Satellite Conjunctions

25 hand-written examples (5 red, 6 orange, 8 yellow, 6 green) showing how conjunctions of each level read — object pairs, miss distances and probabilities modelled on real event classes such as the COSMOS 1408 debris field. Times are relative to when the scenarios were seeded. They do not describe real, current close approaches and are not counted in the headline figures.

What is a satellite conjunction?

A conjunction is a predicted close approach between two objects in orbit — two satellites, or a satellite and a piece of debris. Tracking networks propagate every catalogued object forward, and when two paths come within a screening volume (typically a few kilometres) a Conjunction Data Message (CDM) is issued describing the time of closest approach, the predicted miss distance and, where covariance allows, a collision probability.

What miss distance actually matters?

Miss distance alone is a poor guide because position uncertainty can be hundreds of metres to kilometres. Operators act on collision probability (Pc), which combines miss distance with the uncertainty of both objects. The widely used decision line is Pc of 1 in 10,000 (1e-4): above it most operators plan an avoidance maneuver; between 1e-5 and 1e-4 they watch and refine tracking. A 100 m miss with tight covariance can be safer than a 1 km miss with poor tracking.

Who maneuvers, and who decides?

Whichever object is active and maneuverable is expected to move — debris cannot. When both are active satellites, operators coordinate directly or through the 18th/19th Space Defense Squadron and commercial services; large constellations such as Starlink maneuver automatically when Pc exceeds their internal threshold. There is no binding right-of-way rule in orbit, which is why conjunction data being public matters.

Where do these rows come from?

The live table reads the public CDM class on Space-Track.org, the US Space Force catalogue service. SpaceNexus fetches CDMs created in the last seven days with a future time of closest approach every six hours. Space-Track requires a free account; if the fetch credentials are not configured the live table is empty and the page says so rather than showing stand-in data as real.