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An image of the Karman Line indicating the edge of space

The Karman Line
Defining the Edge of Space

Astronautical.art is dedicated to art in the outer space environment. But what is Outer Space? And where does it begin?

According to the Cambridge Dictionary, Outer Space is "The universe beyond the earth's atmosphere". But then, where does earth's atmosphere end?

This seemingly trivial question is particularly hard to answer. In fact, nobody really knows. Despite decades of debate, there is no consensus on what constitutes the boundary between airspace and outer space, and the easiest solution to-date has been to not agree on a definition.


The atmosphere is the layer of gases that surrounds our planet and extends from the earth's surface up to as far as 10.000 km, gradually blending into the vacuum of space without a defined border. 

Within this region, 'Airspace' involves flight by aerostatics (balloons) or aerodynamic lifting (airplanes, helicopters) through earth's atmosphere, where 'Space' involves flight by rocket-powered vehicles whose flight paths are governed by ballistics and orbital mechanics operating in the absence of an atmosphere.

Currently, there exist five "Delimitations between Airspace and Space":


 

80 km

"Roughly the point at which aerodynamic control surfaces are no longer useful". This delimitation is used by the National Advisory Committee on Aeronautics (NACA), NASA and the US Military.


 

100 km

Karman Line

"A vehicle at this point would have to fly faster than orbital velocity to derive sufficient aerodynamic lift from the atmosphere to support itself". This boundary is set at '100km' for ease of use. It is the most common and internationally used boundary between airspace and space.


 

118 km

"The midpoint of gradual transition over tens of kilometres from relatively gentle winds of the Earth's atmosphere to more violent flows of charged particles in space. This delimitation is not functionally used by any organisation. 


 

122 km

The point of reentry at which atmospheric drag becomes noticeable. Used by NASA Mission Control.


 

129-150 km

"The lowest perigee attainable by an orbital space vehicle. 129 km is the lowest altitude at which an object in an elliptical orbit can complete at least one full revolution without propulsion, and 150 km is the lowest orbit at which an object in circular orbit can complete one full revolution". 

The Astronautical Art Initiative considers the generally accepted delimitation of

The Karman Line

as the Beginning of Space

Based on the excellent article "Where is Space? And Why Does That Matter?" by Bhavya Lal and Emily Nightingale, which can be found here.

Original image is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license by Kelvinsong. The original image can be found here.

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