Satellite constellations could create spiraling space debris

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.

Earth’s cluttered orbit

The past five years have seen a boom in commercial space activity. For the most part, it has been driven by companies building huge networks, or “constellations,” of satellites to deliver internet access and other services worldwide. As these networks expand further, regulators have already received applications for well over a million more satellites.

But as Earth’s orbit becomes increasingly cluttered, there is mounting concern over satellites colliding with each other. Each time this happens, satellites can shatter into thousands of fragments, each capable of destroying further satellites.

Without tighter regulations, this problem could pose a serious risk to many of the satellite operations we depend on, from navigation to weather forecasting.

So far, however, most safety assessments have considered only the risk posed by a single satellite at a time. This entirely neglects the combined danger of constellations, which together would account for almost 1.7 million satellites if all current plans are approved.

Predicting constellation debris

To address this gap, Lewis built a straightforward mathematical model that tracks how often satellites and debris pass through a given point in space, accounting for how well satellites can steer away from collisions and how quickly they fall out of orbit once retired. Drawing on data from regulators and satellite trackers, he applied the model to 16 constellations: some still in their planning stages and others already in orbit.

Of these constellations, six exceeded the threshold beyond which debris grows unchecked—including large proposals from China and the U.S. Three more sat in an unstable zone, where junk accumulates without fully spiraling out of control.

This risk did not apply only to the largest constellations. In one constellation of just a few hundred satellites, instability emerged because of how its orbits were arranged. One fleet of tiny satellites tipped into runaway debris simply because they were too small to carry collision-avoidance thrusters.

Route to a safer orbit

Based on his calculations, Lewis suggests that many of these problems could be avoided with relatively modest design changes, such as boosting a satellite’s drag so it deorbits faster or extending its working life to cut the number of replacement launches.

With regulators still lacking clear, constellationwide standards, his method offers a practical way to spot risky proposals before launch and keep the paths above our heads clear for the satellites we depend on.

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