The Kármán line is a conventional boundary between Earth's atmosphere and outer space, set at 100 kilometers above mean sea level by the Fédération aéronautique internationale in the 1960s. The altitude is largely administrative rather than physical; the atmosphere thins gradually with no sharp edge. The FAI chose a round figure close to the altitude where aerodynamic lift can no longer sustain a vehicle in flight and centrifugal force must take over entirely.
Who calculated the original altitude for the Kármán line?
Theodore von Kármán calculated a theoretical aerodynamic limit of 83.8 km in a 1956 paper on aerothermal limits to flight, using the Bell X-2 as his reference aircraft. The term "Kármán line" was coined by lawyer Andrew G. Haley in a 1959 paper based on that work. The FAI later set its official definition at the rounder figure of 100 km.
Does the United States use the 100 km Kármán line definition?
The U.S. does not use the 100 km standard. The U.S. Armed Forces define an astronaut as anyone who has flown above 50 miles above mean sea level, and NASA changed its standard from 100 km to this 50-mile threshold in 2005 to avoid inconsistencies between military and civilian crew members on the same flights.
Which NASA X-15 pilots were retroactively awarded astronaut wings?
John B. McKay, William H. Dana, and Joseph Albert Walker were retroactively awarded astronaut wings after the U.S. threshold was lowered, because they had all flown between 90 km and 108 km during the 1960s without being recognized as astronauts at the time. Two of the three awards were given posthumously. Walker's highest flights exceeded 108 km, which is above even the FAI's 100 km standard.
What is the scientific case for setting the space boundary at 80 km instead of 100 km?
Research published in 2018 by Jonathan McDowell of the Harvard-Smithsonian Center for Astrophysics and Thomas Gangale of the University of Nebraska-Lincoln argued for 80 km on several grounds. Satellites with perigees below 80 km are highly unlikely to complete their next orbit, orbital objects can survive multiple perigee passes between 80 and 90 km, and meteors typically disintegrate in the 70-100 km altitude range.
What is the Kármán line for Mars and Venus?
Estimates vary by researcher. Isidoro Martínez calculated equivalent altitudes of 80 km for Mars and 250 km for Venus. Nicolas Bérend arrived at 113 km for Mars and 303 km for Venus. The higher figure for Venus reflects its thick, dense atmosphere, while the lower figure for Mars reflects its thin one.