Voyager 2's close encounter with Uranus wasn't in the plan

"It was a fantastic encounter because it almost didn't happen. After Saturn, we had the scan platform problem. If that problem had not been resolved, there wouldn't have been a Uranus encounter."

""It was a testing encounter," recalled Hunt. "In the interim period between the '82 encounter with Saturn and getting to Uranus, the engineers had to reorganize how the scan platform was operating. The computer system had to be altered again. All the sequencing had to be dealt with in a new manner, and we had to prepare a wobbling spacecraft to take low-exposure images in a very dark environment and get that information back to Earth.""

Voyager 2's Uranus flyby occurred because engineers provisioned extra fuel capacity and Voyager 1's Titan encounter allowed continuation of the Grand Tour. A lubrication failure after Saturn caused the scan platform to seize on the horizontal axis, threatening major data loss and the Uranus encounter. Engineers diagnosed and remotely corrected the lubrication issue and reworked sequencing and computer operations. Teams adapted to a wobbling platform, configured low-exposure imaging for the very dark environment at Uranus, and ensured science data could be returned to Earth, producing the valuable Uranus dataset.

Read at Theregister