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According to the Soyuz MS-17 Wikipedia page, the spacecraft is planned to relocate from Rassvet nadir to Poisk zenith on 10 March 2021. This 3 weeks before the next Soyuz, MS-18 arrives.

From Wikipedia, Soyuz MS-18 is planned to dock Rassvet nadir, and will stay there for the duration of its stay.

Why won't Soyuz MS-17 dock to Poisk zenith from the start?
Or why can't Soyuz MS-18 dock to Poisk zenith, without relocating MS-17?

Note that this redocking and the Soyuz handover will happen with SpaceX Dragon Crew-2 docked on the US segment.

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    $\begingroup$ Some of it is to keep the ports occupied, and control exposure to empty space. They prefer to keep them all occupied. Pirs is being discarded sometime soon, if Nauka ever launches. $\endgroup$
    – geoffc
    Sep 30 '20 at 17:29
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    $\begingroup$ It appears that Poisk has an issue with the Kurs system installed on it, but I don't have time to confirm ATM. space.com/… $\endgroup$ Sep 30 '20 at 17:37
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I have not found a reason explicitly stated so some deductive reasoning was used

When the unpiloted Soyuz MS-14 tried to dock to Poisk in August 2019 it failed with an automated abort. Analysis pointed to "a faulty amplifier in the Poisk module’s passive KURS system".

To get MS-14 docked, the crew of Soyuz MS-13 boarded it, undocked it from the Service Module, and docked it manually to Poisk, avoiding the use of the faulty Kurs system. MS-14 then docked to the Service Module using its functional Kurs.

Given that history, and the fact that a goal of the MS-18 mission is to replace the Poisk Kurs system, I feel justified in deducing that the goal of this relocation is to prevent using the Poisk Kurs system.

References

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  • $\begingroup$ Relocations happen somewhat often though (I mean relatively). This would only apply to post ms-14 ones. Did every relocation have reasons unrelated to the other relocations? $\endgroup$ Nov 15 '20 at 11:43

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