On this day in 1961, the X-15 rocket plane achieved a world record speed of 4,093 mph (Mach 6.04) and reached 101,600 feet (30,970 m or over 19 miles) altitude, piloted by U.S.Air Force Major Robert M. White. Its internal structure of titanium was covered with a skin of Inconel X, a chrome-nickel alloy. To save fuel, the X-15 was air launched from a B-52 aircraft at about 45,000 ft.
Test flights between 8 Jun 1959 and 24 Oct 1968 provided data on hypersonic air flow, aerodynamic heating, control at hypersonic speeds and piloting techniques for reentry used in the development of the Mercury, Gemini, and Apollo spaceflight programs. The X-15 reached 354,200 feet (107,960 m, 67 miles) on 22 Aug 1963 and Mach 6.7 on 3 Oct 1967.
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