Anniversary of 50 Years of Man in Space [VIDEO]

When John Glenn took off on 'Friendship 7', the United States' first orbital spaceflight 50 years ago today (Feb. 20), NASA scientists weren't sure he would even survive the trip.

Before John Glenn completed his three Earth orbits, no American had spent more than 15 minutes in space. NASA medical personnel had a long list of worries, not the least of which were whether or not his eyes would function properly in microgravity. "They were enough concerned about it, we actually put a little miniaturized eye chart at the top of the instrument panel," Glenn commented. "And that's still in Friendship 7, up in the Smithsonian [National Air and Space Museum]."

"There were a lot of unknowns in the early days of spaceflight," former astronaut Scott Carpenter, who completed an orbital mission of his own in May 1962, said Friday (Feb. 17) at a NASA event commemorating Glenn's flight. "We were considered guilty of being unable to fly in space and required to prove our innocence, counter to the American custom."

Though in the end everything worked, Glenn's success was far from assured.

"His odds of not surviving this was about one in six," former astronaut Steve Lindsey, who flew with Glenn on the space shuttle Discovery's STS-95 mission in 1998, said in a recent NASA video. "So it was an extremely high-risk, unknown effort that they were going into, having never done it before."

Source: SPACE.com: All about our solar system, outer space and exploration