Satellites Used to Have Months to Avoid CollisionsNow They Have Days

"The space around Earth has become increasingly cluttered with decades of accumulated debris left over from rocket launches, derelict satellites and the occasional antisatellite weapon testnot to mention growing mega constellations of thousands of active satellites. This influx of traffic means satellite operators have a fast-shrinking window of time to avoid a catastrophic collision in an emergency. While we had many months in the past, we now have less than a week for a close passage of serious concern"

"A new Collision Realization and Significant Harm (CRASH) Clock measure, described by Boley and his colleagues in a preprint posted to the server arXiv.org, shows how the rise of mega constellations has created an orbital house of cards. The clock uses statistics to estimate how long spacecraft now have to avoid a dangerous close pass or a collision, Boley says."

"The researchers' latest, unpublished calculations suggest that the CRASH clock value stood at about 5.5 days as of June 2025, compared with 164 days back in January 2018. The clock suggests the average satellite in low-Earth orbit currently faces a 17 percent chance of a close approach that could lead to a collision within 24 hours, which means satellites must make more frequent evasive maneuvers than they used to."

Low-Earth orbit has become increasingly cluttered with decades of debris, derelict satellites, antisatellite-test remnants, and thousands of new active satellites from mega constellations. Increased traffic has sharply reduced the available reaction time for satellite operators to avoid catastrophic collisions, dropping from about 164 days in January 2018 to roughly 5.5 days by June 2025. The CRASH Clock uses statistical measures to quantify how long spacecraft typically have to prevent dangerous close passes or collisions. Current conditions yield about a 17 percent chance that an average satellite will face a close-approach risk capable of causing a collision within 24 hours, requiring more frequent evasive maneuvers.

Read at www.scientificamerican.com