In article ,
says...

Could this be a mass issue of some kind, ie it has to be balanced to keep
any twisting or other unfortunate problems from occuring when its moved for
avoidiing action or reboosting?

I'm sure that's part of it along with available power, drag, and etc.
Plus this is NASA. Backups for everything likely means they've already
"allocated" the other CBM ports for other purposes. Plus, as Brian
mentioned, some CBM ports are physically blocked from use by other parts
of the station even though they don't have anything attached.

Jeff
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