Satellite Conjunction Watch
Thousands of satellites and pieces of debris share low Earth orbit, and every day some of them pass close to one another. These predicted close approaches are called conjunctions. This page shows the current week’s forecast from CelesTrak’s SOCRATES service: the encounters involving the ISS, China’s Tiangong station and the Hubble Space Telescope, followed by the closest approaches and the highest worst-case probabilities anywhere in orbit.
This week’s screening
Loading this week’s conjunctions…
Highest worst-case probability
Active spacecraft only, ranked by the maximum collision probability SOCRATES computes. Docked vehicles and pairs from the same mega-constellation are removed.
Closest approaches
The smallest predicted miss distances this week, with the same filters applied. Very small distances are common in this list for objects with uncertain orbits.
How to read these numbers
Time of closest approach (TCA) is the moment the two objects are nearest, shown in your local time. Miss distance is how far apart they are at that moment. Relative speed is how fast they are moving past each other: typically 7 to 15 kilometres per second, which is why even a small piece of debris is dangerous. Maximum probability is the highest collision probability consistent with the uncertainty in the orbit data. It rises when the data are poor, so a large figure often means “we are not sure” rather than “this is dangerous”.
SOCRATES screens every catalogued object pair over the coming week and reports every approach closer than a set threshold (shown above). Because it uses publicly available two-line orbital elements, accuracy is limited; satellite operators work from much more precise data supplied directly by space-surveillance networks.
What the ISS does about debris
The International Space Station can change its orbit when a close approach looks risky. Mission control generally considers an avoidance manoeuvre when the calculated probability of collision from precise tracking data is around 1 in 10,000 or higher, firing thrusters, usually on a docked spacecraft, for a few minutes to nudge the station’s orbit. These debris avoidance manoeuvres are occasional, not routine. When a threat is found too late to manoeuvre, the crew can instead shelter in their docked spacecraft as a precaution.
Why docked vehicles and constellations are filtered
A visiting spacecraft docked to the station travels with it, so the raw data show the two “meeting” every orbit at almost zero relative speed and a distance of metres. That is not an encounter, and listing it would bury the real ones. Pairs of satellites from the same mega-constellation, such as two Starlink satellites, are removed for a similar reason: one operator controls both and coordinates their paths. Everything else, including a Starlink satellite passing a different operator’s spacecraft, stays in.
Frequently asked questions
What is a satellite conjunction?
A predicted close approach between two objects in orbit. Most pass many kilometres apart and need no action.
Does a high probability here mean a collision is likely?
No. It is a worst-case upper bound from imprecise public data, so safe passes often show alarming numbers.
How does the ISS avoid space debris?
By firing thrusters, usually on a docked spacecraft, to shift its orbit slightly when a close approach looks risky. This happens only occasionally.
Why are the ISS’s docked spacecraft not listed?
They share its orbit and appear to approach it constantly at almost zero speed. These are not real encounters, so they are removed.
See where the station is right now, or check how space weather is affecting low Earth orbit.
Where is the ISS right now? Space weather today