The Voyager 1 spacecraft is the farthest man-made object from Earth—ever. NASA recently confirmed that the 36-year-old space probe, currently hurtling 18.7 billion kilometers away from us, has officially left the solar system and entered interstellar space. How did NASA design a piece of technology that could survive such a mind-bendingly long journey? Suzanne Dodd, project manager for the Voyager mission, explained three strategies that give the Voyager probes (yes, there are two) their staying power.
I asked Dodd point blank: Is Voyager special, or just first? Could any NASA probe have crossed the heliopause into interstellar space, simply by aiming it in the right direction and waiting long enough? In short, no. "The Voyager project learned a lot from the Pioneer missions who went ahead of voyager to study Jupiter," Dodd says. "They found this very strong radiation environment at Jupiter that adversely affected the probe's electronics. Because of that, NASA added more shielding and redesigned some of the Voyager probes' components so that they could survive Jupiter's radiation."
Voyager 1 also packs the necessary instruments to sense if and when it did cross into interstellar space, which is not an obvious thing to determine. (That's why more than a year passed between the time that Voyager 1 actually left the solar system—on August 25, 2012—and NASA's confirmation of that fact.)
Obviously, NASA is not in the business of sending superfluous equipment into space. Every craft is designed to execute its primary mission as efficiently as possible. Still, Dodd acknowledges, In some important ways the older spacecraft are simpler." For one, Voyager 1's onboard computer has just 68 kilobytes of memory: 1/240,000th of the computing power in your smartphone, according to Dodd. That didn't seem so piddly back in 1976, when Voyager launched, but 36 years later, "there's a simplicity to it that lets you not get into trouble, especially when it comes to commanding and operating," she says. "You could make an analogy to a car. Nowadays the engines are all computerized and more likely to break down than an old car that you could just pop the hood and understand every piece of. That's important, since of course we can't take Voyager to the shop when something goes wrong."
And while Voyager's brain might be small, "a lot has changed on the ground," Dodd says. Voyager mission teams continue to use modern, up-to-date computing resources to creatively maximize Voyager's limited resources year after year. "There's not a day that goes by that we don't learn something new from it," she says.
3. Back up.
Redundancy and automation are a given in spacecraft design, especially when creating objects to explore environments that are literally alien. "Voyager was the first spacecraft to use onboard fault protection," says Dodd. "Without a command from the ground, it could sense the state that it was in, and turn something off if there was a problem. We are so far away: The roundtrip light time [for exchanging electronic signals] is over 34 hours, so you can't do anything in real time." Voyager also has a "backup mission" installed, which ensures that the craft will continue to execute and transmit science measurements if it doesn't receive command signals from Earth. "Voyager was one of the first probes to have this," Dodd says. "They're much more sophisticated now, but it was a big deal in the 1970s."
Voyager also has "two-string" redundancy for its critical systems, which simply means everything is doubled: "If the thrusters on the A side fail, we have the B side," Dodd explains. NASA has exploited this redundancy, along with Voyager's fault protection, to extend the craft's life decades beyond its original five-year mission to fly by Jupiter and Saturn. "There was always a hope that we could continue the mission into interstellar space, but nobody knew how far away 'interstellar space' actually was," Dodd says. "We've been turning off dual strings to save power over the decades. We're down to single string on everything." Still, Voyager 1 has enough juice to operate all of its instruments through 2020. "After that, we start turning off instruments," Dodd adds, "and by 2025 they'll all be off, so we won't get any more scientific data." But even then, Voyager 1 will continue transmitting basic tracking signals for another 10 years.
By 2036, when Dodd expects to finally lose contact with Voyager 1, the probe will have logged almost 60 years of continuous space travel. Of course, it will keep going on alone, at a 35-degree trajectory above the solar system's ecliptic plane—until someone or something discovers it, and its other meticulously designed piece of cargo.
[Images: Voyager via NASA]