46 Years Later, This Iconic Pair Of NASA Spacecraft Are Still Sending Signals Home

Besides 46 years of science, the aging twin spacecraft have taught engineers how to improvise -- and the value of redundancy.

1981:  A simulation of the space probe Voyager 2 preparing to leave our solar system to become the f...
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Voyager 1 might be getting better after its recent bout of aphasia.

Since November, NASA’s Voyager 1 spacecraft has been speaking in electronic gibberish. NASA still hasn’t pinpointed the cause of the problem, but a likely culprit is a cosmic ray that corrupted a single bit of data in part of the spacecraft’s Flight Data System; specifically, the part that converts information about the spacecraft's status and data into binary code to send back to Earth. Instead of coherent lines of code, Voyager has been sending home random strings of 0s and 1s that don’t mean anything.

But over the last couple of weeks, Voyager 1’s issues seem to be improving. It’s putting its 0s and 1s together in patterns, not just random sequences. However, these patterns are more like baby babble than language.

“They're not exactly what we would expect, but they do look like something that can show us that the FDS is at least partially working.” Voyager program manager Suzanne Dodd tells Pasadena Star-News.

An artistic rendering of the interplanetary space probe Voyager II as it flies by Jupiter.

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Dodd recently told the press that it would take a miracle for Voyager 1 to pull through, but the hardy little spacecraft and its twin sister Voyager 2 have survived a lot over the 46 years of their joint mission. And their engineering teams have found creative ways to keep the aging sister spaceships flying — and most importantly, to keep them sending new data home. Inverse talked with a Voyager engineer about what the team has learned from those years of jury-rigging solutions and how it might help other missions.

“In the last decade, I have learned from Voyager that there is (almost) always a way around a problem, no matter how dire it is,” Voyager mission assurance manager Bruce Waggoner tells Inverse. “You just have to think ‘outside the box’ when people tell you not to do so.”

Voyager 1 and Voyager 2 are on different trajectories out of the Solar System.

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Improvise, Adapt, Overcome

The team of engineers running the twin Voyager spacecraft have had to get increasingly creative over the last 46 years, as aging parts and systems have started to develop glitches and the power supply has begun to dwindle. Most of the people who designed the Voyagers and worked on the spacecraft in the early years of their mission have long since retired (and several have died), and they would probably be surprised by the ways today’s Voyager team has kept the pair of space probes running.

“Recently, the team found a way to keep the instruments powered for an additional 2 to 4 years by operating the spacecraft with an unregulated voltage,” says Waggoner. “This is a first as far as I know: operating the power system in a completely different way than the designers intended.”

The Voyagers’ designers built a safety mechanism to protect the instruments from sudden changes in the flow of electricity. If that happens, a regulator allows the spacecraft to access a small reserve of power, which is supposed to help it ride out the voltage fluctuation. But recently, Voyager engineers decided that after 45 years of the electrical systems working smoothly, Voyager 2 needed the extra power more than it needed the safety feature — because the alternative was shutting off one of Voyager 2’s instruments. (Voyager 1 is already down an instrument due to a hardware failure earlier in the mission, but its payloads will eventually face the chopping block, too.)

That kind of off-script improvisation has been the Voyager team’s standard operating procedure for decades.

“I would say that 100 percent of it has been figured out along the way,” Dodd told Inverse last year. “Absolutely nothing was known about flying for 45 years at 175 AU from us here on Earth, and we're into our 46th year now.”

And it’s been mostly trial and error. When something goes wrong with one of the Mars rovers, for instance, engineers can try out their solutions on a testbed: a replica of the spacecraft here on Earth kept on hand for exactly that purpose. But there is no Voyager testbed.

The goal is for each spacecraft to reach 19 billion miles away from the Sun with at least one instrument still running and communicating with Earth. Waggoner says the team has a 120-page book of ideas on how to keep the aging Voyagers working. Along the way, they’ve learned some tricks that may help extend the lives of future space missions.

An artist's impression of the Voyager 1 space probe flying past Saturn in the outer solar system, circa 1980.

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Keep the Spacecraft Simple

“Hopefully, people will look back at the lessons of Voyager and apply them,” says Waggoner. I work on many missions, and I use ideas from Voyager all the time, especially to think outside the box.”

Another key lesson is that it’s easier for a space mission’s engineering team to be flexible if the spacecraft itself is simple, study, and has backups for most of its hardware. The Flight Data System that’s currently on the fritz, for example, is Voyager 1’s backup; it's original one failed in 1981, and without redundancy, scientists would have missed 33 years of exploring the outer fringes of our Solar System.

Compared with more recent spacecraft, the Voyagers’ hardware is pretty bare-bones, its software is programmed in languages most modern engineers don’t even learn, and it sports about 64 kilobytes of memory (about 240,000 times less than the smartphone you’re probably reading this article on). But as strange as it sounds, that antique simplicity is actually one of Voyager’s biggest assets because it makes troubleshooting easier.

“I like the simpler code on Voyager because people can understand what the system will do, in most cases without simulation,” says Waggoner. That especially helps when trying to fix a pair of spacecraft with no testbeds here on Earth “just by thinking through the problems,” as Waggoner puts it.

Dodd, speaking to Inverse last year, compares operating the Voyagers to repairing an older-model car, compared with a more modern version with more complex systems and electronics.

“The simplicity of Voyager helps if you want to change things over time as the spacecraft gets older and the mission lasts longer,” says Dodd. “It's kind of like having an old car, and you can look under the hood and know what the key pieces are. When you have a new car, it's all driven by software and it's really hard to just go in there and tweak the carburetor and have it still run.”

Waggoner has a story about that, too. The Voyagers’ thrusters, which keep the distant spacecraft’s antennas pointed toward Earth, are slowly clogging with silicon dioxide. Last summer, it looked like the clogged thrusters could doom the missions within the next couple of years.

“Again, the team found workarounds by changing the way the thrusters are fired and pointing is managed,” says [source]. “Once the worst [clogged] thrusters fail, there may even be a way to allow the spacecraft to roll and return data.”

Of course, for Voyager 1, that depends on whether the spacecraft ever learns to speak again.

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