The Hubble Space Telescope was not working for a short, but very disturbing period in this year. It wasn't clear if it would ever start again. There was something wrong with the electronics, and switching to the backup didn't work properly. It was an emotional time for me, as well as many others in the astronomy community.
The death of an orbiting instrument is one my worst nightmares. The scene in Gravity where Hubble is destroyed by high-speed space debris made me weep. It will always be classified as