Sept. 17, 1959, The first powered X-15 flight was made on , and 199 flights were made between 1959 and 1968 by the three X-15s which were built. The X-15, designed to provide data on material and human factors of high-speed, high-altitude flight, madethe first manned probes into the lower edges of space. It was built for speeds of up to 4,000 mph and altitudes of 50 miles, but these goals were exceeded on numerous occasions.

Several X-15 pilots earned "astronaut" rating by attaining altitudes above 50 miles. The X-15 flight program contributed significantly to the Mercury, Gemini, and Apollo projects. The X-15 was carried aloft by a B-52 and was released at about 45,000 feet and 500 mph. Its rocket engine then fired for the first 80 to 120 seconds of flight. The remainder of the 10 to 11 minute flight was powerless and ended with a 200 mph glide landing on a dry lake bed.