Sixty-one years ago today (19th July), Joe Walker officially became an astronaut, flying the X-15 experimental rocket-powered plane to an altitude of 106.1km (65.9 miles) above the Earth.
Although nominally an aircraft, as a consequence of its intended role pushing the envelope, it had some features that were highly unusual for a plane. The very blunt wedge shape of its tail made it difficult to control at low speeds, but was ideal for controlling the aircraft in the high atmosphere at Mach 6. It also had to include an RCS (reaction control system) to allow it to manoeuvre when there was insufficient air pressure.
Much of the X-15 was made from various aluminium alloys for its great strength-to-weight ratio, but due to its specialised nature key sections of the fuselage had to be constructed of heat-resistant nickel alloys. These are widely used in aeroplanes and space applications where vital components must retain their strength at high temperatures.
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