After more than 40 years, NASA’s Voyager reconnects using a device last used in 1981.

At 15.4 billion miles from Earth, Voyager 1 continues its journey in interstellar space, but its time may be running out. Recently, NASA’s flight engineers feared the 47-year-old mission had reached its end when the uncrewed spacecraft unexpectedly went silent, after shutting down its primary radio transmitter used to communicate with mission control.

The issue began on October 16, when flight controllers sent a routine command to activate a heater on Voyager. However, two days later, no response came back. The team discovered that something had triggered Voyager’s fault protection system, which turned off its X-band transmitter, leading to a complete communication blackout by October 19.

With the main radio offline, hope dwindled. However, Voyager 1 has a backup transmitter that uses a different, but much fainter, frequency. The team didn’t know if it would still work, especially given the probe’s incredible distance. Days later, engineers with the Deep Space Network—a series of large radio dishes on Earth—managed to pick up a faint signal on the S-band transmitter, a device last used in 1981, according to NASA.

“The team is now working to gather information that will help them figure out what happened and return Voyager 1 to normal operations,” NASA shared in a recent update.

Both Voyager 1 and its twin, Voyager 2, have been exploring space for nearly half a century, far surpassing their original five-year lifespan. Launched in 1977 to study Jupiter and Saturn, their moons, and Saturn’s rings, the mission expanded after success to include Uranus and Neptune, making the Voyagers the only spacecraft to have explored four planets, 48 moons, and several magnetic fields and ring systems.

Voyager 1 made history in August 2012, becoming the first human-made object to reach interstellar space, a region filled with material from stars that died millions of years ago. Voyager 1 and 2 remain the only spacecraft operating beyond the heliosphere, the sun’s bubble of influence. Now the farthest human-made object from Earth, Voyager 1 travels at over 38,000 mph, with a 23-hour delay for messages to travel each way between the spacecraft and mission control.

To conserve power, flight controllers have periodically shut down systems, aiming to keep the spacecraft operational through at least 2025. It remains unclear why Voyager 1’s fault protection system disabled the main transmitter. Such onboard issues can occur if power is overdrawn, triggering the system to shut down less critical equipment. Data suggests, however, that Voyager 1 should have had enough power to operate the heater without incident.

Navigating interstellar space presents unique challenges, as no human-made technology has ventured through this high-radiation environment. Last month, the team also resolved a thruster issue, with each challenge highlighting the complexity and caution required at this stage of the mission.

“All the decisions we will have to make going forward are going to require a lot more analysis and caution than they once did,” said Voyager project manager Suzanne Dodd.