Considering how the odds are stacked against him, the new life opportunity of Voyager 1, even if it's only three years at most, is nothing short of a miracle. The spacecraft has been traveling through space for 40 years and, since 2012, it has left our solar system, becoming the first and so far only interstellar object created by man. Then, when crucial parts begin to fail, there is almost no hope. Fortunately, Voyager 1 seems to refuse to give up the ghost and its reserve propellers have been fired successfully, even after being unused for 37 years.
Voyager 1 does not really need propellers to continue navigating through space. However, he needs them to orient himself in order to communicate with the Earth. These "attitude control drivers", as they are called, have been degraded for three years, spending a greater amount of energy and shortening the lifespan of the Voyager 1 mission.
Fortunately, those are not the only drivers to board. Voyager 1 also has "trajectory correction maneuver" or TCM thrusters, but they worked differently and were used for a different purpose, despite having the same construction. The main propellers fired pulses called "puffs" to subtly rotate the spacecraft. The TCM, on the other hand, shot continuously when in use.
TCMs have not been used since 1980, however, when they were needed to stabilize Voyager 1 during their flight of Jupiter, Saturn and their moons. NASA scientists and propulsion experts were also not sure if the thrusters would work in short bursts, if they worked. Having slept for almost four decades, the odds seemed low.
Then you can imagine their mixture of disbelief and joy when, on November 29, they received data that the Voyager 1 backup thrusters ran smoothly in a test. Of course, each of the four propellers would need to be heated individually, which would consume even more energy than it would normally do. The alternative, however, would be to give Voyager 1 an early retirement. NASA plans to switch to backup engines in January and when there is no longer enough energy for them, return to the main ones. They also plan to perform a similar test on the youngest Voyager 2, in the event that their main thrusters still work perfectly.