In 1978, NASA scientist Donald Kessler described a scenario where the density of objects in LEO becomes high enough that collisions generate debris faster than it can decay — creating a self-sustaining cascade.
In 1978, NASA scientist Donald Kessler described a scenario where the density of objects in LEO becomes high enough that collisions generate debris faster than it can decay — creating a self-sustaining cascade. The question today isn't whether it's possible, but whether certain altitude bands are already approaching it.
The mechanism is straightforward: more objects → more collisions → more fragments → even more collisions. The feedback loop becomes self-sustaining when the collision rate exceeds the natural decay rate.
Only the largest objects are individually tracked. The 1–10 cm population is the most dangerous: too small to reliably track but large enough to destroy a satellite on impact.
Kessler risk isn't uniform — it's concentrated in the most congested altitude bands.
Kessler syndrome means space becomes impassable overnight
It's a slow cascade over decades. Certain altitude bands could become unusable for satellites, but LEO as a whole wouldn't become an impenetrable wall.
It hasn't started yet
Some models suggest the 750–900 km band may already be in a very slow cascade. The debris population there grows even without new launches.
The solution is two-fold: prevent new debris (deorbit guidelines, passivation) and eventually remove existing debris (active debris removal). Time matters — the longer we wait, the harder it gets.