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 fourth to Gennady Padalka, Oleg Kononenko 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.

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