10. The X-15 program was not entirely problem-free
The X-15 program included 199 flights of hypersonic aircraft, which were carried into the air by B-52s. After reaching the predetermined launch altitude the X-15 was released. The rocket plane dropped from the bomber’s wing, and its pilot fired the rocket motors. The X-15 carried several different pilots to altitudes that exceeded fifty miles, entering what is officially considered space. Until the release of the X-15, a chase plane flew with the mothercraft as an observer. After the X-15 launched the modified B-52 circled, eventually returning to base. The majority of the B-52 launch flights were piloted by Fitz Fulton, who years later flew the modified Boeing 747 used to launch the early evaluation and test version of the Space Shuttle. Among the X-15 pilots were Joe Engle, who later flew in the Shuttle, and Neil Armstrong, the first man to walk on the moon.
Though the NASA B-52s performed their missions well, not all of the X-15 flights were successful. On November 15, 1967, USAF Major Michael Adams piloted the rocket plane to an altitude of 266,000 feet, qualifying him as an astronaut. During descent, the aircraft encountered problems which threw it into a violent spin while traveling five miles over the speed of sound (Mach 5). As the descent continued the aircraft suffered forces which exceeded its design limits and broke apart, killing Major Adams. The exact cause of the crash was never fully determined, though the investigative board speculated the pilot deviated from his flight path through distraction and possibly vertigo. Major Adams was the only pilot to lose his life as a result of an accident involving the X-15.