Scientists hope to keep the two spacecraft operational into the 2030s.

On 25 February, engineers at NASA’s Jet Propulsion Laboratory (JPL) in Southern California deactivated the cosmic ray subsystem experiment aboard Voyager 1. They also scheduled to shut down Voyager 2’s low-energy charged particle instrument on 24 March.

These steps are part of ongoing efforts to manage the gradually diminishing power supply of the twin probes. Despite these reductions, three science instruments will remain operational on each spacecraft.

Launched in 1977, Voyagers 1 and 2 rely on a radioisotope power system that converts the heat from decaying plutonium into electricity. However, their power supply decreases by about 4 watts per year.

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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. 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.” said Suzanne Dodd, Voyager project manager at JPL, in a statement on the NASA blog.

An illustration of where Voyager 2 was in 2024. Credit: Space.com

Each spacecraft was originally equipped with 10 science instruments, some of which were turned off after completing planetary flybys. The remaining active instruments focus on studying the heliosphere—a protective bubble of solar wind and magnetic fields created by the Sun—and interstellar space beyond it.

Voyager 1 crossed the heliosphere’s boundary in 2012, followed by Voyager 2 in 2018. No other human-made spacecraft has ever operated in interstellar space.

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To conserve power, Voyager 2’s plasma science instrument—used to measure electrically charged atoms and their movement—was turned off last October. It had been collecting only limited data due to its orientation. Voyager 1’s plasma science instrument was shut down years earlier due to performance degradation.

Interstellar legacy

The cosmic ray subsystem deactivated on Voyager 1 last week consists of three telescopes designed to study cosmic rays, including protons from the Sun and the galaxy, by measuring their energy and flux. Data from these telescopes played a key role in determining when and where Voyager 1 exited the heliosphere.

Voyager 2’s low-energy charged particle instrument, scheduled for shutdown later this month, measures various ions, electrons, and cosmic rays from our solar system and beyond. It includes two subsystems: the low-energy particle telescope, which provides broad energy measurements, and the low-energy magnetospheric particle analyzer, which focuses on magnetospheric studies.

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Both subsystems rely on a rotating platform powered by a stepper motor that delivers a 15.7-watt pulse every 192 seconds. Initially tested for 500,000 steps—sufficient for operation through the spacecraft’s Saturn encounter in 1980—the motor will have completed more than 8.5 million steps by the time it is deactivated on Voyager 2.

NASA has long sought to avoid shutting down science instruments, given the unique data provided by the Voyager probes. With the latest power-saving measures, the spacecraft should remain operational for about a year before another instrument must be turned off.

Voyager 1 will continue running its magnetometer and plasma wave subsystem. Its low-energy charged particle instrument will remain active until the end of 2025 before being shut down next year. Voyager 2, meanwhile, will keep its magnetic field and plasma wave instruments active for the foreseeable future. Its cosmic ray subsystem is scheduled for shutdown in 2026.

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Thanks to this power conservation strategy, engineers estimate that at least one science instrument on each probe could continue operating into the 2030s. Unless unforeseen challenges arise to shorten their lifespan, given the Voyagers' 47-year journey through deep space.

Voyager 1 and Voyager 2 remain the most distant human-made objects ever built. Voyager 1 is currently over 25 billion kilometers away, while Voyager 2 is more than 21 billion kilometers from Earth. For comparison, our planet is approximately 150 million kilometers from the Sun.

Due to their extreme distance, it now takes over 23 hours for a signal to reach Voyager 1 and 19.5 hours for Voyager 2.

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