Illustration Credit: NOIRLab/NSF/AURA/P. Marenfeld
By Jonathan O’Callaghan,
Published by New Scientist, 16 December 2025
Satellites in orbit would begin to collide in a matter of days if they lost manoeuvrability during a solar storm or other outage
A collision would occur in just 2.8 days if all satellites lost their ability to dodge each other, highlighting how crowded Earth’s orbit is becoming.
In the past seven years, the number of satellites has more than tripled from 4000 to nearly 14,000. The main cause of this growth has been SpaceX’s Starlink constellation, which now numbers more than 9000 satellites in low Earth orbit between 340 and 550 kilometres above Earth.
This large increase means satellites must constantly dodge out of the way of each other, known as a collision avoidance manoeuvre, to prevent crashes that would generate thousands of pieces of metal and potentially render parts of Earth’s orbit unusable.
From 1 December 2024 to 31 May 2025, SpaceX performed 144,404 collision avoidance manoeuvres, equivalent to one every 1.8 minutes across its constellation, according to a report by the company. Only one collision between satellites in orbit has ever occurred. In 2009, an active satellite run by Iridium Communications hit a defunct Russian Kosmos satellite. Hundreds of pieces of debris from the event still orbit Earth.
Sarah Thiele at Princeton University and her colleagues used public positional data of satellites to model how their increased number has affected the collision risk. They came up with a new metric, called the Collision Realization And Significant Harm (CRASH) Clock to quantify the risk. The name invites comparisons with the infamous Doomsday Clock that charts humanity’s threat of nuclear war. “We definitely talked about that a lot,” says Samantha Lawler at the University of Regina in Canada, another member of the team.
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