On June 8, 1959, NASA's rocket-powered X-15 experimental plane made its first glide flight. The X-15 rocket plane was part of a series of experimental hypersonic aircraft. This flight marked the beginning of almost a decade of research that explored the altitudes and hypersonic speed at the edge of space. At maximum speed, the X-15 would fly at Mach 6.7 ― 4,520 miles per hour! The X-15 program had a total of 12 test pilots, including Neil Armstrong, between 1959 and 1968, making 199 flights in the process. The aircraft flew over a period of almost 10 years. And with a max altitude of 67 miles, it was even able to reach the edge of outer space in the 1960s.
