20km seems awfully low. The Kármán line at 100km [1] is what most would use. Alternatively 80km is also used. -- [1] https://en.wikipedia.org/wiki/K%C3%A1rm%C

20km seems awfully low. The Kármán line at 100km [1] is what most would use. Alternatively 80km is also used. -- [1] https://en.wikipedia.org/wiki/K%C3%A1rm%C3%A1n_line https://en.wikipedia.org/wiki/K%C3%A1rm%C3%A1n_line