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Since ISS is an evolving structure which center of mass flucuates in position depending on added or removed modules, could Canadarm or latest European robotic arm be used to manipulate attitude thrusters like it could manipulate any other thing or tool?

This way the attitude thrusters could consist of one single nozzle pointed where it should relative to center of mass and benefit from large lever arm and degrees of freedom that are allowed by the arm.

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    $\begingroup$ Would the propellant tanks be attached to the nozzle or would flexlines connect them? $\endgroup$
    – Organic Marble
    Commented Jul 25, 2021 at 20:35
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    $\begingroup$ @OrganicMarble I think tanks+nozzle is one single device, either expendable or refueled somewhere, somehow $\endgroup$
    – user19132
    Commented Jul 25, 2021 at 20:42
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    $\begingroup$ @OrganicMarble maybe refueled or left empty where they've been picked up (progress module?) thanks for adding the missing tag $\endgroup$
    – user19132
    Commented Jul 25, 2021 at 20:51
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    $\begingroup$ My first thought was this makes no sense. That was followed by my second and third thoughts that said the same. $\endgroup$
    – David Hammen
    Commented Jul 27, 2021 at 13:38

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Thrusters have many components and subsystems directly linked to this ISS: moving them would add more constraints than fixing them and modifying the angle of incidence (like you currently can with gimbals). In addition, those manoeuvers are relatively rare (a few times a year tops) and monopolizing a tool as useful as the Canadarm would be extremely limiatating for astronauts who use them during every EVA.

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  • $\begingroup$ You last sentence does not make sense. The arm would only be involved when the thruster gets relocated (if moved to new fixed mount), or during reboost which as you state are relatively rare. Surely you did not envision the arm holding the thruster in readiness at all times? $\endgroup$
    – CuteKItty_pleaseStopBArking
    Commented Jul 26, 2021 at 7:45
  • $\begingroup$ No but I would expect the installation of the thrusters to take a significant amount of time that could affect the EVAs and would higher the risks astronauts have to face during the operation, as a thruster is nothing more than a direction-controlled bomb $\endgroup$
    – elle.delle
    Commented Jul 26, 2021 at 8:08
  • $\begingroup$ yes. but they would only be needed to adjust every time the center of gravity of the ISS changes significantly, and the change is not caused by a docked capsule (which can contribute to match its own mass). So in effect, once per additional station module installation or relocation, which is not often at all $\endgroup$
    – CuteKItty_pleaseStopBArking
    Commented Jul 26, 2021 at 8:50
  • $\begingroup$ Currently, the Russian Progress' eight engines are responsible for evenly pushing the ISS to its correct attitude with its current center of gravity. Those are composed of a mix of Hydrazine and UDMH and the tanks alone weight 800 kg - empty. I highely doubt any space agency would send their astronauts to play around those - even once every 20 years. $\endgroup$
    – elle.delle
    Commented Jul 26, 2021 at 9:16
  • $\begingroup$ aha. now THAT is a valid objection to the idea. stating that a mobile thruster unit would monopolize the arm is not. $\endgroup$
    – CuteKItty_pleaseStopBArking
    Commented Jul 26, 2021 at 9:31

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