NASA’s Voyager Probes Lose One Instrument Each as Power Wanes
NASA’s twin Voyager probes, which launched in 1977, are the longest-running missions to send data home. But as their power supplies wane, scientists are saying goodbye to one instrument on each spacecraft
NASA’s most distant observers are losing steam as the toll of spending nearly five decades in space adds up. Scientists have announced that they will turn off one additional instrument on each spacecraft to conserve energy.
The twin Voyager probes launched in 1977 to take advantage of a once-in-176-year alignment of the outer planets. That task wrapped up within a little more than a decade, but still the spacecraft trek outward: currently, Voyager 2 is more than 13 billion miles from Earth, and Voyager 1 is more than 15.5 billion miles away. At this point, the Voyagers are tasked with studying the interstellar medium found beyond the influence of the sun.
Scientists will have observations from one less instrument on each spacecraft moving forward, however, NASA officials announced on March 5. Mission managers turned off Voyager 1’s cosmic ray subsystem experiment on February 25, the agency wrote, and will do the same for Voyager 2’s low-energy charged particle instrument on March 24. These instruments observe fast-moving charged particles called cosmic rays, as well as ions and electrons, in interstellar space. Both deactivations are purposeful energy-saving measures.
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“The Voyagers have been deep space rock stars since launch, and we want to keep it that way as long as possible,” said Suzanne Dodd, Voyager project manager at NASA’s Jet Propulsion Laboratory (JPL), in the March 5 statement. “But electrical power is running low. If we don’t turn off an instrument on each Voyager now, they would probably have only a few more months of power before we would need to declare end of mission.”
NASA officials have also decided that, in 2026, they will turn off Voyager 1’s low-energy charged particle instrument and Voyager 2’s cosmic ray subsystem, according to the statement. Their goal is to ensure that at least one instrument on each spacecraft remains operational into the 2030s.
Each Voyager spacecraft launched with a nuclear power source made of plutonium. It was the sensible choice—engineers knew all along that the probes would be traveling much too far from the sun to rely on solar power. Each spacecraft’s plutonium core produces a little less juice each year, however—annually losing about four watts, equivalent to a low-power light bulb.
The spacecraft’s computer, communications system and instruments all require energy to operate, so scientists are faced with a tough choice: hand select where to save power by sacrificing particular instruments or risk overdrawing the power supply and losing the whole spacecraft. And no one wants to see either Voyager end any earlier than it has to.
The Voyager spacecraft are iconic. Voyager 2 launched first; three weeks later Voyager 1 followed suit and zipped ahead. Voyager 1 flew past Jupiter in 1979 and past Saturn and its largest moon, Titan, in 1980. Voyager 2 followed suit, observing Jupiter in 1979 and Saturn in 1981, and then became the first and so far only spacecraft to ever fly past Uranus or Neptune, respectively doing so in 1986 and 1989.
At that point the vehicles had run out of planets to observe, but both were still essentially healthy—so NASA decided to follow along for the ride. The Voyagers explored the outer reaches of the sun’s influence. Then, in 2012 and 2018, respectively, each entered interstellar space, giving scientists the first-ever close-up observations of the cosmos beyond our solar system. Today Voyager 2 is nearly 140 times as far from the sun as Earth is, while Voyager 1 is 166 times as far.
A signal from Earth takes 19.5 hours to reach Voyager 2 and more than 23 hours to reach Voyager 1, making any troubleshooting for the probes a painfully slow process. And there has been a lot of troubleshooting recently. Voyager 1 spent early 2024 collecting only partial data after a serious communications issue began in November 2023, for example, while Voyager 2 was unable to communicate with Earth for a couple of weeks in 2023.
But for NASA, the troubleshooting is well worth it. “Every minute of every day, the Voyagers explore a region where no spacecraft has gone before,” said Linda Spilker, Voyager project scientist at JPL, in the recent statement. “That also means every day could be our last. But that day could also bring another interstellar revelation. So, we’re pulling out all the stops, doing what we can to make sure Voyagers 1 and 2 continue their trailblazing for the maximum time possible.”
