The X-15 program bridged the chasm between atmospheric flight and spaceflight. Twelve pilots, including a young Neil Armstrong, flew 199 missions between 1959 and 1968, gathering data that shaped Mercury, Gemini, Apollo, and the Space Shuttle[^7]. The ship’s Inconel-X skin glowed cherry-red on reentry; its reaction controls steered by nitrogen jets where rudders no longer bit. Walker’s flight remains a monument to the brief, brilliant age of the rocket plane — the moment when an aircraft became a spacecraft, and a pilot became an astronaut while still wearing wings.