Expedition 52 flight engineers Sergey Ryazanskiy of Roscosmos, seated left, and Randy Bresnik of NASA are seen as they sign a guest book at the "Memorial working study of Yuri Gagarin" at the Gagarin Cosmonaut Training Center (GCTC), Monday, July 10, 2017 in Star City, Russia. The memorial study represents Gagarin's working study in the way it was abandoned by Gagarin on March 27, 1968 before leaving for the airfield for training flight that became his last.