02. How was the distance from Earth to space decided? (A K2S Question)

From The Space Library

There is no real noticeable boundary, because the atmosphere gets thinner in a gradual way. The US Air Force decided to use 50 miles as the measurement point, which is about the height at which the ionosphere begins, and so they award pilots Astronaut Wings when they reach that altitude. The international people who keep altitude records decided to use 62 miles which is 100 kilometers, and so the X Prize organizers chose to use 62 miles as the target for their prize flights in 2004.

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Answer provided by Derek Webber

Question and Answer extracted from the book Kids to Space - by Lonnie Schorer

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