The North American X-15 was a rocket-powered aircraft developed in the 1950s to explore the boundaries of flight. It was part of a joint program by NASA and the United States Air Force and aimed to gather data on hypersonic flight and the effects of high-altitude conditions. The X-15 could reach speeds of over 4,500 miles per hour and altitudes exceeding 350,000 feet. The aircraft made a total of 199 flights between 1959 and 1968, providing valuable information that contributed to the development of future spacecraft, including the Space Shuttle. Pilots of the X-15 included notable figures like Neil Armstrong and Chuck Yeager, who pushed the limits of aviation technology.