February 24, 2016 11:50 AM EST

Think of early American astronauts, and a few names probably come to mind: Ed White, Neil Armstrong, John Glenn. But, as made clear by the new American Experience documentary Space Men—premiering on PBS on Mar. 1—those famous men stood on the metaphorical shoulders of the “pre-astronauts” who tested the skies first. Under the aegis of the Air Force, not NASA, they had risked their lives to see how high, how fast and how far the human body could go before collapsing.

This exclusive clip features one of those men, Lt. Col. John Paul Stapp, an Air Force surgeon who had earned the nickname of “the fastest man on Earth.” Though many of his experiments were conducted on other men, his most risky tests were suited for only one subject: himself.

Stapp attempted to replicate on Earth the force that would be felt by space pilot ejecting from his craft thousands of feet above the ground. To do so, he rode in a specially designed sled capable of going hundreds of miles per hour, slamming to a stop to see how his body reacted to the impact. As TIME wrote in its 1955 coverage of the mission, “the data [such missions] produce are urgently needed in an age when man is opening up dreamlike new frontiers of space and speed.”

But how would his body react? Watch to find out.

Read the issue featured in the clip above, here in the TIME Vault: The Fastest Man on Earth

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Write to Lily Rothman at lily.rothman@time.com.

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