— Ch. 1 · Defining The Edge Of Space —
Kármán line.
~3 min read · Ch. 1 of 6
The Fédération aéronautique internationale established a boundary at 100 kilometers above mean sea level in the 1960s. This specific altitude serves as the Kármán line for international record-keeping purposes. It distinguishes between aeronautical flight and astronautical travel under current regulations. No physical wall exists at this height to mark where air ends and space begins. Experts agree that atmospheric characteristics change gradually rather than abruptly. The FAI definition remains widely accepted by most international organizations including the United Nations. Some countries maintain different standards for their own legal or military applications.
Theoretical Origins And Calculations
Theodore von Kármán presented a paper on aerothermal limits to flight in 1956 at Berkeley, California. He calculated speeds and altitudes where continuous flight became possible without overheating due to friction. His chart showed an inflection point around 100 kilometers above which minimum speed would place a vehicle into orbit. Von Kármán noted that at 300,000 feet, centrifugal force dominates over lift forces entirely. Andrew G. Haley later invented the term "Kármán line" in a 1959 paper based on these calculations. Haley acknowledged the limit was theoretical and dependent on current aircraft technology like the Bell X-2. The original calculation relied heavily on heat-resistant materials available during the mid-twentieth century.