Thread by @ProfHughLewis

Welcome to my (delayed) monthly analysis of @CelesTrak #SOCRATES conjunctions. Since 1 March 2019, SOCRATES has predicted about 9 million unique conjunctions within 5 km involving active or derelict payloads. This is a thread focused on those involving #OneWeb & #Starlink [1/n]

#OneWeb payloads have accounted for ~500,000 unique conjunction predictions since 1 March 2019 (5.5% of all predictions made), while #Starlink payloads have accounted for ~1.1 million (12.5%) [2/n]

On 1 March 2019 #SOCRATES predicted ~3860 unique conjunctions within 5 km. On 30 June 2022 the corresponding number was ~10,160, an increase of ~160%. #Starlink accounted for ~2570 (25%) & #OneWeb accounted for ~1250 (12%) [3/n]

The #SOCRATES predictions for conjunctions within 1 km paint a similar picture. In the middle of March 2022, SOCRATES predicted more than 450 unique conjunctions per day & we see close to that in the most recent predictions. The two constellations account for ~200 of those [4/n]

Just over 60% of the conjunctions NOT involving the two constellations were payload (active or derelict) on debris. About 30% were payload on payload and the remaining conjunctions were payload on rocket body [5/n]

For conjunctions predicted to involve #Starlink the pattern is generally similar [6/n]

However, for conjunctions predicted to involve #OneWeb the pattern is quite different, with a much larger proportion of conjunctions involving another payload & relatively few involving another OneWeb payload or a rocket body [7/n]

This chart shows only predicted conjunctions where the collision probability is greater than 1-in-100,000 (1E-5). This is an important threshold for #Starlink as it is the probability level that triggers a manoeuvre [8/n]

An important caveat here: the accuracy of the TLE data ingested by #SOCRATES is not sufficient for reliable estimation of the collision probability. However, the simple count of these events involving #Starlink has provided an indication of the number of manoeuvres [9/n]

The number of manoeuvres reported by #SpaceX (and shown in the chart above) can be found in the semi-annual reports submitted to the #FCC by the company [10/n]

Looking only at the conjunctions predicted by #SOCRATES for the 7 days from 30 June 2022, we can understand the altitudes where they are most frequent. The large numbers of #Starlink satellites near 550 km tend to dominate (recall that most are manoeuvrable) [11/n]

Here's the same data plotted using a logarithmic y-axis. This enables lower conjunction rates to be seen more clearly (but distorts the higher rates) [12/n]

Here's another perspective showing how the two constellations tend to dominate the predicted conjunction rates at, or near, their operational altitudes but also showing contributions at altitudes used for orbit raising & disposal [13/n]

That's all for now. My usual thanks to @TSKelso for the #SOCRATES data and ongoing support, and to @planet4589 for #Starlink and #OneWeb statistics [14/14; fin]