With advancements in technology and a growing interest in space exploration, defining the boundary between Earth and space has become essential. The Kármán line is one of the most recognized scientific bases for this boundary, shedding light on the divide between Earth’s atmosphere and outer space.
This article delves into the boundaries of space by analyzing the Kármán line, its impact, history, scientific and legal dimensions, and the scientific and technical challenges in defining it.
What is the Kármán Line?
The Kármán line is an imaginary boundary that separates Earth’s atmosphere from outer space, located 100 kilometers above Earth’s surface. This line is based on physical reality, marking the altitude where conventional aircraft can no longer effectively fly due to the change in the physical laws governing flight.
Although the atmosphere extends above the Kármán line, the air becomes exceedingly thin at these high altitudes. Therefore, anything traveling above this line requires a propulsion system that does not rely on the lift generated by Earth’s atmosphere.
The History of the Kármán Line and the Evolution of the Earth-Space Boundary Concept
Determining the exact point where space begins is challenging because Earth’s atmosphere does not end abruptly but becomes thinner at higher altitudes, meaning there is no precise upper boundary.
Theodore von Kármán, an engineer, physicist, and spaceflight pioneer, proposed that the most logical edge of space would be where orbital forces exceed aerodynamic forces, determining that 100 kilometers was a good boundary.
Although von Kármán’s name is now associated with this space boundary, he never published this idea himself. His original work was a result of a discussion at a conference, and Andrew Gallagher Haley, the world’s first space law practitioner, published the first comprehensive study on space boundaries in the early 1960s.
He applied von Kármán’s criteria more specifically, defining the actual boundary of space as about 84 kilometers above Earth’s surface.
The international community, including the Fédération Aéronautique Internationale (FAI), considers space to begin at the Kármán line, or 100 kilometers, whereas NASA defines space as starting at about 80 kilometers.
Legal and Scientific Dimensions of the Kármán Line and Its Impact on Space Exploration
According to international law, the Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space states that “outer space shall be free for exploration and use by all.” Given the different definitions of where space actually begins, this could lead to various legal consequences.
Air traffic is generally regulated internationally, with nations controlling the airspace above their territories. Crossing this can inadvertently cause international conflicts. Thus, distinguishing between Earth’s airspace and outer space is of great importance, as space is for everyone, while airspace belongs to individual nations.
Defining the Kármán line as the invisible boundary where space begins is significant for space travel.
Even if the exact altitude where space starts is debated, the concept of defining this line helps in identifying whether something is in space or within Earth’s atmosphere. This also applies to defining astronauts, who only receive their astronaut licenses if they fly above this line.
Why Doesn’t Space Begin Where the Atmosphere Ends?
According to Space.com, some people wonder if it would be easier to define space as the point where Earth’s atmosphere ends. However, this definition would complicate matters further.
Traveling beyond the atmosphere would take us to about 10,000 kilometers above Earth’s surface to the outermost layer of the atmosphere, the exosphere.
The International Space Station orbits Earth at around 400 kilometers, and satellites orbit at about 1,000 kilometers. With space’s boundary at this new height of 10,000 kilometers, spacecraft and satellites orbiting Earth would no longer be considered spacecraft, and visitors to the ISS would not be called astronauts.
Therefore, the best options for the beginning of space are 80 kilometers or 100 kilometers at the Kármán line.
Scientific and Technical Challenges in Defining the Boundary Between Earth and Space
Jonathan McDowell, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics, told Popular Science that some scientists have suggested other criteria to define the boundary between Earth and space, such as the region in our planet’s orbit where a satellite breaks up upon reentry, which is around 80 to 90 kilometers above Earth’s surface.
NASA’s mission control center takes a different approach to defining the start of space. Instead of focusing on aerodynamic lift, NASA defines the return point to Earth’s atmosphere from outer space as the point where atmospheric drag becomes noticeable, about 122 kilometers up.
McDowell suggests that there are other boundaries some might consider for the edge of space. One is the Armstrong limit, named after American aerospace medicine pioneer Harry G. Armstrong, which is the altitude where human blood boils if not protected by a pressure suit due to low atmospheric pressure.
Considering the Kármán line as the boundary between Earth and space, this concept remains a cornerstone in our ongoing exploration of the universe around us. It is not just a technical line but encompasses scientific and technical challenges, posing legal and ethical questions about space use and exploration.
As technology advances and interest in space increases, our understanding of the Kármán line and its impact on our lives and the world around us becomes more significant. It presents an ongoing challenge for researchers, engineers, and policymakers to explore deeper into space and understand it better despite the challenges in defining these boundaries.
Author: Osama Al-Khader, Geography Teacher at Masarat Initiative
