Various news outlets reported on the Chinese government complaining about SpaceX Starlink satellites (#1095 and #2305) getting so close to their Tiangong Space Station that they had to initiate evasive maneuvers to avoid a collision. The Chinese government requested the United Nations draw attention to this incident in the context of the responsibilities of states parties to the Outer Space Treaty.

The incidents are described as follows:

1. The first collision avoidance
As from 19 April 2020, the Starlink-1095 satellite had been travelling stably in orbit at an average altitude of around 555 km. Between 16 May and 24 June 2021, the Starlink-1095 satellite manoeuvred continuously to an orbit of around 382 km, and then stayed in that orbit. A close encounter occurred between the Starlink-1095 satellite and the China Space Station on 1 July 2021. For safety reasons, the China Space Station took the initiative to conduct an evasive manoeuvre in the evening of that day to avoid a potential collision between the two spacecraft.

2. The second collision avoidance
On 21 October 2021, the Starlink-2305 satellite had a subsequent close encounter with the China Space Station. As the satellite was continuously manoeuvring, the manoeuvre strategy was unknown and orbital errors were hard to be assessed, there was thus a collision risk between the Starlink-2305 satellite and the China Space Station. To ensure the safety and lives of in-orbit astronauts, the China Space Station performed an evasive manoeuvre again on the same day to avoid a potential collision between the two spacecraft.

The full text can be found here.

Question: how close did Starlink-1905 and Starlink-2305 get to the Tiangong space station?

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    $\begingroup$ Your summary of the complaint "getting so close to their Tiangong Space Station" misses an important point in the complaint that both satellites were said to be continuously maneuvering and so collision prediction was difficult. "As the satellite was continuously manoeuvring, the manoeuvre strategy was unknown and orbital errors were hard to be assessed..." Certainly "how close did they get" is a valid question that can be answered (within several km errors) from TLEs, but the complaint was in large part about the unpredictable maneuvering which led them to give the Starlinks a wide berth. $\endgroup$
    – uhoh
    Dec 31, 2021 at 17:50
  • $\begingroup$ @uhoh Your quote is from the 2305 encounter; for 1095 there is no mention of tracking difficulties. As I understand it, 1095 just moved from one orbit to another without notification, coming close to the CSS. In any case, in both situations the separation was considered (by China) to be dangerously small, and I am curious to know how small, even if the error bars were big. $\endgroup$
    – Ludo
    Jan 1, 2022 at 12:29
  • $\begingroup$ @I didn't mention tracking difficulties but yes for 1095 closeness alone after the maneuvering stopped is the complain. $\endgroup$
    – uhoh
    Jan 1, 2022 at 16:24

1 Answer 1


Jonathan McDowell, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics, did calculations regarding how close the Chinese Space Station came to S-2305, and it's quite close.

A reply in that thread shows that the approach was as close as 3-4 km. However, that was after the avoidance maneuver, so it's unclear how close they would have come without maneuvers.

Separation distance vs time for CSS/S2305 close pass, chart by Jonathan McDowell

He provided also the following plots for apogee/perigee of both space vehicles, for the S-1095 encounter and the S-2305 encounter. It appears that S-1095 did some maneuvering also.

S-1095/CSS encounter, plot by Jonathan McDowell

S-2305/CSS encounter, plot by Jonathan McDowell


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