In 1962, space travel wasn't what you'd call an "exact" science. NASA was only a few years old and nobody really knew how humans would cope outside the atmosphere. Now, 50 years after his historic orbit, John Glenn recalls what his doctors thought would happen in zero gravity.

Physicians worried that, among other maladies, Glenn's eyeballs would deform from the lack of gravity and prevent him from piloting the escape vehicle if he needed to make an emergency reentry. They also believed that his inner ears would cease to function, resulting in paralyzing vertigo, and that he'd be unable to swallow without the aid of the Earth's pull.

If Glenn was worried, he didn't let on. Thankfully, his flight aboard Friendship 7 on February 20th, 1962 was a complete success. He categorized the concerns as "so primitive now, they're almost laughable " during an address to NASA staff at the Kennedy Space Center on Friday. [Business Insider]