Engineers say the thrusters have been degrading
NASA says its farthest and fastest spacecraft has fired up its engines after 37 years without use.
The Voyager 1 spacecraft is the only human-made object in interstellar space.
The spacecraft, which has been flying for 40 years, relies on small thruster devices to move itself so it can communicate with Earth.
These thrusters fire in tiny pulses, or "puffs," lasting milliseconds, to subtly rotate the spacecraft so that its antenna points at the planet.
NASA says the Voyager team is now able to use a set of four backup thrusters which have been dormant since 1980.
Suzanne Dodd, project manager for Voyager at NASA's Jet Propulsion Laboratory, said: "With these thrusters that are still functional after 37 years without use, we will be able to extend the life of the Voyager 1 spacecraft by two to three years."
Since 2014, engineers have noticed that the thrusters Voyager 1 has been using have been degrading.
Over time, the thrusters require more puffs to give off the same amount of energy. At 13 billion miles from Earth, there's no mechanic nearby to get a tune-up.
The Voyager team then assembled a group of propulsion experts to study the problem.
Chris Jones, Robert Shotwell, Carl Guernsey and Todd Barber analysed options and predicted how the spacecraft would respond in different scenarios.
They agreed on an unusual solution: Try giving the job of orientation to a set of thrusters that had been asleep for 37 years.
"The Voyager flight team dug up decades-old data and examined the software that was coded in an outdated assembler language, to make sure we could safely test the thrusters," Chris Jones said.
In the early days of the mission, Voyager 1 flew by Jupiter, Saturn, and important moons of each.
On Tuesday November 28th, Voyager engineers fired up the four thrusters for the first time in 37 years and tested their ability to orient the spacecraft using 10-millisecond pulses.
The following day, they learned the thrusters worked perfectly.
"The Voyager team got more excited each time with each milestone in the thruster test. The mood was one of relief, joy and incredulity after witnessing these well-rested thrusters pick up the baton as if no time had passed at all," propulsion engineer Todd Barber said.
The plan going forward is to switch to the thrusters in January.
To make the change, Voyager has to turn on one heater per thruster, which requires power - a limited resource for the aging mission.
When there is no longer enough power to operate the heaters, the team will switch back to the attitude control thrusters.
Voyager 1 and 2 achieve 40 years of operation and exploration this August and September.
Voyager 1 is in interstellar space and Voyager 2 is currently in the 'Heliosheath' - the outermost layer of the heliosphere where the solar wind is slowed by the pressure of interstellar gas.
Watch Voyagers' epic journey through the solar system below: