What is Kessler syndrome?

It was proposed in 1978 and is currently of increasing concern to space agencies. Why?


Although it is not usually a regular topic of conversation, we rely on satellites for much of our daily lives. Thanks to them we have GPS, global communication and accurate weather reports. They also help measure the destruction of the environment, track climate or sea level. However, satellites that have become essential in our lives, face a big problem: the huge amount of space debris-which keeps growing and with which they share the low Earth orbit (LEO).

What happens when a satellite stops working or is no longer needed? They do not return to Earth or disappear in any way. When a satellite breaks down, no one goes up into space to fix it. They all stay there, stay in orbit, moving at incredible speeds. It’s hard to look at the sky, think of anything that might make space exploration difficult, but those dead satellites, paint stains, fragments of solar panels or rockets from ancient missions can pose a threat.

There are millions of pieces of debris in orbit and only a few tens of thousands are regularly tracked by the United States military. When thousands or even millions of objects are flying around our planet at tremendous speeds, the potential for collisions is high.

It was in 1978, when NASA astrophysicist Donald J. Kessler set out what scenario would await our skies as we launched satellites into space. His prediction was that debris in low Earth orbit would eventually reach a tipping point, and when that happened, it would start a collision chain reaction. Each collision would create even more space debris, which in turn would cause even more collisions and so on. This domino effect is what we know as Kessler’s Syndrome. Basically we would become prisoners on our own planet.

Although the army has the largest public space debris database, it does not include satellites omitted by international Governments, commercial companies or other ongoing projects.

All that space debris moves at speeds of up to 27,000 km per hour and each object varies in direction as it is affected by the Earth’s gravitational field. Avoiding collisions by evasive maneuvers consumes the satellite’s fuel and time, making it a less efficient instrument than it should be. There is also the detail that most objects in orbit cannot be controlled from Earth, so there is no way to interfere with debris on a collision course.

The danger of even a small fragment traveling at high speeds is easy to see. As calculated by NASA, a one centimetre "paint stain" traveling at 10 km/s can cause the same damage as a 250-kilogram object moving at about 100 km/hour on Earth. If we increase the size of the fragment to 10 centimetres, such a projectile would have the force of seven kilograms of TNT. If we imagine thousands of such objects flying at dizzying speeds and colliding with each other... the landscape is truly a nightmare.

With a chain reaction of collisions and space debris explosions, the orbital area would be filled with highly hazardous debris and the space programme would be endangered for all space agencies. Journeys beyond low Earth orbit, such as the planned mission to Mars, would become more challenging. Additionally, let’s remember that the largest object in low Earth orbit is the International Space Station (ISS) that hosts astronauts continuously. A major collision with the ISS would be disastrous.

To prevent major complications, it is imperative to create less debris and take measures to mitigate pollution in space: the number of satellites launched must be limited, there is a need to ensure that these objects can be safely disposed of once they are not needed and to seek a workable solution to sweep or clean up existing space debris.

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