Crash clock says satellites in orbit are three days from disaster

The collision would have occurred in just 2.8 days if all the satellites had lost the ability to evade each other, highlighting how crowded Earth's orbit is becoming.

Over the past seven years, the number of satellites has more than tripled. from 4000 to almost 14000. The main reason for this growth was Starlink constellation from SpaceXwhich now has more than 9,000 satellites in low Earth orbit at an altitude of 340 to 550 kilometers above the Earth.

This significant increase means the satellites must constantly avoid each other, known as a collision avoidance maneuver, to prevent accidents that could create thousands of pieces of metal and potentially render parts of Earth's orbit unusable.

According to the company's report, from December 1, 2024 to May 31, 2025, SpaceX completed 144,404 collision avoidance maneuvers, which is equivalent to one maneuver every 1.8 minutes across its entire constellation. There has only been one collision of satellites in orbit in history. In 2009, an operational Iridium Communications satellite collided with the defunct Russian Cosmos satellite. Hundreds of pieces of debris from this event are still orbiting the Earth.

Sarah Thiele from Princeton University and her colleagues used publicly available data on the location of satellites to model how their increase in number affected the risk of collision. They came up with a new metric called Collision Realization Hours of Significant Harm (CRASH) to quantify risk. The title draws comparisons to the infamous Doomsday Clock, which depicts the threat of nuclear war threatening humanity. “We definitely talked about it a lot,” says Samantha Lawler at the University of Regina in Canada, another team member.

They found that if all the satellites in orbit in 2018—before SpaceX's first Starlink launch in 2019—had suddenly lost the ability to maneuver, a collision would have occurred within 121 days. However, today this number is only 2.8 days due to the large number of satellites in orbit.

“We were shocked that it was so short,” Thiele says.

The 2.8-day figure suggests that some event, such as a powerful solar storm, rendered all satellites unable to change course. In May 2024, a severe solar storm caused some Starlink satellites to fail. ripple of a giant wave in response to an event. A repeat of the most powerful solar storm in history – the Carrington event of 1859 – could cause serious problems, although Wine Vattapalli SES Satellites in Luxembourg says it probably won't knock out all the satellites. “It’s unlikely that we’ll be able to take them all out at once,” he says.

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Scientists say a metric like CRASH Clock is useful for identifying how crowded Earth's orbit is becoming. Hugh Lewis at the University of Birmingham, UK. “Can we keep expanding this house of cards?” he says. “The more cards are added, the greater the collapse will be when something goes wrong.”

In the coming years, SpaceX, Amazon and several Chinese companies plan to launch tens of thousands more satellites for their own mega-constellations. This means that it is likely that the CRASH rate will decrease further, increasing the likelihood of collisions. “It’s scary to think about,” Thiele says.