On the morning of May 5, 1961, 45 million Americans held their breath as Alan Shepard sat atop a Redstone rocket at Cape Canaveral’s Launch Complex 5. The 37-year-old Navy test pilot had been waiting over four hours through a series of maddening delays — so long, in fact, that he famously had to urinate in his spacesuit when no bathroom break was possible. But when the countdown reached zero at 9:34 AM EDT, Freedom 7 roared to life and carried Shepard on a 15-minute ride that changed the course of American history.

Mercury-Redstone 3 was a suborbital flight — a ballistic arc that reached an apogee of 116.5 miles before arcing back down to splashdown 302 miles downrange in the Atlantic Ocean. The flight lasted just 15 minutes and 28 seconds, but it packed an extraordinary amount of activity. Shepard experienced 5 minutes of weightlessness, manually controlled the spacecraft’s attitude using the hand controller — proving that a human pilot could function effectively in space — and observed the Earth through the periscope. He endured a punishing 11.6 G during reentry, the highest G-force any Mercury astronaut would experience.

The mission was a triumph. Shepard splashed down safely and was hoisted aboard a helicopter, then delivered to the recovery carrier USS Lake Champlain. He became an instant national hero. President Kennedy called to congratulate him, and three weeks later, on May 25, JFK stood before Congress and declared America’s goal of landing a man on the Moon before the decade was out. Shepard’s 15-minute flight had given the nation the confidence it needed to aim for the impossible.

Shepard would go on to command Apollo 14 in 1971, walking on the Moon and famously hitting two golf balls on the lunar surface. But it all started here — squeezed into a tiny capsule on a converted ballistic missile, proving that America could put a man in space and bring him home safely.