[dylan604]

The impact on Jupiter bit seems strange to me. Unless it's something that just pops up out of nowhere, it seems like we'd have been tracking the impactor for some time to be able to have plenty of lead time for Hubble to use its walker to slowly get into position.

[SiempreViernes]

Impactors are indeed not seen that far ahead in comparison to the Hubble time allocation time scale, so for scheduling purposes they do more or less pop up out of nowhere.

Since its not very likely that you happen to have a scheduled science target lying close to Jupiter around the time of impact, you would have to do a long slew which now takes such a long time you likely have to cancel some other science. But I think this is a general issue that will discard most targets of opportunity that Hubble could otherwise have observed.