It's an arbitrary number, which is a good enough measure to distinguish an aircraft from a spacecraft. Kármán said that it's about this height where the aerody

It's an arbitrary number, which is a good enough measure to distinguish an aircraft from a spacecraft. Kármán said that it's about this height where the aerodynamic lift and inertia being dominant are reversed. https://en.wikipedia.org/wiki/K%C3%A1rm%C3%A1n_line https://en.wikipedia.org/wiki/K%C3%A1rm%C3%A1n_line