It\u2019s been less than 70 years since humanity launched its first artificial satellite, Sputnik 1, into Earth\u2019s orbit. That event not only kicked off the Space Race but also the Space Age, our modern era of satellite infrastructure.\u00a0 <\/p>\n
By the start of 2019, there were around 2,000 active and dead satellite payloads in orbit around Earth. Today, there are over 17,000, with more than half of them operated by a single company: Starlink. Ten independent companies each plan to have over 1,000 satellites in low-Earth orbit (LEO) \u2014 the band of space below roughly 2,000 kilometers (1,240 miles) in altitude \u2014 in the near future, with the total number of planned satellites expected to exceed 700,000 by 2040. In January 2026, SpaceX submitted an application to put 1 million additional satellites into orbit as part of its push for orbital data centers, exceeding the cumulative total from all other providers combined.<\/p>\n
The most dire consequence of having so many satellites in LEO would be Kessler syndrome: a runaway chain reaction of collisions that renders the environment above our planet an impassable hazard zone. Scientists have already begun quantifying those risks \u2014 and outlining what it would take to reduce them.<\/p>\n
One collision after another<\/p>\n
While the benefits of satellite technology often appear right at our fingertips \u2014 from location and navigation services to messaging, streaming, and gaming apps \u2014 the risks are a little more subtle.\u00a0<\/p>\n
If LEO were home to just two satellites, and they happened to collide, the impact would destroy them both and create debris that might persist for a time, with most of it de-orbiting after a few centuries. However, if there are too many satellites in one \u201corbital shell\u201d \u2014 that is, within a particular orbital radius above Earth \u2014 a single initial strike could lead to many downstream strikes until potentially all of the satellites within that orbital shell are impacted. This would, in a worst-case scenario, create an impassable debris field around Earth. The environment of LEO would become an extreme collision risk to any spacecraft, crewed or uncrewed, that dared attempt to pass through it, possibly for thousands or even tens of thousands of years.<\/p>\n
This phenomenon \u2014 Kessler syndrome \u2014 was proposed as the stuff of science-fiction nightmares back in 1978 by Donald Kessler and Burton Cour-Palais, and it highlights the risks of overpopulating space in general, and LEO in particular: The greater the total mass of the satellites in LEO, the greater the risk of runaway Kessler syndrome becomes.\u00a0<\/p>\n
\u201cThe possibilities of collisions in orbit leading to Kessler syndrome \u2026 scares me deeply,\u201d says astronomer Samantha Lawler of the University of Regina in Saskatchewan.<\/p>\n
To help better quantify the risks of satellite collisions, Dr. Lawler, in collaboration with other astronomers, devised a new metric known as the Collision Realization and Significant Harm (CRASH) clock. By calculating how long it would take for a satellite collision to occur in the absence of collision avoidance maneuvers, the CRASH clock informs us of the dangers of our satellite infrastructure in LEO. Additionally, it helps us quantify the risks of succumbing to Kessler syndrome at present, particularly with a complete lack of meaningful mitigation measures.<\/p>\n
\u201cBigger satellites present bigger targets and thus have a higher collision probability, and if they do get hit, they will produce more debris than a smaller satellite,\u201d she explains. \u201cThe basic idea of the CRASH clock is: What if all the satellites in orbit experienced a catastrophic failure, how long would it take for a collision to occur? Right now, the CRASH clock metric says that we are likely to have a collision within 3.8 days.\u201d<\/p>\n
Rearranging the deck chairs<\/p>\n
If a satellite operator knows a collision is imminent, it can take action to prevent it. \u201cStarlink, the current biggest megaconstellation, executed one collision avoidance maneuver every 2 minutes on average between Dec. 2024 and Dec. 2025,\u201d says Dr. Lawler. But as more satellites continue to go up, the frequency of collision avoidance maneuvers will have to increase correspondingly \u2014 if we wind up with 1.7 million satellites in LEO, collisions would occur dozens of times each day barring successful avoidance maneuvers.<\/p>\n
