In the late 1940s, the notion of space travel lived squarely in the realm of science fiction. But a young Army doctor named John Paul Stapp saw no limit to how far mankind could go—he had his eyes set on the heavens. By the 1950s and early '60s, a small band of high-altitude pioneers exposed themselves to the extreme forces of space, long before NASA's acclaimed Mercury 7 would make headlines. U.S. Air Force pilots and scientists lay the groundwork for the U.S. space program through Project Manhigh between 1955 and 1958. With a fraction of NASA's budget and none of its renown, Stapp's Project Excelsior would send Captain Joseph Kittinger to a record-breaking 102,800 feet above Earth on August 16, 1960, lifted not by rocket, but by balloon. Though largely forgotten, this group of daring explorers would be the first to venture into the frozen vacuum on the edge of our world, testing the very limits of human physiology and ingenuity in this deadly realm.

Meet Nikola Tesla, the genius engineer and tireless inventor whose technology revolutionized the electrical age of the 20th century. Regarded by many historians as an eccentric genius, Tesla gained international fame for his invention of a system of alternating current that made possible the distribution of electricity over vast distances and is the basis for the electrical grid that powers 21st-century life. But the visionary Tesla imagined much more — robots, radio, radar, remote control, the wireless transmission of messages and pictures, and harnessing the wind and sun to provide free energy to all. A showman, he dazzled his scientific peers who flocked to see him demonstrate his inventions and send thousands of volts of electricity pulsing through his body. His fertile but undisciplined imagination was the source of his genius but also his downfall, as the image of Tesla as a "mad scientist" came to overshadow his reputation as a brilliant innovator. Even before his death in 1943, he was largely forgotten, his name obscured by Thomas Edison — his hero, one-time employer, and rival. But it is his exhilarating sense of the future that has inspired renewed interest in the man, as his once scoffed-at vision of a world connected by wireless technology has become a reality.