it was happy birthday to you
"On 12 April 1961, Yuri Gagarin became the first man to travel into space, launching to orbit aboard the Vostok 3KA-3 (Vostok 1). His call sign in this flight was Kedr (Cedar; Russian: Кедр). During his flight, Gagarin famously whistled the tune "The Motherland Hears, The Motherland Knows" (Russian: "Родина слышит, Родина знает"). The first two lines of the song are: "The Motherland hears, the Motherland knows/Where her son flies in the sky". This patriotic song was written by Dmitri Shostakovich in 1951 (opus 86), with words by Yevgeniy Dolmatovsky."<br />
Admittedly whistling isn't singing, but as he was the first, by several years, and did it all alone, he gets my vote ?<br />
"99 million bottles of beer on the wall, 99 million bottles of beer, if one of those bottles should happen to fall..."<br />
Hey, it was a long trip and they had to do something to pass the time.
This is a guess - It’s a wonderful World by Louie Armstrong! Cheers!