The Explorers' Club, № CMLXV

Operation AXIOM: The Space Race—The 60th Anniversary of X-15 Flight 90
19 July 1963: X-15 Flight 90 lifted off from California's Edwards Air Force Base, with Pilot Joe Walker aboard X-15-3 hoisted aloft by the NB-52 mothership Balls 8; Walker flew his rocketplane through a parabolic arc above the Kármán line, the internationally-recognized boundary of outer space, achieving an altitude of nearly sixty-six miles (65.9); X-15-3 landed on Rogers Dry Lake at Edwards.

Commentary: The U.S. Department of Defense defines the boundary of outer space—& thus anyone who flies above that line as an astronaut—at fifty miles above mean sea level (or eighty kilometers). Walker had previously earned his U.S. Air Force astronaut wings during X-15 Flight 77 on 17 January 1963, achieving an altitude of fifty-one & a half miles (51.5 miles, or 82.9 kilometers).

The Kármán line definition of one hundred kilometers (or sixty-two miles) above mean sea level is used by the Fédération Aéronautique Internationale, the international governing body for air sports. The U.S.'s Federal Aviation Administration, which regulates civilian space flights, such as suborbital flights by Blue Origin's New Shepard capsule or Virgin Galactic's SpaceShipTwo spaceplane, adheres to the international Kármán line definition of space.

Bonus! Space Race Song o' the Day: Flight 90
The Phenomenauts, "Fly through the Sky" from the Electric Sheep E.P. (Space Cadet Mike Papa Whiskey)

Semper exploro.