Sergey Ryazanskiy waits to board a Soyuz training mockup works inside as part of final crew qualification exams.

At the Gagarin Cosmonaut Training Center in Star City, Russia, Expedition 51 backup crewmember Sergey Ryazanskiy of the Russian Federal Space Agency (Roscosmos) waits to board a Soyuz training mockup March 30 as his crewmate, Randy Bresnik of NASA, works inside as part of final crew qualification exams. They are backups to Fyodor Yurchikhin of Roscosmos and Jack Fischer of NASA, who will launch April 20 on the Soyuz MS-04 spacecraft from the Baikonur Cosmodrome in Kazakhstan for a four and a half month mission on the International Space Station. Credit: NASA/Rob Navias