"There were all kinds of wild fears that a man could lose his mind in zero gravity, lose his ability to make rational decisions," Oleg Ivanovsky, who oversaw the construction and launch of Gagarin's spacecraft, told The Associated Press. Even though Vostok's operation was automatic, controllers wondered if weightlessness could cause Gagarin to go crazy and try to take over command of the capsule. As added protection, the engineers added a three-digit security code that Gagarin would have to enter to command the spacecraft.
Ultimately, the point was moot. Gagarin's spacecraft launched -- and landed -- safely.
4. Gagarin Really Was Crazy
Well, no, he wasn't crazy, but he was preternaturally calm about risking his life. Russian accounts show that Korolyev, the chief designer, was so anxious about Gagarin's flight that he had chest pains, and didn't sleep the night before.
Gagarin, on the other hand, declined a sleeping pill and is reported to have slept well. Shortly before launch, his pulse was measured at 64 beats per minute. Not a sign of a worried man.
3. First Atheist in Space?
After the flight, Gagarin was widely quoted in the West as having said from space, "I don't see any God up here."
Not quite. Soviet leader Nikita Khrushchev said something similar after he welcomed the returning hero to Moscow. Gagarin, for his part, said he hummed a patriotic song in orbit:
"The Motherland hears, the Motherland knows/Where her son flies in the sky."
2. All the Soviets Really Wanted Was to Beat the U.S.
Partly true. Siddiqi writes that the Soviet target date for launching Vostok was determined by publicity about NASA's Project Mercury, which planned to launch its first man early in 1961. Gagarin beat Alan Shepard into space by all of 23 days.
But Vostok had been in the planning since at least 1959. And by sheer luck for the Soviets, the Americans had a rocket failure in 1960 that caused them to order one extra test flight -- in March 1961 -- before launching Shepard in May. If not for that, the Americans would have been first.
There is some irony here. True, Apollo 11 ultimately beat the Soviets to the moon in 1969. But the U.S. astronaut program has searched for direction since then, and the Obama administration has ordered a pause after the space shuttles finish assembly of the International Space Station this year. For several years after, the only way for Americans to launch into space may be on board Russian Soyuz spacecraft.
1. Yuri Gagarin, National Icon
By the mid-1960s, two space heroes stood above all others in the world's imagination: the American John Glenn and the Soviet Gagarin. Both were so popular that their governments worried about losing them by letting them fly again.
Glenn got the message. He left NASA after his Friendship 7 flight in 1962, running for the Senate and, later, the presidency. Only when his political career was winding down did he persuade NASA to let him ride the space shuttle Discovery in 1998. By then he was 77.
Gagarin was different, and he let his bosses know it.
"They basically thought he was too politically valuable to risk on a second flight," said Robert Pearlman, editor of the website CollectSpace.com. "He kept pushing it back into their faces that he wanted to fly."
Gagarin was killed in a jet accident in 1968, reportedly while training for a space mission. He was only 34 years old.
ABC News' Ki Mae Heussner contributed reporting for this story.