[SaberTail]

No, the comment you're replying to is confused. These gyroscopes are entirely used for determining Hubble's orientation. Reaction wheels effect the actual rotation, and Hubble's are fine.

I think the confusion is a result of imprecise language talking about how they are used to slew the telescope. They are "used" but as feedback, in conjunction with other systems. Also, there have some prominent reaction wheels failures on other missions, and that contributes to the confusion.

[Rebelgecko]

FWIW I think 2 of the Hubble's 4 reaction wheels are dead, which also requires some interesting workarounds

[cubefox]

Thanks, this makes sense. I guess I should look up the difference between gyroscopes and reaction wheels next.

[ijustlovemath]

Per your name: https://m.youtube.com/watch?v=n_6p-1J551Y&pp=ygUG