The first American astronaut to orbit the Earth was named Alan Shepard, and he left Earth on May 5, 1961. He wasn't the first human in space -- a Soviet astronaut named Yuri Gagarin has that distinction. But Shepard was NASA's entry into the annals of human space flight.
It was a nervous day for NASA. The countdown, divided for the first time into two parts so Shepard didn't have to spend an entire day on the launch pad, took more than 24 hours. NASA halted it several times for minor equipment checks, and finally it was T-15 minutes to liftoff. Shepard was onboard, the pilots of the launch vehicle were ready, and all systems were go. Then the clouds moved in.
The weather wasn't a problem for the launch. But it was a problem for the photographer covering the biggest NASA event to date. So NASA postponed the launch until the clouds cleared. During that hold, one of the orbiter's power inverters showed signs of trouble, and engineers fixed the problem in 86 minutes. At T-15, NASA decided to double-check a piece of navigation equipment.
The rest of the countdown went uninterrupted, and the launch, at 9:34 AM, about 25 hours after the start of the countdown, went off without a hitch. Shepard reached Earth orbit at an altitude of 116.5 miles (187.5 km). He spent 15 minutes and 28 seconds up there, travelling 303 miles around the Earth at 5,134 miles per hour (8,262 kph) [source: NASA]. When he splashed down in the Atlantic Ocean, he had completed a perfect mission and led the way for every NASA manned mission to come.
The manned mission that put NASA in the record books came eight years later. It was so monumental that conspiracy theorists question its validity to this day.