Vertical boundary[edit]
There is no international agreement on the vertical extent of sovereign airspace,[citation needed] with suggestions ranging from about 30 km (19 mi)—the extent of the highest aircraft and balloons—to about 160 km (100 mi)—approximately the lowest extent of short-term stable orbits. (The satellite Lixing-1 had a stable orbit with an apogee of 140 km (87 mi) for three days.)[6] The Fédération Aéronautique Internationale has established the Kármán line—at an altitude of 100 km (62 mi)—as the boundary between the Earth's atmosphere and outer space,[7] while the United States considers anyone who has flown above 80 kilometres (50 mi) to be an astronaut[citation needed]. Indeed, descending Space Shuttles flew closer than 80 km (50 mi) over other nations, such as Canada, without requesting permission first.[8] Nonetheless, both the Kármán line and the U.S. definition are merely working benchmarks, without any real legal authority over matters of national sovereignty.
The boundary between public airspace and private air rights is defined by national or local law.
In the United States, the 1946 Supreme Court decision United States v. Causby overturned the common law doctrine that private property rights extend indefinitely upwards, instead ruling that they end 300 feet above the highest terrain (including buildings), the lower limit of the "public highway" defined by Congress in the Air Commerce Act of 1926. The Federal Aviation Administration regulates the construction and marking of structures taller than 200 feet near airports and 500 feet generally.[9]
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