Earth-orbiting satellites could begin colliding with one another in less than three days in a worst-case-scenario scenario — potentially triggering a runaway cascade that may render low Earth orbit (LEO) unusable, a new preprint study warns. This is 125 days quicker than if an emergency had happened just seven years ago, according to the researchers' newly devised "CRASH Clock."

The number of spacecraft orbiting our planet is rising fast, thanks largely to the rise of satellite "megaconsetllations," such as SpaceX's Starlink network. As of May 2025, there were at least 11,700 active satellites around Earth, most of which are located in LEO — the region of the atmosphere up to 1,200 miles (2,000 km) above Earth. For context, that is a 485% increase on the roughly 2,000 satellites in LEO at the end of 2018, before the first Starlink launch in 2019. And all signs suggest that this is only the beginning.