For five months, experts worked tirelessly to troubleshoot and restore communication with Voyager 1, a spacecraft nearly half a century into its journey.
After five months of working to reestablish contact with the farthest human-made object, the Voyager 1 spacecraft, NASA announced on April 20 that the spacecraft had finally "phoned home." For the engineers and scientists working on NASA's longest-operating space mission, it was an exhilarating moment of relief.
"A Collective Sigh of Relief"
"We all came in that Saturday morning and hung out and had doughnuts, waiting for the data to come down from Voyager. We knew exactly when it was going to come through, and it was just a very quiet, almost reverent feeling in the room as we watched the data come in," said Linda Spilker, Voyager 1 project scientist at NASA's Jet Propulsion Laboratory (JPL).
When the spacecraft finally responded, the room erupted in cheers. "There was lots of hooping and high-fiving, just a collective sigh of relief. After all of the hard work that had gone into troubleshooting Voyager and getting the signal back, it was a big relief and a really good feeling," Spilker said.
The Malfunction
Voyager 1's issue was first detected in late November. At the time, NASA was still able to communicate with the spacecraft and could see that it was receiving signals from Earth. But what was being sent back to ground control - including science data, health and status information about the spacecraft and its systems - was garbled and unreadable.
This began a months-long effort to determine what had gone wrong and save Voyager 1. Spilker and her colleagues remained hopeful and optimistic, but they faced formidable challenges. For one, engineers were attempting to fix the issue while the spacecraft was traveling in interstellar space, over 15 billion miles from Earth.
A "Giant" Distance
"With Voyager 1, it takes about 22 and a half hours to send a signal, and another 22 and a half hours to get a signal back. So we would prepare commands, send them up, and then about two days later, we would get a response as to whether they worked or not," Spilker said.
Eventually, the team of experts deduced that the issue originated in one of the spacecraft's three computers. Spilker said a hardware glitch - possibly related to age or radiation - likely corrupted a section of code in the computer's memory. This corruption prevented Voyager 1 from properly transmitting information related to its health and its scientific observations.
A Creative Solution
The NASA engineers determined that they could not fix the corrupted memory chip. The corrupted code was also too large for Voyager 1's computer to store both it and any new instructions sent from Earth. Since Voyager 1's technology is from the 1960s and 1970s, its computer memory is far less powerful than today's smartphones. Spilker said it's roughly equivalent to the amount of storage present in a modern car key fob.
The team eventually came up with a workaround. They broke the code down into smaller pieces and stored them in different locations in the computer's memory. They then reprogrammed the necessary part while keeping the entire system running seamlessly. This was no small feat, as Voyager 1 was built well before there were testing platforms or simulations on Earth to check new code before it was sent up to the spacecraft.
"We had three people independently look at every line of the code that we were going to upload, just to make sure that we weren't missing anything, like a visual inspection," Spilker said. Their painstaking work ultimately paid off, and communication with Voyager 1 was restored.
Voyager 1 Still Going Strong
To date, the team has determined that Voyager 1 is in overall good health and operating nominally, NBC News reported on April 27. Spilker said the spacecraft's science instruments are still on and appear to be functioning, though it will take some time for the spacecraft to begin transmitting scientific data again.
Voyagers' Legacy
Voyager 1 and its twin, Voyager 2, were launched into space in 1977 with the mission of exploring the outer planets of our solar system. According to Spilker, the spacecraft could last into the 2030s. Eventually, they will either run out of power or their components will become too old to function.
While the day will be bittersweet when Voyager 1 and 2 finally cease operation, they will continue to exist as "silent ambassadors." Both spacecraft carry valuable messages on their Golden Records. The records contain images and sounds that represent life on Earth and human culture, including music, animal noises, laughter, and greetings recorded in multiple languages. The spacecraft will carry these messages until they are perhaps discovered by future space explorers.
"They will come relatively close to another star in about 40,000 years, and that's when they will be most likely to be found," Spilker said.