At a time when technology is updated on the fly, the reliance on decades’ old systems for space research has come as both a surprise and cause for excitement. Following recent communication issues, Nasa’s Voyager 1 spacecraft resorted to using a backup radio transmitter that has been inactive for 43 years. When Voyager 1 and Voyager 2 were launched in 1977, they were only expected to operate for five years and check out shortly after their visits to Jupiter, Saturn, Uranus, and Neptune. Instead, their lifespans have extended ten-fold despite flying through the deadly radiation belts of Jupiter and decades of being exposed to cosmic rays and intense cold as they hurtled out of the solar system. The Voyager duo are the only spacecraft to ever fly in interstellar space (the space between stars).
Over the years, Mission Control has nursed the Voyagers along in order to extend their service life. Unused systems are shut down and shut down ones are brought back to replace failing ones. There’s also a lot of delicate energy budgeting as the engineers keep a close eye on the nuclear power systems as they inevitably use up their plutonium fuel. When the flight team, based at Nasa’s Jet Propulsion Laboratory in Southern California, beams instructions to the spacecraft from Nasa’s Deep Space Network (DSN), a global array of giant radio antennas, Voyager 1 sends back engineering data that the team assesses to determine how the spacecraft responded to the command. This process normally takes a couple of days — almost 23 hours for the command to travel more than 24bn km from Earth to the spacecraft, and another 23 hours for the data to travel back.
On October 16, the flight team sent a command to turn on one of the spacecraft’s heaters. While Voyager 1 should have had ample power to operate the heater, the command triggered the fault protection system. The team learned of the issue when the DSN couldn’t detect Voyager 1’s signal on October 18. The spacecraft typically communicates with Earth using an X-band radio transmitter, named for the specific frequency it uses. The flight team correctly hypothesised that the fault protection system had lowered the rate at which the transmitter was sending back data. This mode requires less power from the spacecraft, but it also changes the X-band signal that the DSN needs to listen for. Engineers found the signal later that day, and Voyager 1 otherwise seemed to be in a stable state as the team began to investigate what had happened.
Then, on October 19, communication appeared to stop entirely. The flight team suspected that Voyager 1’s fault protection system was triggered twice more and that it turned off the X-band transmitter and switched to a second radio transmitter called the S-band. While the S-band uses less power, Voyager 1 had not used it to communicate with Earth since 1981. It uses a different frequency than the X-band transmitters signal is significantly fainter. The flight team was not certain the S-band could be detected at Earth due to the spacecraft’s distance, but engineers with the DSN were able to find it.
Rather than risk turning the X-band back on before determining what triggered the fault protection system, the team sent a command on October 22 to confirm the S-band transmitter is working. On October 24, Nasa reconnected with Voyager 1 after a brief pause in communications. Voyager 1 and its twin Voyager 2 are the only spacecraft ever to operate outside the heliosphere, the protective bubble of particles and magnetic fields generated by the Sun. Voyager 1 reached the interstellar boundary in 2012, while Voyager 2 (travelling slower and in a different direction than its twin) reached it in 2018. While spacecraft’s advanced age and distance from Earth can make maintenance challenging, Voyager 1 continues to return vital data from beyond the solar system.