There's a lot of miscellaneous things that can break on a spacecraft Reaction wheels (which use momentum to help you point the vehicle) are a semi common faili

There's a lot of miscellaneous things that can break on a spacecraft Reaction wheels (which use momentum to help you point the vehicle) are a semi common failire. There's usually some redundancy built in, but if enough of them wear out you'll lose stability and pointing accuracy. Even radiation-hardened electronics will wear out over time. If you look at unprocessed images from the Hubble, there's a shitload of pixels that have been fried in the cameras (the effect kind of look like stuck pixels in a computer monitor)