Voyager 1 is Still Not Well

Back in early December, NASA/JPL released some grim news on the status of Voyager 1, now well past the solar system in interstellar space.  As I said at the time, it seemed a lot like a stroke, or perhaps Alzheimer's disease.  While the probe seemed to take commands, it only responded with incoherent ramblings.  

The Voyagers are now in the 46th year of their four year missions and are the two probes that have gone farthest from Earth and are still in routine contact with controllers on the ground.  Light travel to Voyager 1 is over 22 and a half hours each way.  That means to send it a command that would generate a response and get that response back to Earth together take over 45 hours - just short of two full days.  That puts a premium on really understanding what you're going to transmit and knowing what the expected results could be.  

As of Feb. 6, NASA said the team remains working on bringing the spacecraft back to proper health. "Engineers are still working to resolve a data issue on Voyager 1," NASA's Jet Propulsion Laboratory said in a post on X (formerly Twitter). "We can talk to the spacecraft, and it can hear us, but it's a slow process given the spacecraft's incredible distance from Earth."

It helps to know that Voyager has three computer systems on board, together called the Flight Data System (FDS), and engineers working on the problem have concluded it's what they call the telecommunications unit (TMU). When it was developed five decades ago, Voyager's Flight Data Subsystem was an innovation in computing. It was the first computer on a spacecraft to make use of volatile memory. Each Voyager spacecraft launched with two FDS computers, but Voyager 1's backup FDS failed in 1981, according to Dodd. There's only so much capacity for backups of critical systems, they can't fly three of everything, and Vger has been working without a backup for 42 years.

As a result, no science or engineering data is being sent back to Earth.  They've been troubleshooting this  issue since early December and while they haven't fixed it, they're focused on the TMU.  

Then, in early February, Suzanne Dodd, Voyager project manager at NASA's Jet Propulsion Laboratory, told Ars Technica that the team might have pinpointed what's going on with the FDS at last. The theory is that the problem lies somewhere with the FDS' memory; there might be a computer bit that got corrupted. Unfortunately, though, because the FDS and TMU work together to relay information about the spacecraft's health, engineers are having a hard time figuring out where exactly the possible corruption may exist. The messenger is the one that needs a messenger.

Suzanne Dodd also said, "It would be the biggest miracle if we get it back. We certainly haven't given up. There are other things we can try. But this is, by far, the most serious since I’ve been project manager." 

The only signal Voyager 1's Earthbound engineers have received since November is a carrier tone, which basically tells the team the spacecraft is still alive. There's no indication of any other major problems. Changes in the carrier signal's modulation indicate Voyager 1 is receiving commands uplinked from Earth.

Artist’s illustration of one of the Voyager spacecraft. Credit: Caltech/NASA-JPL

My inner photographer insists that I point out that image is entirely artistic license. Or outright fiction, you can choose the word you'd like. At 22 light hours from the sun there won't be light out there.  There are no clouds of stars out there to give that pretty blue and purple backlighting. The sun itself would be brighter than the distant stars, but you could stare at it without harming your eyes.  In short, it would be pitch black out there and Voyager would be undetectable.  Invisible. Which doesn't make a pretty picture.

Voyager project manager Dodd makes some mention of the lurking, harshest reality of all.  At 46, Voyager is inescapably approaching end of life.  There may not be a fix for this, and if there is, another worse problem might be right behind this one.  The absolute best possible outcome is that they fix it and get another few years of data out of Voyager 1.