Define the boundary between the Earth’s atmosphere and space

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Recently, the space seems to have become much more commercial. While the 1967 Outer Space Treaty states that “the exploration and use of outer space must be carried out for the benefit and in the interest of all countries and must be owned by all countries. ‘humanity’, the situation is changing rapidly.

Billionaires are launching space tourism, private companies are positioning themselves for alien mining, others are planning space hotels and giant billboards in orbit.

As activity shifts from space exploration to space exploitation, we can expect more legislation to follow the Space Launches Competitiveness Act of 2015, a shift from public space programs to private companies that are moving forward. launch into space, and an increase in space-based feuds and disputes.

There is also the question of how far national sovereignty extends vertically. How far does American airspace go? How far do you have to go before an airplane becomes a spaceship and a pilot becomes an astronaut?

Ownership of vertical airspace

Private vertical airspace: Before the era of air travel, a maxim known as Ad Coelum meant that a landowner had an infinite column of air above his piece of land. Today, private airspace ends where navigable airspace begins, but it is poorly defined; somewhere between 80 and 500 feet above ground level. This has implications for intrusion from above and will likely become more contentious as the use of drones increases.

National vertical airspace: In terms of national sovereignty, there is currently no international agreement on the vertical extent of airspace. However, the Karman line is used as a working reference.

The Karman line

In an effort to define the boundary between Earth’s atmosphere and space, the International Aeronautical Federation (the World Air Sports Federation, or FAI) established the Karman Line in the 1960s, choosing a round, neat number: 100 km or 62 miles above the Earth average. sea ​​level. The FAI divides air activity into two: anything within 100 km of the earth’s surface is aeronautics, while anything beyond 100 km is aeronautics. of astronautics.

The Karman Line is recognized by several international organizations including the UN, but the international community still lacks a legal definition of the edge of space.

In the United States, NASA, the Air Force and the FAA consider space to begin 80 km above the surface. A person must reach this height (and meet other criteria) before they can be considered an astronaut and earn their astronaut wings.

What layer of Earth’s atmosphere does the Karman line belong to?

In reality, there is no sudden transition from atmosphere to space. On the contrary, there is a gradual thinning of the atmosphere through five layers.

1. The troposphere starts at sea level and stretches for 5 to 9 miles. 99% of atmospheric water vapor is found in this layer. Mount Everest reaches about 5.5 miles high, with the “death zone” (where the air is too thin to breathe safely) starting at about 5 miles.

2. The stratosphere extends from the top of the troposphere to about 31 miles above sea level. Commercial passenger jets fly in the lower stratosphere, which lacks turbulence relative to the troposphere. This layer includes the ozone layer. Some ISPs use stratospheric balloons and high altitude pseudo-satellites as an alternative to towers and satellites.

3. The mesosphere begins above the stratosphere and extends to about 53 miles above sea level. At this point, atmospheric pressure has fallen below 1% of the pressure at sea level. Most meteors burn in the mesosphere.

4. The thermosphere begins above the mesosphere and extends to about 372 miles. The International Space Station and most satellites orbit this layer, and this is also where the auroras occur. The Karman Line is located in the lower part of the thermosphere.

5. Almost – but not quite – a void, the exosphere extends from the top of the thermosphere to 6,200 miles and is the upper limit of the atmosphere.

To complicate matters slightly, another layer known as ionosphere overlaps the mesosphere and thermosphere, increasing and decreasing with the amount of solar radiation absorbed.

Crossing the Karman Line

With the United States, China, and Russia all pursuing anti-satellite weapon capabilities, strategists expect any future conflict between two or more major powers to include the downing of military and possibly civilian satellites. If the tensions were to escalate, vertical borders would start to matter a lot. In the future, “Crossing the Karman” may become the space-age equivalent of Crossing the Rubicon.

Image Credit: Dima Zel /

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