RU COSMOS 2600 and US FLOCK 4Q 27 were predicted to reach a closest approach of 8.54 km at 2026-10-28 08:27 UTC, at a relative speed of 3.44 km/s. Final forecast, made minutes before the pass. Best estimate after the pass, from the orbit data published nearest its time: 11.9 km at 28 Oct 08:27 UTC. One of the two changed orbit around the time of the pass (a maneuver or strong drag), so this estimate is less certain. This is a cross-border encounter between objects of different nations, the kind of event closely watched for space-security implications. Miss distance and time of closest approach are computed by propagating the latest published orbital elements for both objects, and each pass is re-checked every 20 minutes as new element sets are published. See the Satellite Maneuver Tracker for the live picture and space situational awareness for context.
The Two Objects
Where This Happens
At 331 km this pass sits in low Earth orbit. Objects here stay up for decades: there is too little atmospheric drag to clean the band naturally. Why crowded bands matter →
History Between This Pair
Repeat encounters are common for objects in near-intersecting orbital planes. Each pass is re-screened as fresh element sets arrive; "Final forecast" means the screening still predicted it within 45 minutes of its time, "Not re-confirmed" means later screening stopped finding it.
Forecast Record
How These Numbers Are Computed
Miss distance and TCA come from propagating the latest published orbital elements for both objects and searching for the minimum separation over the screening window. Element sets carry kilometre-scale uncertainty, so figures here describe a close pass, not a collision prediction; a change in either object's published elements re-computes the pass automatically. What is a conjunction? → How conjunction assessment works →