Sergei Konstantinovich Krikalev (Russian: Сергей Константинович Крикалёв, also transliterated as Sergei Krikalyov; born 27 August 1958) is a Russian mechanical engineer, former cosmonaut and former head of the Yuri Gagarin Cosmonaut Training Center. As a prominent rocket scientist, he is a veteran of six space flights and ranks third to Gennady Padalka and Yuri Malenchenko for the most time spent in space: a total of 803 days, 9 hours, and 39 minutes.Krikalev was stranded on board the Mir during the dissolution of the Soviet Union. As the country that had sent him into space no longer existed, his return was delayed and he stayed in space for 311 consecutive days, twice as long as the mission had originally called for.He retired as a cosmonaut in 2007 and was working as vice president of Space Corporation Energia. From 2009 to 2014, he headed the Yuri Gagarin Cosmonaut Training Center.