Robert Heinlein may have written about it in his article Pravda means 'Truth', that while traveling in Vilnius, in the USSR, he was told by Red Army cadets that the Soviet Union had launched a man into orbit that day, but that later the same day their claim was denied.

I suspect that the facts would have been uncovered and published sometime during or following the downfall of the Soviet Union, as has the Katyn Massacre.

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Eudaimonia