If waste disposal is a major environmental challenge across the world, rapid accumulation of junk in outer space is also a concern, going by the 2025 Space Environment Report from the European Space Agency (ESA), based on data collected until the end of 2024. Our planet is surrounded by spacecraft carrying out important work to study our changing climate, deliver global communication and navigation services and help us answer important scientific questions. But some of their orbits are getting crowded and increasingly churning with deadly, fast-moving pieces of defunct satellites and rockets that threaten our future in space.
Since Earth’s orbital environment is a finite resource, satellites that remain in their operational orbit at the end of their mission are at risk of fragmenting into dangerous clouds of debris that linger in orbit for many years. The number and scale of commercial satellite constellations in certain low-Earth orbits continue to increase year over year. Within certain heavily populated altitude bands the density of active objects is now the same order of magnitude as space debris. Intact satellites or rocket bodies are now re-entering the Earth atmosphere on average more than three times a day. Yet not enough satellites leave heavily congested orbits at the end of their lives, creating a collision risk.
The year 2024 saw several major fragmentation events as well as many smaller ones, together adding thousands of new debris objects, underlining the need for prevention by implementing passivation and reduced orbit lifetime measures. The adherence to space debris mitigation standards is slowly improving over the years, especially in the commercial sector, but it is not enough to stop the increase of the number and amount of space debris. Even without any additional launches, the number of space debris would keep growing, because fragmentation events add new debris objects faster than debris can naturally re-enter the atmosphere. To prevent this runaway chain reaction, known as Kessler syndrome, from escalating and making certain orbits unusable, active debris removal is required.
About 40 000 objects are now tracked by space surveillance networks, of which about 11 000 are active payloads. However, the actual number of space debris objects larger than 1cm in size – large enough to be capable of causing catastrophic damage – is estimated to be over 1.2mn, with over 50,000 objects of those larger than 10cm. ESA’s debris modelling tool MASTER shows that in the low-Earth orbit range of around 550km altitude there is now the same order of magnitude of debris objects posing a threat as there are active satellites. These preferential altitude ranges for communication constellations show a clear peak in satellite concentration. However, compared to previous years, a significant chunk of the active payloads in constellations are flying significantly lower, with about a quarter now in the sub-500km altitude bands.
Due to several major fragmentation events, as well as several smaller ones in 2024, there has been a large increase in objects in one year, with at least over 3,000 tracked objects added. The significant effect of such events illustrates the importance of measures undertaken at the end of a satellite’s or launcher’s lifetime that reduce the risk of such events. This includes passivation techniques to ensure there is no fuel or battery charge left that can lead to explosions and safely removing satellites from important orbits.
There is a scientific consensus that even without any additional launches, the number of space debris would keep growing, due to the Kessler syndrome. This chain reaction can make certain orbits become unsafe and unusable over time as debris continues to collide and fragment again and again, creating a cascading effect. This means that not adding new debris is no longer enough: the space debris environment has to be actively cleaned up.
