how critical is passive stability?

Ah, yes, you speak of the shifting of weights inside
the cylinder. That's a completely different horse.
Dynamic rebalancing has been considered using H2O
pumped around, perhaps using electrophoresis pumps to
quickly adjust the balance of this large body.
However, I expect that significantly altering the
balance of such a massive rotating object would be
almost as hard as affecting the earths wobble by
having all the humans on earth jump up and down at
once.

We are discussing a multi mega ton gyroscope, eh? How
could the actions of a flea walking around inside it
cause it to wobble? Of course, moving large masses
around might require some planning, but isn't that
what we're good at?

Gary 7