Since satellites have finite sizes and response times, collision avoidance maneuvers are not enough to prevent all crashes, yet we have no other mitigations currently in place. According to the experts, we\u2019ve already passed the critical density of satellites to make Kessler syndrome a real risk. \u201cIf we stop launching new objects into orbit tomorrow, the rate of collisions in orbit will continue to increase,\u201d says Dr. Lawler. \u201cThat\u2019s the definition of Kessler syndrome, but right now the timescale between collisions is years. As we add more stuff in orbit, the timescale gets shorter and collisions become more likely.\u201d<\/p>\n
Every new satellite launch brings us one step closer to the worst kind of disaster: a completely avoidable one.<\/p>\n
Actively deorbiting every inactive satellite would lower the risk of Kessler syndrome, but it wouldn\u2019t solve the problem, and it would have its own major downside.<\/p>\n
Long before humans launched satellites, material from space was already raining down on Earth. Because planets are so massive, their gravitational forces constantly pull smaller objects \u2014 asteroids, micrometeoroids, space dust, cometary debris, etc. \u2014 toward them. This slightly decreases the total mass of objects in interplanetary space \u2014 the material and space between planets \u2014 while slightly increasing the masses of the planets themselves. It also decreases the number of stray bodies that can impact them in the future.\u00a0<\/p>\n
Earth draws in more than 12,000 tons of material annually, and almost all of it vaporizes and gets added to our atmosphere. However, the composition of that material is very different from the composition of the satellites burning up in the atmosphere.\u00a0<\/p>\n
\u201c[Meteoroids] are compositionally mostly rocks, while satellites are made of aluminum, carbon fibre, batteries, computers, solar panels, plastic, etc.: materials that do not normally get added to the upper atmosphere,\u201d Dr. Lawler relates. \u201cAnd most megaconstellation satellites are not small: the latest Starlink satellites, for example, weigh a ton each, and currently they are burning up one or two Starlinks per day. If they get to full operation, with 42,000 satellites each having five-year lifetimes, they\u2019ll be burning up nearly one satellite every hour.\u201d<\/p>\n
From a legal perspective, outer space is not considered an environment, so no one is assessing the environmental impact of adding these satellite components to our atmosphere. Whether we like it or not, we are currently undergoing an unplanned geoengineering experiment \u2014 one that ramps up significantly as we increase the number of satellites in LEO.<\/p>\n
A recipe for resilience<\/p>\n
One suggestion that\u2019s been made in the past is that any satellite constellation providers should be required to create \u201csafe parking orbits\u201d as protective measures in advance of any potentially adverse space weather event. While the satellite industry\u2019s party line is often to point to their shielding and an unwarranted confidence that their hardware would be immune to such events (which they demonstrably are not), choosing orbits that eliminate the risks of collisions remains a sadly underexplored option.\u00a0<\/p>\n
\u201cThe biggest improvements to orbital safety would come from dropping the density of satellites and debris in LEO,\u201d says Dr. Lawler when asked what solutions she would prefer. \u201cThis could be done by spreading out the orbits more. But even better would be limiting the number of satellites in orbit! This has the added benefit of also decreasing atmospheric pollution, ground casualty risks, and light pollution.\u201d<\/p>\n
However, without any pressure on satellite operators \u2014 save for that of stakeholders \u2014 to comply with these requests, many fear that calls for responsible planning will continue to fall on deaf ears. Scientists are watching the number and total mass of satellites in LEO increase without bound, and many expect it will continue to do so until the inevitable occurs: a collision that kicks off a disastrous chain reaction, triggering Kessler syndrome. The peak of the next solar cycle, in the mid-2030s, represents the most dangerous time in history for this completely preventable natural disaster.<\/p>\n
We have the know-how to be resilient against these adverse events and to prevent them before they occur. But until satellite providers adopt and implement these necessary mitigation measures, every new satellite launch brings us one step closer to the worst kind of disaster: a completely avoidable one, if only we had behaved responsibly up front.<\/p>\n