by Apostolos Christou

On the 11th of July 2021, we were informed that Virgin Galactic’s CEO Sir Richard Branson and his fellow passengers onboard VSS Unity reached “the edge of space”. But why “the edge” and not simply “space”, surely space is a well-defined domain so that one either reaches it or not? 

Actually, the definition of space is depends on who you ask. According to the Fédération Aéronautique Internationale (FAI, the body considered responsible for definitions regarding human spaceflight), the boundary between Earth’s atmosphere and “outer space” is the so-called “Karman line” at an altitude of 100 km (62 miles or 330,000ft). Branson’s ship reached a peak altitude of ~282,500 feet or 53.5 miles, therefore that flight did not qualify as a spaceflight under this definition. 

However, the United States government employs its own definition for human spaceflight, considering those who travel above an altitude of 50 miles (80 km or 264000 ft) to be astronauts. Under that definition, Branson and Co did become astronauts during Sunday’s flight. 

Under this same definition, the piloted X-15 rocket plane that flew between 1959 and 1968 reached space several times and many of its pilots received astronaut wings by the US Air Force. On two occasions, both with Capt Joseph A. Walker at the controls, the X-15 exceeded an altitude of 100 km and entered FAI-defined space.

On the 20th of July, the Blue Origin company’s “New Shepard” capsule will attempt to go above the 62-mi FAI boundary with passengers onboard, something that previous uncrewed test flights have already done. Blue Origin has stressed that outside the US, outer space is considered to begin at 100 km although, like Virgin Galactic’s Unity flight, the BO attempt will also launch from US soil.


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