The Voyager 1 spacecraft has been flying for over 40 years now, an incredible history. But recently, mission controllers at JPL have found that the attitude control thrusters appear to have degraded performance. Concerned they might not last out the last few years of expected performance, JPL decided to try something else — to use the trajectory correction maneuver thrusters. These thrusters were responsible for changes to the spacecraft’s actual trajectory, and are larger than the attitude control thrusters. More importantly, they have a lot fewer hours of operation. But there was a catch — the last time these thrusters fired, it was to set up the flyby of Saturn in 1980. Could they still find the documentation to write a program to fire the thrusters in tiny pulses for attitude control? And would the thrusters still work after being asleep for so long?
Well, the answer to both was “yes”, and JPL believes they’ve bought at least another 2-3 years for the spacecraft. With the expected end of mission (or, end of extended-extended-extended-n-times-extended-mission) in 2020 or so, that’s pretty significant; this means they are back to expecting that declining electrical power output will be what kills the spacecraft.
At any rate, these magnificently engineered engines are working like a champ, and they will continue to be used, possibly for the remainder of the mission, with the attitude control thrusters now relegated to a backup role. Meanwhile, they are exploring the same option for Voyager 2, although its attitude control thrusters still appear healthy.