In less than a decade, the number of satellites in space has tripled: there are currently some 13,000 active probes orbiting Earth, according to data from the European Space Agency (ESA), as well as 40,000 other unmonitored objects. … larger than a Rubik’s cube (commonly known as space junk). This results in an increasingly crowded low orbit, in which satellites must constantly avoid each other (and space debris) to avoid collisions. And all because, in the event of an impact, thousands of pieces of metal would be generated, floating uncontrollably, which, in turn, could produce new collisions in a domino effect that would affect not only services such as communications or geolocation; but, in the worst case, they could lead us to remain locked on our own planet, without the possibility of sending rockets into space.
This nightmare has a name: Kessler syndrome. Theorized already in the 70s by the NASA consultant Donald J. Kessler, Some experts believe that we are getting closer, especially as megaconstellations like Starlink, to Elon Musk, They send thousands of new “tenants” into low orbit every year. And the forecasts don’t seem to improve if we take into account that soon other companies like Amazon or countries like China will soon launch their own networks in orbit.
To assess the risk of this scenario, Sarah Thiélé and their colleagues at the University of Priceton developed the CRASH Clock which, like the “Doomsday Clock”, which registers the threat of nuclear war to humanity, quantifies the risk of a cascade of collisions between satellites if they lose the ability to perform evasive maneuvers. And the result of the estimates, which has just been made public in a not yet peer-reviewed article, surprised the creators of the tool themselves: in the extreme case where the satellites could not be redirected, due to, for example, a solar storm or a power or communications outage or the fact that monitoring and space traffic management activities would not be carried out, the outlook would become dangerous in just 2.8 days.
“There is a considerable risk that ongoing or planned actions in orbit will cause serious degradation of the orbital environment or lead to catastrophic results.”
“There is considerable potential for ongoing or planned actions in orbit to cause severe degradation of the orbital environment or lead to catastrophic results, highlighting the urgent need to find better ways to quantify stress in the orbital environment,” the authors note. “Here we propose a new metric, the CRASH Clock, which measures this stress in terms of the time required for a catastrophic collision to occur if no collision avoidance maneuvers are performed or if there is a severe loss of situational awareness.”
However, these conclusions have sparked much debate within the scientific community and many experts criticize the alarmism that this work has produced in society.
From 121 days to 2.8 for the disaster
To have a prior baseline, the authors looked at the number of satellites orbiting Earth in 2018, before Starlink’s first launch – the megaconstellation began to be deployed from the following year. According to the CRASH Clock, at that time, with the number of satellites in orbit and if they had suddenly stopped being controlled from Earth, the first crash would have occurred in approximately 121 days.
However, since then, Musk has sent more than 9,000 probes into space which, when added to those sent by other agencies and companies, reduces the number of days to just 2.8. “This suggests that there is little time left to recover from a widespread disruptive event, such as a solar storm,” the authors note.
Very extreme event and study with “buts”
However, if many satellites were affected at the same time and could not reorient their trajectory, this would be an “extreme scenario”, as the researchers acknowledge. The greatest potential risk comes from solar storms, coronal mass ejections expelled by our Sun and whose visible consequence on Earth are the Northern Lights.
This phenomenon, which is harmless for life on Earth thanks to the action of our magnetic field – but not for electrical networks, which can suffer breakdowns due to charged particles from the Sun – can be much more dangerous in space. This can affect satellites in two ways.
On the one hand, solar radiation heats and expands the atmosphere and, with it, the resistance it generates on ships in low orbit. This forces them to consume more fuel to maintain their trajectory. As an example, a button: during the solar storm of May 2024 (where the auroras were visible even in Spain), more than half of the satellites in low orbit had to consume part of their fuel in these repositioning maneuvers. And in 2022 precisely, thanks to the probes of Musk’s constellation, 40 of the 49 satellites recently launched by SpaceX ended up reentering the atmosphere and disintegrating after an event with these characteristics.
Second, solar storms can literally destroy the electronic computing, navigation and communications systems of the satellites themselves. This would prevent them from maneuvering to avoid danger and could cause immediate damage, as the aforementioned study points out.
“The situation presented by the study is catastrophic”
Benjamin Bastida
ESA Space Debris Systems Engineer
However, the European Space Agency (ESA) calls for calm: it is not so simple that all satellites stop working at the same time because of a solar storm, these probes are preparing to orbit in these high-radiation environments and, moreover, the study has important limitations. “The situation that presents itself is catastrophic,” says Benjamín Bastida Virgili, space debris systems engineer at ESA. “Satellites are built to be able to withstand high levels of radiation. But even if we lose control of all the satellites for a few days, even in the busiest areas, the satellites of the large constellations are distributed in their orbits to naturally avoid collisions between them, and this is not taken into account in the article, where the risk is considered according to the density of the objects.
In other words, the CRASH Clock takes into account the number of satellites “by weight”, but not their trajectories, designed so that they do not collide with each other. “Also, even if there was a collision, there wouldn’t necessarily be an immediate cascading effect even if a fragment cloud was created that could cause further collisions,” Bastida says. However, the ESA engineer highlights the operational orbits in which the Starlink satellites move, “even if there were collisions in these orbits, after a relatively short time (15 years), the fragments would have returned and there would be no long-term problem.”
For his part, Alberto Águeda, Director of Space Traffic Monitoring and Management of the GMV company, emphasizes that, just as more and more satellites have been sent into space over the last decade, “during these years we have learned a lot and management capabilities have been developed.” “The study hypothesizes that an accident could occur in approximately three days if absolutely nothing was done, if the space was not monitored and if collision avoidance maneuvers were not carried out; But it is like a warning about the obviously numerous accidents that would occur on the roads if we drove without signs and with our eyes closed,” illustrates the expert.
He agrees with Bastida that the work encourages unnecessary social alarm because the scenario is “highly unlikely.” “Now it’s interesting from the point of view of the increase in the number of objects in orbit and the difference between the probability of collision in 2018 and in 2025, which has increased a lot.” Nevertheless, Águeda emphasizes that the monitoring of objects in orbit is increasingly precise and will continue to improve in the years to come. “We all want there to be balance in the orbit.”
Both emphasize that the article has not yet been peer-reviewed. “For this reason, the ESA considers that this method should not be used until it is validated, as it creates an alarmist situation far from reality. “Instead, ESA proposes a Space Environment Health Index that measures long-term developments and proposes capacity management with clear objectives.”
The truth is that the problem of low orbit saturation is one that concerns most space agencies and scientists around the world, who warn that the proliferation of satellites could pose a serious danger in the near future. However, there are already plans to reduce space debris and transform our orbit into a safer and more sustainable place for future generations.
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