The Kessler Effect

For most of my working life I dealt with satellites in a very practical way. I ran INMARSAT’s nautical division. My mental map of space was orderly, predictable and frankly rather dull in the best possible sense. Coverage footprints, availability targets, GMDSS obligations. Space behaved itself.

Until recently, I had never heard of the Kessler effect (or Syndrome).

That omission makes sense once you understand the geography of orbit. Not all space is the same, and the risks are very unevenly distributed.

Start with GEO – geostationary orbit. This sits about 36,000 kilometres above the equator. A satellite up there takes 24 hours to circle the Earth, exactly matching the planet’s rotation. From the ground it appears fixed in the sky. That is why GEO is so valuable for communications and safety services. A handful of satellites can cover huge areas continuously. Everything in GEO moves at the same speed, in the same direction, in the same plane. Relative velocities are low. Collisions are rare. When satellites reach end of life they are boosted into a graveyard orbit a few hundred kilometres higher. It is orbital tidying, not orbital warfare.

That was my world.

Then there is LEO – low Earth orbit. This starts a few hundred kilometres up and extends to roughly 2,000 kilometres. Satellites here circle the Earth every 90 minutes or so. They are close, fast and numerous. Earth observation, weather forecasting, reconnaissance, the International Space Station and the new mega-constellations all live here. Objects in LEO travel at around 7 to 8 kilometres per second. Closing speeds can reach 15 km/s. At that velocity, a loose bolt is not debris, it is a weapon.

LEO is where the Kessler effect bites. Pack enough objects into the same orbital shells and collisions become inevitable. One smash creates thousands of fragments. Those fragments increase the odds of the next collision. Eventually the process sustains itself. Even if launches stopped, the debris would keep colliding for decades. Certain orbits would simply become unusable. This is not speculation. It is basic physics.

Between the two sits MEO – medium Earth orbit. Roughly 2,000 to 35,000 kilometres up. Fewer satellites, but some of the most important ones of all. GPS, Galileo and other navigation systems live here. MEO is less crowded than LEO, so collision cascades are unlikely, but there is a sting in the tail. Debris up there effectively lasts forever. A serious breakup in a navigation shell would not explode into a frenzy of impacts, but it would permanently degrade an orbit that modern civilisation quietly depends on.

There is also a comforting myth that satellites are simply “sent off into space” when they are finished. They are not. In LEO, responsible disposal means lowering the orbit so atmospheric drag burns the satellite up. That only works reliably at lower altitudes and only if the satellite is still controllable. In MEO and GEO, disposal means pushing the satellite into a higher parking orbit. It remains bound to Earth indefinitely. The rubbish does not go away, it is just moved aside.

Seen through this lens, the Kessler effect is not some abstract theory dreamt up by anxious scientists. It is the inevitable consequence of treating LEO as an infinite commons. We are launching hardware at industrial scale into the fastest, most crowded part of near-Earth space, with short design lives and weak incentives to clean up properly.

From a maritime safety perspective the irony is hard to miss. We would never tolerate an industry that abandoned wrecks across the busiest shipping lanes and shrugged because future captains could try to steer round them. Yet that is exactly what we are doing in low Earth orbit.

I spent years working in a part of space that was calm because it was regulated and inherently stable. Discovering the Kessler effect felt less like learning something new and more like realising that, somewhere below my old geostationary perch, we are quietly turning orbital space into the same sort of mess we have already made everywhere else.