The Kármán Line

The Kármán Line is the imaginary boundary between Earth’s atmosphere and outer space. The Fédération Aéronautique Internationale (FAI) defines it as being at an altitude of 100 km (62 miles) above sea level. When a vehicle crosses this altitude, it is generally considered to have reached space.

Why 100 km?

The concept was introduced by physicist and engineer Theodore von Kármán.

• At around 100 km altitude, the air becomes so thin that aerodynamic lift is no longer sufficient to support flight.

• Beyond this point, a craft can only move by using rocket propulsion, not by wings or normal aircraft engines.

That’s why 100 km is chosen as the practical boundary between atmosphere and space.

Different Definitions

• FAI (International Aeronautics Federation): 100 km.

• U.S. Air Force & NASA: Define the boundary at 80 km (50 miles). That’s why some astronauts have been awarded “astronaut wings” after crossing 80 km, even if they didn’t reach 100 km.

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Importance of the Kármán Line

• Airspace vs. outer space: Helps determine when national airspace ends and “international space” begins.

• Astronaut status: Crossing it is often the threshold for being recognized as an astronaut.

• Science & technology: Used as a reference in space tourism, satellite launches, orbital mechanics, and space law.