Space: The New Frontier
From a technical perspective, atmospheres have no “end”; they just get progressively thinner. During the 1950s, it was generally known in the scientific community that, beyond some altitude, the physics of flight changed drastically. The principles for flight in the atmosphere, or the science of aeronautics, were fairly well understood. The principles for flight without an atmosphere, or the science of astronautics, were less understood. Some believed that these two disciplines needed some definition as to their separation.
There is no “bright line” that determines where outer space begins. NASA accords astronaut status to any individual who travels above 80 kilometers (50 miles). Yet atmospheric drag becomes evident on reentry at 75 miles above the earth’s surface.
The venerable Federation Aeronautique Internationale,8 which was founded in 1905, has ever since that time been accepted worldwide as the arbiter of aeronautical records. Through this private organization, the physicist Theodore von Karman in 1957 proposed a formula for the calculation of a boundary that would establish the beginning of space. One of the characteristics of aeronautical flight is the concept of lift, which is a function of speed through the atmosphere, among other things. The thinner the atmosphere, the faster the airplane must fly in order to gain the lift necessary to remain aloft. Karman proposed an altitude of approximately (the exact altitude depends on certain variables) 100 kilometers (62.1 miles) as the separation point based on his calculations that a space vehicle would have to travel faster than the speed necessary to obtain orbital velocity in order to maintain aeronautical lift. In other words, aerodynamic lift becomes less than centrifugal force.
This became the internationally accepted boundary to space, and it is known as the “Karman line.” The Federation Aeronautique Internationale is now the recognized keeper of all records that are established in astronautics.