The problem with Voyager 1 was first detected in November. At the time, NASA said it was still in contact with the spacecraft and could see that it was receiving signals from Earth. But what was being relayed back to mission controllers — including science data and information about the health of the probe and its various systems — was garbled and unreadable.
That kicked off a monthslong push to identify what had gone wrong and try to save the Voyager 1 mission.
Spilker said she and her colleagues stayed hopeful and optimistic, but the team faced enormous challenges. For one, engineers were trying to troubleshoot a spacecraft traveling in interstellar space, more than 15 billion miles away — the ultimate long-distance call.
“With Voyager 1, it takes 22 1/2 hours to get the signal up and 22 1/2 hours to get the signal back, so we’d get the commands ready, send them up, and then like two days later, you’d get the answer if it had worked or not,” Spilker said.
The team eventually determined that the issue stemmed from one of the spacecraft’s three onboard computers. Spilker said a hardware failure, perhaps as a result of age or because it was hit by radiation, likely messed up a small section of code in the memory of the computer. The glitch meant Voyager 1 was unable to send coherent updates about its health and science observations.
NASA engineers determined that they would not be able to repair the chip where the mangled software is stored. And the bad code was also too large for Voyager 1’s computer to store both it and any newly uploaded instructions. Because the technology aboard Voyager 1 dates back to the 1960s and 1970s, the computer’s memory pales in comparison to any modern smartphone. Spilker said it’s roughly equivalent to the amount of memory in an electronic car key.
The team found a workaround, however: They could divide up the code into smaller parts and store them in different areas of the computer’s memory. Then, they could reprogram the section that needed fixing while ensuring that the entire system still worked cohesively.
That was a feat, because the longevity of the Voyager mission means there are no working test beds or simulators here on Earth to test the new bits of code before they are sent to the spacecraft.
“There were three different people looking through line by line of the patch of the code we were going to send up, looking for anything that they had missed,” Spilker said. “And so it was sort of an eyes-only check of the software that we sent up.”
The hard work paid off.
NASA reported the happy development Monday, writing in a post on X: “Sounding a little more like yourself, #Voyager1.” The spacecraft’s own social media account responded, saying, “Hi, it’s me.”
So far, the team has determined that Voyager 1 is healthy and operating normally. Spilker said the probe’s scientific instruments are on and appear to be working, but it will take some time for Voyager 1 to resume sending back science data.
Voyager 1 and its twin, the Voyager 2 probe, each launched in 1977 on missions to study the outer solar system. As it sped through the cosmos, Voyager 1 flew by Jupiter and Saturn, studying the planets’ moons up close and snapping images along the way.
Voyager 2, which is 12.6 billion miles away, had close encounters with Jupiter, Saturn, Uranus and Neptune and continues to operate as normal.
In 2012, Voyager 1 ventured beyond the solar system, becoming the first human-made object to enter interstellar space, or the space between stars. Voyager 2 followed suit in 2018.
Spilker, who first began working on the Voyager missions when she graduated college in 1977, said the missions could last into the 2030s. Eventually, though, the probes will run out of power or their components will simply be too old to continue operating.
Spilker said it will be tough to finally close out the missions someday, but Voyager 1 and 2 will live on as “our silent ambassadors.”
Both probes carry time capsules with them — messages on gold-plated copper disks that are collectively known as The Golden Record. The disks contain images and sounds that represent life on Earth and humanity’s culture, including snippets of music, animal sounds, laughter and recorded greetings in different languages. The idea is for the probes to carry the messages until they are possibly found by spacefarers in the distant future.
“Maybe in 40,000 years or so, they will be getting relatively close to another star,” Spilker said, “and they could be found at that point.”