カーマン・ライン
There is no international agreement on the vertical extent of sovereign airspace, with suggestions ranging from about —the extent of the highest aircraft and balloons—to about —the lowest extent of short-term stable orbits. The Fédération Aéronautique Internationale has established the Kármán line—at an altitude of —as the boundary between the Earth's atmosphere and outer space, while the United States considers anyone who has flown above to be an astronaut. Indeed, descending Space Shuttles flew closer than over other nations, such as Canada, without requesting permission first. Nonetheless, both the Kármán line and the U.S. definition are merely working benchmarks, without any real legal authority over matters of national sovereignty.