NASA’s farthest space explorers, the Voyager spacecraft, are showing signs of wear after nearly five decades in the harsh environment of space. In an effort to preserve energy, officials have decided to deactivate one instrument on each of these veteran probes.

Launched in 1977, the twin Voyager probes embarked on their journey during a rare alignment of the outer planets that occurs every 176 years. Originally tasked with exploring these planets, their mission was completed in just over a decade. However, the Voyagers continue their mission, with Voyager 2 now over 13 billion miles from Earth and Voyager 1 over 15.5 billion miles away. Their current mission involves studying the interstellar medium, which lies beyond the sun’s influence.

Moving forward, each spacecraft will operate with one less instrument, as announced by NASA on March 5. The cosmic ray subsystem experiment on Voyager 1 was shut down on February 25, and the low-energy charged particle instrument on Voyager 2 is scheduled for deactivation on March 24. These instruments were designed to measure high-speed charged particles, including cosmic rays, ions, and electrons, in the vastness of interstellar space. The decision to turn these instruments off was made to conserve the dwindling power supplies of the spacecraft.

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“The Voyagers have been standout performers in deep space since their launch, and we aim to maintain their operation for as long as feasibly possible,” stated Suzanne Dodd, Voyager project manager at NASA’s Jet Propulsion Laboratory, in a March 5 announcement. “However, we’re facing a critical power shortage. Without shutting down an instrument on each spacecraft now, we’d likely only have a few months left before potentially having to end the mission.”

Additionally, NASA plans to deactivate Voyager 1’s low-energy charged particle instrument and Voyager 2’s cosmic ray subsystem in 2026. Their objective is to keep at least one instrument operational on each spacecraft into the 2030s.

Each Voyager was equipped with a nuclear power source containing plutonium at launch, a decision based on the understanding that the probes would venture too far from the sun for solar power to be feasible. Nonetheless, each year, the power output from these plutonium sources decreases by about four watts, roughly the output of a small light bulb.

The spacecraft require power for their computers, communication systems, and scientific instruments. This forces mission scientists to make difficult decisions about which instruments to keep running and which to sacrifice to save energy, as losing power completely would mean the premature end of the mission.

The Voyager spacecraft have become icons of space exploration. Voyager 2 was the first to launch, followed by Voyager 1 three weeks later, which quickly moved ahead. Voyager 1 passed Jupiter in 1979 and Saturn and its largest moon, Titan, in 1980. Voyager 2 took its turn observing Jupiter in 1979 and Saturn in 1981, subsequently becoming the first and only spacecraft to fly by Uranus and Neptune in 1986 and 1989, respectively.

After their planetary missions were complete, both spacecraft remained in good health and continued their journey. They explored the outer limits of the sun’s influence and then, in 2012 and 2018 respectively, entered interstellar space, providing humanity with unprecedented close-up observations of the cosmos beyond our solar system. Currently, Voyager 2 is nearly 140 times as far from the sun as Earth, and Voyager 1 is 166 times as distant.

Communicating with these distant probes is challenging; it takes 19.5 hours for a signal to reach Voyager 2 and over 23 hours for Voyager 1. This makes troubleshooting a slow and meticulous process. Recently, Voyager 1 experienced a significant communication issue beginning in November 2023, resulting in the collection of only partial data in early 2024, while Voyager 2 encountered a couple of weeks of communication blackout in 2023.

Despite these challenges, the efforts to maintain the Voyagers are worthwhile. “Every minute of every day, the Voyagers journey into uncharted regions where no spacecraft has ventured before,” said Linda Spilker, Voyager project scientist at JPL. “This means each day could potentially be their last, but it also holds the possibility of a new interstellar discovery. We’re committed to extending their groundbreaking journey for as long as possible.”