Joe Walker could be one of the greatest astronauts you have never heard of.

On 22 August 1963, Walker strapped into the cockpit of an X-15 experimental rocket plane for his final flight. He took off into the clear skies above Edwards Air Force base in southern California, his needle-shaped aircraft strapped beneath the starboard wing of a B-52 bomber.

At around 50,000ft, the X-15 dropped from the wing, Walker lit his engine and rocketed into the sky. When the plane ran out of fuel two minutes later, he was travelling at 5,600ft-per-second and the sky had turned from blue to black.

In another two minutes, Walker had reached 354,200 feet – 67 miles – above the Earth and beyond the air we breathe. He was no longer flying a plane but a spacecraft. 11 minutes and eight seconds after release, he was back on the ground – having glided at hypersonic speeds to a perfect landing on a dried-up lake bed.