Earth-Space Boundary: Where The Earth End And Space Start? What Is Kármán Line?

Human space exploration has started with new point in 2021. With this a decades-old debate has started, the issue is the boundary of earth and space. And the question is, from where does space begin? This question is important from the point of view of space. It is also important for the people on earth. Due to this, tension can arise between the countries.

As easy as it sounds to hear this question, it is as difficult task to find the answer. Today will try to find the answer to this question. First of all, let us tell you how this debate started again?

How The Decades-old Debate Started Again?

Richard Branson traveled to space on 11 July 2021. In the spacecraft of his company- Virgin Galactic. Earlier, Jeff Bezos travelled to space on 20 July 2021. But Branson got the lead. He went into space before Jeff Bezos. Bezos's company Blue Origin claimed that Branson did not go to space, he returned before the Kármán line (the boundary of space). On 20 July 2021, Jeff Bezos went to space in the spacecraft of his company Blue Origin and crossed that boundary and returned back to Earth.

Due to the mutual disputes between these companies, this debate has again gained momentum that where is the boundary of earth and space? As Jeff Bezos claimed that Branson hasn't crossed the Kármán line. That's why technically he didn't reach the space. So first we try to understand what is this Kármán line? And how is the Earth-Space boundary defined?

How Is The Earth-Space boundary Defined? Difficulties While definining Earth And Space Boundary

There is no single opinion in the world on, where space begins? Different countries and different organizations define different boundaries. But all these countries and organisations agree on one definition. That is, space begins from where the Earth's atmosphere ends. Now the problem is that the Earth's atmosphere does not suddenly end at one place, it gradually disappears.

Earth's atmosphere is made up of many gases. Like everything else, gravity keeps these gases attached to the Earth. The higher we go above sea level, the weaker the gravity becomes. Therefore, gradually the air starts thinning at high altitude, because the amount of these gases starts decreasing.

At an altitude of 32 km above sea level, 99% of the atmosphere's air is present. The rest 1% air is between 32 km and 1000 km. If we decide such a boundary, where not a single particle of air is present, it will be close to 1000 km. But it is not possible to do this practically.

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The International Space Station orbits at an altitude of about 400 km above sea level. The Hubble Space Telescope is at an altitude of 500 km. Many satellites are orbiting below this 1000 km boundary. Therefore, if this 1000 km altitude is called the boundary of space, then all these will become aircraft instead of satellites. And then there will be a lot of trouble. 

The International Space Station orbits at an altitude of about 400 km above sea level. In this way, we will not be able to set any boundary of earth and space? In such a situation, there is a solution for this. Internationally line has decided the name of this line is the Kármán line.

Kármán Line

There is an international organization named FAI i.e. 'Fédération Aéronautique Internationale'. This organization sets the standards of human spaceflight. According to them, space starts about 100 kilometers above sea level. They decided an imaginary line, this imaginary line is called the Kármán line. Most of the countries consider this Kármán line as the boundary of earth and space. 

How Kármán Line Defined?

The Kármán Line is named after Theodore von Kármán. Theodore von Kármán was a physicist and aerospace engineer. In 1957, he tried to find out the limit above which no aircraft could fly.

Airplanes fly with the help of wind, in physics it is called aerodynamic lift. As mentioned earlier, the air becomes thinner with increase in altitude above sea level. At a certain altitude, the air becomes so thin that it becomes difficult for an aircraft to fly there. Von Kármán tried to calculate this height with the help of mathematics this imaginary boundary is called the Kármán line.

Most scientists agree that the Kármán Line can be considered the beginning of space. But there is no consensus on where the Kármán line will be.

Issues Against Kármán Line

In 1960, the FAI fixed the height of the Kármán line to 100 km, but it was a controversial decision. According to experts, the FAI fixed the height of the Kármán line by advocacy instead of science. Von Kármán himself measured the limit of 83.5 km from his calculation.

In the 1960s, the space race between the US and Soviet Union was at its peak. Then the delegations of America and Soviet Union agreed on the agreement that it would be right to make 100 km space limit. The value of this 100 km was not calculated with the help of any mathematics. Rather it was chosen so that it is easy for people to remember.

In 2018, a paper was published at the Harvard-Smithsonian Center for Astrophysics. The name of the astrophysicist who published this paper is Jonathan Christopher McDowell. According to him, 100 km was chosen because it is a good round figure. But here it has to be seen from the point of view of physical science. McDowell studied the different layers of the atmosphere and came to the conclusion that the more accurate value of the space boundary would be 80 km.

American institutions such as the Federal Aviation Administration, the US Air Force, NOAA and NASA generally consider 80 kilometers above the  sea level as the boundary of space. The US Air Force gives the title of Astronaut Wings to those who go above it. Richard Branson had returned after touching 85 kilometres. Therefore, according to them, they will be called astronauts but not as per FAI's definition of Kármán Line.

What If There Will Country Wise Space Boundaries?

In 1967 an international treaty on space was made named as Outer Space Treaty. Accordingly, the space is open to everyone. Every country can move freely in any part of space.

Now suppose, America and China consider different boundaries of space. America considers 80 kilometers and China considers 100 km. America will fly a vehicle at an altitude of 90 kilometers from the Chinese land, according to them, it will be in space. But according to China, that vehicle will be in their airspace. America will call a spaceship, China will call it an aircraft.

There is a hitch here, the space is open to all people, but this exemption is not for airspace. Every country has its own airspace, if an aircraft of another country enters there without permission, then it will be considered a threat. 

In order not to get trapped in such a case, it is necessary that the scientists of all the countries sit together and decide the final boundary.