On a perfectly still August morning in 1960, Air Force Captain Joseph Kittinger lifted off in a helium balloon from an abandoned airstrip in New Mexico, floating upwards into the clouds. When his open gondola reached 100,000 feet, nearly 20 miles above the earth, Kittinger disconnected his onboard oxygen supply, said a prayer, and stepped off into the unknown. Within seconds, he was hurtling at over four hundred miles per hour through temperatures nearing one hundred degrees below zero.

Kittinger’s daring feat was part of a Cold War research program called Project Manhigh that began testing the limits of human endurance at the very edge of space nearly a decade before President John F. Kennedy committed the nation to sending a man to the moon. The pioneering group of Air Force scientists and pilots collected data about the biological and technical factors required to support human activity in space. Space Men tells the little-known story of the men whose scientific experiments in the stratosphere laid critical groundwork for NASA’s manned space program, helping to make the very idea of space trips a reality.