Nearly 50 years after their late-summer 1977 launches, NASA’s twin Voyager probes are continuing their journey in interstellar space while confronting a steadily shrinking power supply. Each spacecraft relies on radioisotope thermoelectric generators, which produce electricity by converting heat released from the natural radioactive decay of plutonium-238. Because this plutonium isotope decays toward its 88-year half-life, less heat is emitted over time. Consequently, each Voyager spacecraft loses about 4 watts of available electrical power every year.
Fading Power and Aging Hardware in Interstellar Space
Operating in interstellar space more than 15 billion miles, or about 24 billion kilometers, away from Earth, the probes feature 1970s hardware with no repair ports or spare spacecraft waiting nearby. Every intervention by engineers at NASA’s Jet Propulsion Laboratory requires transmitting commands across more than 20 billion kilometers, followed by a wait of nearly two days to determine whether the spacecraft has accepted the instruction. With margins growing razor-thin after almost half a century of decline, a few watts can determine whether an instrument survives.
The Big Bang
Power-Saving Strategy
To stretch the fading power supply, JPL engineers devised a coordinated procedure nicknamed the Big Bang.
According to Voyager mission manager Kareem Badaruddin, the maneuver is the most important thing we’ve done on the Voyager spacecraft in decades.
The operation does not increase the output of the thermoelectric generators; instead, it changes which onboard devices consume the shrinking electrical supply by simultaneously switching off certain powered devices and substituting lower-power alternatives.
Specifically, the maneuver switches off two heaters and an old-school, eight-track tape recorder used by the digital Data Tape Recorder system, while carefully turning on two other heating units and one of the craft’s onboard propulsion systems. This coordinated approach saves the probe almost 10 watts per year without sacrificing essential hardware to the cold. Because Voyager 2 was closer to Earth and had more power available, engineers tested the stunt on Voyager 2 first. The successful test freed almost 10 watts, postponing the need to shut down another science instrument and keeping the probe’s three remaining instruments operating for at least an extra year.
Instrument Shutdowns and Future Outlook
Both Voyagers originally launched with 10 instruments apiece. Many were retired years ago after serving their purpose during the planetary encounters of the solar system’s Grand Tour.
However, ongoing power declines have forced further cutbacks. In 2025, a JPL power plan switched off an instrument on each probe, and a routine roll maneuver on February 27 caused an unexpected drop in power on Voyager 1 that threatened to trigger its undervoltage fault protection system.
To prevent an automated shutdown, engineers at JPL sent commands on April 17 to shut down Voyager 1’s Low-energy Charged Particles experiment, or LECP. While shutting down science instruments is not preferred, the long-planned strategy ensures systems shut down in a predetermined order. Seven sets of instruments have now been shut off on each spacecraft. For Voyager 1, the LECP shutdown took about three hours and 15 minutes, following a roughly 23-hour communication transit time across more than 15 billion miles. A small motor that rotates the LECP sensor was left running on 0.5 watts to maintain the possibility of restarting the instrument if extra power becomes available in the future.
Following the successful testing on Voyager 2, mission managers intend to apply the Big Bang
power-saving swap to Voyager 1 in the coming months. Project manager Suzanne Dodd previously stated that Voyager 1 would definitely
reach its 50th anniversary on September 5, 2027, and might even continue into the 2030s if the mission gets really lucky.
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