X-15 number 56-6670 flew 81 missions, including the last eight of the program. It reached a speed of 4,104 mph (Mach 6.06), and an altitude of 266,500 feet. Eric Long/NASM Inconel X, a ferociously ...

The X-15 was a key bridge between conventional atmospheric flight and spaceflight. The North American X-15 is one of the most ...