Launched in 1977 and now more than 15 billion miles from Earth, NASA’s Voyager 1 recently encountered an operational issue cutting off contact with mission control. Working through a puzzling shutdown of the spacecraft’s main radio transmitter, engineers at NASA’s Jet Propulsion Laboratory (JPL) reconnected with it on Oct. 24. This incident highlighted the challenges of managing a spacecraft that has operated far longer than its original mission intended and now functions on limited power reserves.

The trouble began on Oct. 16 when the Voyager team issued a command telling the spacecraft to turn on one of its heaters—a measure to shield its instruments from the extreme cold of interstellar space. Equipped with a fault protection system to stop breakdowns, Voyager answered strangely. Designed to automatically save power in case of an energy drain, the fault protection system turned off the main X-band transmitter, a frequency Voyager has used for decades of communication with Earth.

“The flight team correctly hypothesized that the fault protection system had lowered the rate at which the transmitter was sending back data,” NASA said in a statement. “This mode requires less power from the spacecraft, but it also changes the X-band signal that the Deep Space Network (DSN) needs to listen for.”

The system turned communication over to a backup transmitter, the S-band, which runs at a far lower power level. The transmitter hadn’t been used since 1981 when Olivia Newton-John’s “Physical” topped the charts and Ronald Reagan moved into the White House.

The drawback, however, was this transmitting modification reduced the signal strength and complicated DSN antennas’ ability to detect Voyager’s fainter S-band transmission from such a great distance.

Redundancy saves the day yet again

The JPL engineers first thought the main signal loss from Voyager indicated a problem with the spacecraft’s fault protection system. They examined the arriving data closely in search of any trace of the faint signal of the backup transmitter. Oct. 22 saw them at last detect the S-band signal. Engineers had confirmed Voyager’s state by Oct. 24 and could restore consistent communication. They intend to keep using the backup transmitter while looking at the fault protection system to prevent needless triggering.

“Rather than risk turning the X-band back on before determining what triggered the fault protection system, the team sent a command on Oct. 22 to confirm the S-band transmitter is working,” NASA stated. “The team is now working to gather information that will help them figure out what happened and return Voyager 1 to normal operations.”

Beginning its voyage into interstellar space in 1977, Voyager 1 is still the most far-off human-made object, constantly offering data on cosmic rays, magnetic fields, and particles in a region far beyond the reach of our Sun. This special posture also makes controlling the spacecraft especially difficult. Every command and response exchange takes almost two days—almost 23 hours for a signal to travel each way—making troubleshooting a slow and careful process. Engineers must carefully select which instruments and heaters to keep running to guarantee the spacecraft’s surviving power supplies last as long as possible since Voyager 1’s systems are well beyond their expected lifetime.

This latest event emphasizes the balancing act needed to run both Voyagers. Even small duties like turning on a heater are scheduled with an eye toward long-term spacecraft health preservation. Voyagers 1 and 2 have been flying for over 47 years and are the only two spacecraft operating in interstellar space. This certainly hasn’t been the craft’s first hiccup. Their increasing age has meant a rise in the frequency and complexity of technical issues and new challenges for the mission engineering team.