To date, close to 30,000 satellites have been launched into Earth’s orbit, leading to mounting concerns over the debris created when they collide. In a new analysis posted to the preprint server arXiv, Hugh Lewis of the University of Birmingham shows that satellite constellations can grow so large that they cross a critical size beyond which they generate unstable, runaway amounts of debris. The findings point to an urgent need for tougher rules on which satellites are allowed into orbit in the first place.