The CRASH Clock, Explained: How Close Satellites Really Are to Disaster

Five and a half days. That is the current answer to a question a small team of astrophysicists set out to measure precisely: if every satellite operator on Earth suddenly lost the ability to steer spacecraft out of each other's way, how long before the first catastrophic collision in low Earth orbit?

The number comes from a new metric called the CRASH Clock — Collision Realization and Significant Harm — introduced in a paper posted to the arXiv preprint server in December by Princeton graduate researcher Sarah Thiele and colleagues at the University of British Columbia and the University of Regina. It is not a claim that Kessler syndrome — the runaway cascade of orbital debris first described by NASA scientist Donald Kessler in 1978 — is 5.5 days away. It measures something narrower: how much error the system can currently absorb before something breaks.

"A lot of people are claiming we're saying Kessler syndrome is days away, and that's not what our work is saying," Thiele told IEEE Spectrum. "We're not making any claim about this being a runaway collisional cascade. We only look at the timescale to the first collision — we don't simulate secondary or tertiary collisions."

What is the CRASH Clock actually measuring?

The scenario is deliberately extreme: a solar storm, a software failure, or some other event knocks out every satellite's maneuvering ability at once. The CRASH Clock counts down from there. The team's first arXiv draft put the number at 2.8 days for June 2025 conditions, versus 121 days for 2018, before megaconstellations filled low Earth orbit. After other researchers weighed in publicly on the preprint, the team revised its methodology.

"The newer numbers are 164 days for 2018 and 5.5 days for 2025," Thiele said. "The paper is submitted and will hopefully go through peer review."

"If you think 5.5 days is okay when 2.8 days was not, you missed the point of the paper."

Samantha Lawler, University of Regina, co-author, speaking to IEEE Spectrum

Lawler, an astronomer and co-author, said the public correction process worked as intended. Putting the draft on arXiv with a note reading "feedback welcome," she said, drew responses from "top-tier experts" that improved the paper before formal peer review even began.

Why has the estimate dropped so much since 2018?

The short version: SpaceX's Starlink constellation has packed one of the most useful low-Earth-orbit altitudes, roughly 550 kilometers, far more densely than any operator has before. Lawler said Starlink's own conjunction report shows the constellation performing one collision-avoidance maneuver every two minutes on average. Every maneuver is proof the system still works — and proof of how little slack is left in it.

Aaron Boley, a University of British Columbia astronomy professor and co-author, cautioned against picturing a sudden chain reaction. "A lot of people's mental vision of Kessler syndrome is this very rapid runaway, and in reality this is something that can take decades to truly build," he said. What the CRASH Clock captures instead is stress on the system: as the number falls toward zero, operators have less room for the ordinary failure — a dead battery, a software glitch, an untracked fragment — that would have been survivable in 2018.

How does a solar storm actually trigger this?

Solar storms threaten satellites two ways, the researchers explained. They puff up the upper atmosphere, increasing drag and uncertainty about a satellite's exact position, and they can knock out the navigation and communication links operators need to dodge debris in the first place. During the May 2024 "Gannon" storm, Lawler said, position uncertainties reached kilometers for objects moving at roughly 7 kilometers per second — margins thin enough that, as she put it, everything is maneuvering at the same time, which adds uncertainty. Forecasters typically get only a day or two of warning before a major storm arrives.

None of this means low Earth orbit goes dark the moment a collision happens at a busy shell like 550 kilometers. "It would not become unusable — not a Gravity movie scenario," Thiele said. Operators would simply fly through a debris field for a few years, running more avoidance maneuvers, until atmospheric drag pulled the fragments back down.

The practical effect, for anyone who depends on GPS, weather data or a Starlink connection, has less to do with imminent catastrophe than with a rising bill: more maneuvers, more replacement launches, more fuel burned dodging junk that used to be rare enough to ignore. That is the price of treating a crowded sky as an unlimited resource, and the CRASH Clock is one of the first attempts to put a number on how little margin is left to keep paying it — a number its own authors keep revising upward as they check their work in public.

Space isn't the only place where the sun's unpredictability is quietly rewriting the rules this year. Daybreak Wire has also covered how the fading Solar Cycle 25 is still producing auroras well past its expected peak — a reminder that the same solar activity keeping the CRASH Clock a moving target also lights up the sky it threatens.