The 47-year-old Voyager 1 spacecraft is back in touch with NASA after a technical problem caused a multi-day blackout with the historic mission, which is billions of miles away in interstellar space.

Voyager 1 is now using a radio transmitter it hasn’t used since 1981 to stay in touch with its team on Earth. Meanwhile the engineers are working to figure out what went wrong and lost contact with the aging spacecraft.

The spacecraft was launched in September 1977 and despite its age, the team slowly turned off components to save energy, allowing Voyager 1 to send back unique science data from 24 billion kilometers away.

It is the farthest spacecraft from Earth, operating beyond the heliosphere, and its instruments directly sample interstellar space.

The new problem is one of several the aging vehicle has faced in recent months, but the Voyager team continues to find creative solutions so the famed explorer can zoom along on its cosmic journey into uncharted territory.

Occasionally, engineers send commands to Voyager 1 to turn on some of its heaters and hot components that have been damaged by radiation over the decades, said Bruce Waggoner, Voyager’s mission assurance manager. Heat can help reverse radiation damage, which degrades the performance of spacecraft components, he said.

The messages are transmitted to Voyager from mission control at NASA’s Jet Propulsion Laboratory in Pasadena, California, via the agency’s Deep Space Network. The radio antenna system on Earth helps the lab communicate with Voyager 1 and Voyager 2, as well as other spacecraft exploring our solar system.

Voyager 1 then sends back the data to show how it responds to the commands. It takes about 23 hours for a message to travel one way.

But when a command was sent to the heater on October 16, something triggered the spacecraft’s autonomous fail-safe system. If the spacecraft draws more power than it should, the fault protection system automatically disables systems that are not necessary to save power.

What caused the technical problem

The team discovered the problem when it was unable to detect the spacecraft’s response signal over the Deep Space Network on October 18.

The Voyager 1 has been using one of its two radio transmitters, called X-band after the frequency it uses, for decades. Meanwhile, the other transmitter, called S-band, which uses a different frequency, has not been used since 1981 because its signal is much weaker than that of X-band.

Engineers suspect that the anti-error system slowed the rate at which data was sent back from the transmitter, which changed the nature of the signal being shared from Voyager 1 to the Deep Space Network monitors. The Voyager 1 team finally detected the probe’s response later on October 18 by examining signals received by the Deep Space Network.

But on October 19, communication with Voyager 1 appeared to have completely ceased.

The team believes the fault protection system activated twice more, which may have disabled the X-band transmitter and switched the spacecraft to the less-powerful S-band transmitter, NASA said.

While the Voyager 1 team wasn’t sure the faint S-band signal would be detectable due to the spacecraft’s distance from Earth, Deep Space Network engineers detected it.

The team will not send Voyager 1 commands to reactivate the X-band transmitter until they determine what triggered the fault protection system, which could take weeks. Engineers are cautious because they want to determine if there are any potential hazards from X-band activation.

If the team can get the X-band transmitter working again, the device may be able to relay data that could reveal what happened, Wagoner said.

Meanwhile, engineers sent a message to Voyager 1 on October 22nd to check that the S-band transmitter was working, and received confirmation on October 24th. But it’s not a solution the team wants to rely on for long.

“The S-band signal is too weak to be used long-term,” Wagoner said. “So far, the team has not been able to use it to get telemetry (information about the health and status of the spacecraft), let alone science data. But it allows us to at least send commands and make sure the spacecraft is still pointed toward Earth.”

This transmitter switch is just one of many innovative things NASA has used to overcome its communication challenges.