Satellites used to have months to avoid collisions, but now they have days
In the era of giant constellations, spacecraft typically have less than a week to avoid accidents.
The space around Earth has become increasingly cluttered by decades of accumulated debris left over from rocket launches, abandoned satellites, and the occasional antisatellite weapons test – not to mention a growing mega constellation of thousands of active satellites. This flow of traffic means satellite operators have a rapidly decreasing window of time to avoid catastrophic collisions in the event of an emergency.
“Whereas we previously had several months, we now have less than a week to get close to serious concern – possibly a major collision,” says Aaron saidAn astronomer at the University of British Columbia.
New one “Collision Sense and Critical Damage (Crash) Watch” SolutionDescribed by Bole and his colleagues in a preprint posted on the arXiv.org server, it shows how the rise of mega-constellations has created an “orbital house of cards.” Bole says the clock uses data to estimate how long it will take for the spacecraft to avoid a dangerous close approach or collision.
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The response window has decreased significantly since the satellite mega constellation took off with the launch of SpaceX’s first Starlink satellites in 2019. The researchers’ latest, unpublished calculations show that the CRASH clock value was about 5.5 days until June 2025, compared to 164 days earlier in January 2018. The watch shows that the average satellite in low-Earth orbit currently faces a 17 percent chance of a close approach that could lead to further damage. The collision within 24 hours, meaning satellites will have to take evasive maneuvers more often than before.
“As a concept, the crash clock is powerful because it turns ‘space getting crowded’ into a time-based metric that people can understand,” says Aaron Rosengrena mechanical and aerospace engineer at the University of California, San Diego, who was not involved in the study. “The exact numbers matter less than the trends.”
The calculations look at the current orbits of all listed objects and make simplifying assumptions about factors such as satellite distribution in orbit. It does not account for different maneuvering policies or risk limitations among satellite operators.
The spacecraft may not always be able to act fast enough to avoid a crash, especially if software glitches or powerful solar storms intervene. In 2019 a European Space Agency science satellite had to Escape from SpaceX Starlink satellitePartly due to a “bug” in the communications system used between the agency and Starlink. Most recently, this month SpaceX described a near miss Between one of its Starlink vehicles and a newly launched Chinese satellite.
The risk of collisions and widespread buildup of space debris – described as the Kessler-Kaur-Palace syndrome – is only increasing as companies and governments launch more satellites into similar orbits. There are more than 9,000 Starlink satellites currently active, about two-thirds of all active satellites. Rivals like Amazon’s Project Kuiper and Chinese companies are also racing to build mega planetariums of their own. Future plans for orbital space mirrors and space data centers may further complicate the situation.
Rosengren says the challenge is to coordinate to avoid conflicts between so many independent organizations that use different tools to monitor space and do not all share information equally. “The biggest driver is simple arithmetic,” he adds. “More satellites in the same orbital band means closer approaches, and the screening and response workload increases much faster.”
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