NASA has fired up the thrusters aboard the Voyager 1 spacecraft - the only human-made object in interstellar space - for the first time in 37 years.
The spacecraft which has been flying for 40 years, relies on small devices called thrusters to orient itself so it can communicate with Earth.
These thrusters fire in tiny pulses, or "puffs," lasting mere milliseconds, to subtly rotate the spacecraft so that its antenna points at our planet.
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"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," said Suzanne Dodd, project manager for Voyager at NASA's Jet Propulsion Laboratory (JPL) in the US.
Since 2014, engineers have noticed that the thrusters Voyager 1 has been using to orient the spacecraft, called "attitude control thrusters," 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 shop nearby to get a tune-up.
Scientists 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"The Voyager flight team dug up decades-old data and examined the software that was coded in an outdated assembler language, to make sure we could safely test the thrusters," said Jones, chief engineer at JPL.
In the early days of the mission, Voyager 1 flew by Jupiter, Saturn, and important moons of each. To accurately fly by and point the spacecraft's instruments at a smorgasbord of targets, engineers used trajectory correction manoeuvre (TCM) thrusters that are identical in size and functionality to the attitude control thrusters, and are located on the back side of the spacecraft.
However, since Voyager 1's last planetary encounter was Saturn, the Voyager team had not needed to use the TCM thrusters since November 8, 1980.
Back then, the TCM thrusters were used in a more continuous firing mode; they had never been used in the brief bursts necessary to orient the spacecraft.
On November 28, Voyager engineers fired up the four TCM thrusters for the first time in 37 years and tested their ability to orient the spacecraft using 10-millisecond pulses.
The team waited eagerly as the test results travelled through space, taking 19 hours and 35 minutes to reach an antenna in the US that is part of NASA's Deep Space Network.
On November 29, they learned the TCM thrusters worked perfectly and just as well as the attitude control thrusters.
The plan going forward is to switch to the TCM thrusters in January.
To make the change, Voyager has to turn on one heater per thruster, which requires power - a limited resource for the ageing mission.
When there is no longer enough power to operate the heaters, the team will switch back to the attitude control thrusters.
