On the 50th anniversary of the Project Mercury launch that sent Alan Shepard hurtling into the sky at more than 100 mph to make him the second person -- and first American -- to achieve spaceflight, LIFE.com has pulled together a collection of never-before-seen photographs of Shepard and his fellow astronauts preparing for the mission that would put them in the history books. Most of the photos that LIFE was able to unearth were taken by Ralph Morse, a man known as "the 8th Mercury astronaut," a name given to him by the legendary John Glenn because of his presence throughout the entire project.

View more photos at LIFE.com.

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