NASA Shuts down a long-running experiment on Voyager 1

Voyager 1, the darling of deep space, is well into old age, coming up on the 50th anniversary of its launch and the first known thing from Earth to ever leave the solar system. The harsh side of that is Voyager 1 is running low on power and they're trying to keep the old girl going. Over the years, the solution to achieve a longer life has been to shut down old experiments and after much discussion, Voyager project leaders elected to shut down an experiment that has been gathering data since 1977 (with a few short interruptions).

On April 17, engineers at NASA’s Jet Propulsion Laboratory (JPL) in Southern California sent commands to shut down an instrument aboard Voyager 1 called the Low-energy Charged Particles experiment, or LECP. The nuclear-powered spacecraft is running low on power, and turning off the LECP is considered the best way to keep humanity’s first interstellar explorer going.

The LECP has been operating almost without interruption since Voyager 1 launched in 1977 — almost 49 years. It measures low-energy charged particles, including ions, electrons, and cosmic rays originating from our solar system and galaxy. The instrument has provided critical data about the structure of the interstellar medium, detecting pressure fronts and regions of varying particle density in the space beyond our heliosphere. The twin Voyagers are the only spacecraft that are far enough from Earth to provide this information.

The Voyager probes are powered by Radioisotope Thermoelectric Generators, RTGs, which run on small amounts of atomic decay from plutonium, turning the heat generated by the plutonium into electricity. Both Voyagers lose about 4 watts of power every year. The loss of power is something that was undoubtedly considered carefully during the design stages of the mission. All fuel sources run out, and plutonium RTGs are among the best for reliability and long life. After their close flybys in our solar system, the ground crews would order the turn off of power drains, like the video cameras, eventually becoming the only manmade objects to leave our solar system. After almost a half-century in space, the available power has dropped and the margins of "power available versus what you'd like" have grown razor thin, requiring the team to conserve energy by shutting off heaters and instruments while making sure the spacecraft don’t get so cold that their fuel lines freeze.

During a routine, planned roll maneuver on Feb. 27, Voyager 1’s power levels fell unexpectedly. Mission engineers knew any additional drop in power could trigger the spacecraft’s undervoltage fault protection system, which would shut down components on its own to safeguard the probe, requiring recovery by the flight team — a lengthy process that carries its own risks.

The Voyager team needed to act first.

“While shutting down a science instrument is not anybody’s preference, it is the best option available,” said Kareem Badaruddin, Voyager mission manager at JPL. “Voyager 1 still has two remaining operating science instruments — one that listens to plasma waves and one that measures magnetic fields. They are still working great, sending back data from a region of space no other human-made craft has ever explored. The team remains focused on keeping both Voyagers going for as long as possible.”

Years ago, the project managers put together a plan of what to shut down, when to shut it down, in the correct order.

Of the 10 identical sets of instruments that each spacecraft carries, seven have been shut off so far. For Voyager 1, the LECP was next on that list. The team shut off the LECP on Voyager 2 in March 2025.

While the Voyagers are beyond our solar system, and among the fastest things mankind has ever launched, they're not remotely close to the next star system. That's in the vicinity of four light years away, while the Voyagers are barely one light day away. Still, that makes sending instructions to the probes inconvenient at best. That means being really sure the message you're sending is thoroughly tested to know it's correct and once transmitted, the soonest you can know if it worked is another day away. 

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

Engineers are confident that shutting down the LECP will give Voyager 1 about a year of breathing room. They are using the time to finalize a more ambitious energy-saving fix for both Voyagers they call “the Big Bang,” which is designed to further extend Voyager operations. The idea is to swap out a group of powered devices all at once — hence the nickname — turning some things off and replacing them with lower-power alternatives to keep the spacecraft warm enough to continue gathering science data.

The team will implement the Big Bang on Voyager 2 first, which has a little more power to spare and is closer to Earth, making it the safer test subject. Tests are planned for May and June 2026. If they go well, the team will attempt the same fix on Voyager 1 no sooner than July. If it works, there is even a chance that Voyager 1’s LECP could be switched back on.

I'm not sure what they mean by "about a year of breathing room." Voyager 2 launched on August 20, 1977 with Voyager 1 following 16 days later on September 5. They're closing in on their 49th year in space this coming August and early September with the 50th anniversary the following year. I've been hoping they'd make 50 years for as long as I can remember.