Summary and Key Points: The X-15 program, spanning 199 flights between 1959 and 1968, pushed the boundaries of aeronautics into the hypersonic realm. -Capable of reaching altitudes of 102,000 feet, ...

Dropped in mid-air from beneath the wings of a B-52 mothership, the X-15 A-2 ignited its powerful rocket engine and streaked into the upper-atmosphere. Previous burns only lasted 90-seconds, but on ...