency (ESA) and the Russian Federal Space Agency (Roscosmos), performing research in the field of "Complex Plasmas". Complex or dusty plasmas are plasmas which contain beside electrons, ions, and neutral gas in addition micro-particles, e.g., dust grains. Due to the strong influence of gravity on the micro-particles, most experiments on complex plasmas are strongly distorted or even impossible on earth, and therefore, require microgravity conditions.