A new report from Europe raises serious alarms about orbital collisions

Starting with the pessimists: A few years ago, one of the world’s experts in orbital debris, University of Texas at Austin professor Moriba Jah, told Ars that he worries a lot about the consequences of satellites and debris in low-Earth orbit. “I think we are going to lose the ability to use certain orbits because the carrying capacity is going to get saturated by objects and junk,” Jah said. ” I also predict that we will see a loss of human life by (1) school bus-sized objects reentering and surviving reentry and hitting a populated area, or (2) people riding on this wave of civil and commercial astronauts basically having their vehicle getting scwhacked by an unpredicted piece of junk. I predict that both those things are going to happen in the next decade.” At the other end of the spectrum is the person almost solely responsible for the remarkable growth in satellites over the last decade, SpaceX founder Elon Musk. His attitude has largely been that space is big, and things will probably be just fine. For example, during a SpaceX-produced interview this summer at the company’s Starlink terminal factory in Bastrop, Texas, Musk said, “Space is really big. It’s not like space is gonna get crowded. Space is enormous. If you actually look at it relative to the Earth, the satellites are so tiny you can’t even see them.” So in one way of thinking, very, very bad things are coming. In another, everything’s fine. Where does the truth actually lie? Fortunately, it just released its annual Space Environment Report a week ago. The European agency has produced such a report over the last decade to provide a transparent overview of global space activities and assess the quality of efforts to preserve the sustainability of spaceflight. There are some striking—and concerning—changes this year. For example, the European report has dramatically increased its projections of future satellites in this year’s report after reassessing the current trajectory of large constellations. “The notable increase in the index this year is primarily driven by the substantially larger future population resulting from the current extrapolation scenario,” the report states. “In particular, the growing influence of large constellations highlights the limitations of traditional mitigation approaches when applied to future traffic at unprecedented scales. At the same time, the results are affected by the limited availability of detailed and verifiable information on future deployment plans, operational practices, and end-of-life strategies of these systems.” In its technically precise language, the European Space Agency is essentially saying we’re on a road that could ultimately lead to something like the Kessler syndrome. Such a scenario, with a dramatic growth in constellations using best practices for satellite disposal, looks like this in terms of collisions in orbit. So it’s clear that SpaceX is not operating its Starlink constellation in a cavalier manner. But it’s also clear that the company’s constellation, and those like it, are cause for significant concern going forward. No credible experts are saying that the Kessler syndrome could happen imminently—a single collision won’t set off a Gravity-style cascade. But space is getting more crowded, and some orbits, particularly from 520 km to 1,000 km above Earth. A 2025 paper by Hugh Lewis and Kessler (yes, that Kessler) found that some orbital bands in this region have already reached what is known as a “collisional-runaway threshold,” which is to say that any serious collisions there may create new debris faster over time than debris would be naturally removed by the pull of gravity, down into Earth’s atmosphere. Another concern comes from spent “rocket bodies,” upper stages from rockets that were not properly disposed of after launch. This was more common in decades past, but some launches today still do not reserve enough propellant to properly deorbit a second or third stage. These school bus-sized stages are particularly problematic at altitudes of 840 and 975 km, said LeoLabs space debris expert Darren McKnight. They are winging around uncontrolled, of course. And the higher the altitude, the longer the debris hangs around, from decades to centuries. Finally, because there is so much stuff flying around orbit, it would be relatively easy for bad actors to start shooting missiles at satellites in low-Earth orbit, creating debris fields that could potentially wipe out communications and cause massive financial damage. The probability of Kessler syndrome becomes much higher if humans start deliberately blowing things up in space. Did we mention that Iran recently became the ninth country to put a domestically built satellite into orbit? In the near term, it seems unlikely that space will become unusable. But it will likely become more and more expensive to operate there when considering avoidance technology, people to manage all of this, and propellant for maneuvers. And finding launch windows that avoid known debris will become more difficult. Longer term, perhaps as early as 15 years from now but more likely longer, a Kessler-syndrome type outcome may start to become increasingly plausible.