After 37 years without use, the thrusters of Voyager 1 successfully fired up Wednesday.

The only human-made object in interstellar space, the fastest and farthest spacecraft, NASA’s Voyager 1 has been flying for 40 years. But how can it still communicate with Earth?

The spacecraft relies on small devices called thrusters to orient itself to our planet. 13 billion miles away from Earth, thrusters fire in tiny “puffs”, or pulses lasting milliseconds, managing to rotate the spacecraft so that its antenna points at our planet.

“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, Pasadena, California.

Read also: Voyager 1 Celebrates 40 Years Of Space Travel

NASA says that since 2014 engineers have noticed that the thrusters Voyager 1 has been using to orient the spacecraft, called “attitude control thrusters,” have been degrading, requiring more puffs to give off the same amount of energy.

They’ve analyzed the options and predicted how the spacecraft would respond in different scenarios, finally agreeing on an unusual solution: Try giving the job of orientation to a set of thrusters that had been asleep for 37 years.

On Tuesday, Nov. 28, 2017, 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 traveled through space, taking 19 hours and 35 minutes to reach an antenna in Goldstone, California, that is part of NASA’s Deep Space Network. On Wednesday, Nov. 29, they learned the TCM thrusters worked perfectly — and just as well as the attitude control thrusters.- NASA.gov