For the first time since 1980, the most distant spacecraft humanity has ever launched has fired its backup thrusters.
Voyager 1 is the only man-made object in interstellar space, having travelled 21 billion kilometres in 40 years.
Its main thrusters have been degrading over the last few years, and without a NASA garage handy for repairs, scientists at NASA's Jet Propulsion Laboratory (JPL) in California had to resort to the spares - which haven't been touched since before the first space shuttle launched.
"The Voyager flight team dug up decades-old data and examined the software that was coded in an outdated assembler language, to make sure we could safely test the thrusters," said Chris Jones, chief engineer at JPL.
They were last used on November 8, 1980, as Voyager 1 flew by Saturn.
"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.
Signals between Earth and Voyager take more than 19 hours to arrive.
Around 2025, Voyager's radioactive power source will expire and all contact will be lost. If its journey is uninterrupted, it'll pass through the Oort cloud in 300 years, and fly by star Gliese 445 in 40,000 years.