Home›Maneuver Tracker›Close Approaches›USA 81 ⟷ IRIDIUM 100
MediumProximity
United StatesUSA 81NORAD 21949 · launched Apr 1992Military payload
5.87kmPredicted miss distance
United StatesIRIDIUM 100NORAD 42956 · launched Oct 2017Payload
Final forecastFinal forecast, made minutes before the pass.
After the passBest estimate, from the orbit data published nearest its time: 5.84 km at 31 Oct 06:23 UTC.
Closest approach31 Oct 202606:23 UTC
Relative speed3.49 km/sat the closest approach
Altitude790 kmlow Earth orbit
Last confirmed31 Oct06:22 UTC · final forecast
Track USA 81Track IRIDIUM 100All approaches
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US USA 81 and US IRIDIUM 100 were predicted to reach a closest approach of 5.87 km at 2026-10-31 06:23 UTC, at a relative speed of 3.49 km/s. Final forecast, made minutes before the pass. Best estimate after the pass, from the orbit data published nearest its time: 5.84 km at 31 Oct 06:23 UTC. 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.

Why it mattersBoth objects are catalogued as payloads. Screening continues as new element sets arrive; operators act on their own conjunction data.

The Two Objects

Dossiers from the satellite directory
USA 81Payload
NORAD 21949
CountryUS
Launched1992-04-25
OrbitLEO · 782 × 785 km
COSPAR1992-023A
Maneuver capableUnknown
Profile →Globe →
IRIDIUM 100Payload
NORAD 42956
CountryUS
Launched2017-10-09
OrbitLEO · 776 × 779 km
COSPAR2017-061B
Maneuver capableUnknown
Profile →Globe →

Where This Happens

Altitude context
DEBRIS BELT 700–1000 KM2006001,0001,5002,000 kmTHIS PASS · 790 KMISS 420Starlink 550

At 790 km this pass sits inside the most congested band in low Earth orbit, home to the debris left by the 2007 ASAT test and the 2009 collision. 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

1 predicted pass under 10 km
Pair history · USA 81 ⟷ IRIDIUM 100
2026-10-31 06:235.87 km Final forecast3.49 km/s790 kmShown above

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

Every figure published for the pass shown above, newest first. Nothing is overwritten: a withdrawn forecast keeps its figure, with the newer check beside it, and the best estimate after the pass is a row of its own.
Computed · figure · predicted time · orbit data · by
3 Nov 18:45 UTC5.84 km Best estimate31 Oct 06:23 UTC31 Oct 05:07 UTCBest estimate
31 Oct 03:42 UTC5.87 km Forecast31 Oct 06:23 UTC30 Oct 23:56 UTCRe-check
30 Oct 21:09 UTC5.89 km Forecast31 Oct 06:23 UTC30 Oct 17:58 UTCRe-check
30 Oct 18:12 UTC5.91 km Forecast31 Oct 06:23 UTC30 Oct 13:33 UTCRe-check
30 Oct 09:31 UTC5.76 km Forecast31 Oct 06:23 UTC30 Oct 04:13 UTCRe-check
30 Oct 06:51 UTC6.10 km Forecast31 Oct 06:23 UTC30 Oct 00:30 UTCRe-check
30 Oct 06:31 UTC6.54 km Forecast31 Oct 06:23 UTC30 Oct 00:30 UTCScreen

These Objects Elsewhere

Other screened approaches · 7 days
1.58 km11-06 13:26 UTC
USA 81OPS 8364 (DMSP 4)
2.39 km11-03 03:09 UTC
USA 81OPS 3367 B
2.51 km11-02 17:51 UTC
USA 81NOAA 16 DEB

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 →