NASA engineers have come up with a power-saving strategy to eke more time—and more science—out of the Voyager probes, humanity’s longest-running spacecraft, as they continue venturing into unexplored reaches of interstellar space.
And time is of the essence: Voyager 1 and 2 have been flying since 1977, and their power sources have been gradually fading, putting their instruments at risk. Out in the vast abyss of deep space, unfathomably far from our sun, solar power isn’t viable. That’s why engineers equipped each Voyager with a trio of radioisotope thermoelectric generators, or RTGs. These work by converting the heat from the decay of radioisotope fuel, plutonium-238, into electricity. They’re basically nuclear batteries—and they’re finally running out of juice, losing a predictable 4 watts per year. While the Voyagers don’t need that power for propulsion, it’s essential to their ability to collect scientific readings of far-flung charged particles and magnetic fields—so far, humanity’s only opportunity to sample that data in interstellar space.
A couple of years ago, NASA began exploring ways to keep the Voyagers’ instruments running as long as possible. The first move, in 2019, was to start turning off the heaters for the science instruments. That worked; the devices kept working despite temperatures dropping some 50 degrees Celsius, much colder than the conditions they’d been tested in. But it still wasn’t enough, so at the end of March, a NASA team initiated an energy-saving strategy on Voyager 2 that dips into some reserve power meant to protect systems from voltage spikes.
While this strategy does leave the craft more vulnerable, the risk of such spikes seems to be very low, says Suzanne Dodd, the Voyager project manager at NASA’s Jet Propulsion Laboratory in Southern California. Assuming all goes well, they’ll start similar voltage management on Voyager 1 as early as this fall. Altogether, Dodd thinks this could buy the probes’ science mission a few extra years. Voyager is still a mission of discovery, she says, and every piece of data the spacecraft obtain in interstellar space is valuable. “I continue to be amazed by these spacecraft and by the engineers who come up with clever ways to operate them,” says Dodd.
Now 45 years old, the Voyagers spent their first two decades flying through the solar system, snapping photos of Jupiter, Saturn, Uranus, and Neptune as they zoomed by. Voyager 1 also captured the iconic “pale blue dot” photograph of a tiny, distant Earth. As they kept going, they continued capturing data. They have long outlived their predecessors, Pioneer 10 and 11, which were the first probes to fly by the gas giants but shut down more than 20 years ago. Both Voyagers have flown well beyond the Kuiper belt, a region hosting Pluto and other small, icy bodies. In 2012, Voyager 1 left the heliosphere, the protective bubble of particles and magnetic fields generated by the sun, beyond which lies the interstellar medium. Its twin followed six years later, at which point both were officially in interstellar territory, cruising at 35,000 miles per hour into the unknown.
Today, Voyager 1 is 159 astronomical units from home, and Voyager 2 is at 133 AU, traveling in a different direction. (1 AU is the distance between the Earth and sun, or about 93 million miles.) The spacecraft are surely showing signs of age—the team dealt with telemetry problems on Voyager 1 last year—but the cosmic workhorses are continuing on.