Nearly 50 years after launch, NASA has executed a power-system swap on Voyager 2, successfully trading fading plutonium heat for about 10 watts of preserved power and extending the spacecraft’s science mission by at least an extra year.
Voyager 2 has no repair port, no nearby spare, and no technician capable of reaching its 1970s hardware. Nearly 49 years after its initial liftoff on August 20, 1977, every intervention requires commands transmitted across more than 20 billion kilometers, followed by a wait of nearly two days just to find out whether the distant spacecraft accepted the instructions.
This July, engineers at NASA’s Jet Propulsion Laboratory used that narrow connection to rearrange Voyager 2’s power and thermal systems. The coordinated procedure, nicknamed the Big Bang
by engineers, freed almost 10 watts and postponed the need to shut down another active science instrument.
Radioisotope Power Decay and the Four-Watt Annual Loss
The root of the spacecraft’s predicament lies in how it generates electricity. Voyager 2 launched with three radioisotope thermoelectric generators, or RTGs. These units are not nuclear reactors and do not rely on chain reactions; instead, heat from the natural decay of plutonium-238 crosses thermoelectric materials to convert part of that temperature difference into electrical current.
The setup operates without sunlight or moving parts, enabling a grand tour past all four giant planets and out into interstellar space. Yet it weakens continuously. NASA reports that each Voyager spacecraft loses about 4 watts of available electrical power every year as the plutonium supply decays and aging thermoelectric converters lose efficiency.
That annual reduction was easy to absorb when the probes possessed hundreds of watts to distribute. With almost half a century of decline behind them, a few watts can decide whether an instrument continues to function. Mission controllers have spent years shedding loads by retiring cameras and instruments meant strictly for planetary encounters and turning off heaters, sometimes running equipment far below tested thermal limits.
The Thermal Puzzle of the Big Bang Power Rewrite
Despite its dramatic moniker, the Big Bang did not increase the total output of the RTGs. Instead, it altered which onboard devices consumed the shrinking supply. A mission update detailed powered devices being switched off while lower-power alternatives were substituted simultaneously, designed to reduce demand without letting critical components freeze.
This requirement turns an ordinary power-saving exercise into a delicate thermal puzzle. Almost every active electrical device produces waste heat. A recorder, sensor, or propulsion component warms its compartment regardless of its primary function. Turning off a load may save electricity yet remove vital warmth from a propellant line located just centimeters away.
Voyager’s attitude-control thrusters rely on hydrazine to keep the high-gain antenna pointed toward Earth so controllers can send commands and receive data. If the fuel lines freeze or a thruster branch becomes unusable, the spacecraft loses its ability to point home. Engineers previously managed this balance during a 2024 Voyager 1 thruster swap that borrowed power from a main heater to warm a dormant branch.
Swapping Recorders and Heaters for Interstellar Survival
According to detailed accounts, engineers turned off an old digital tape recorder and two heaters, while simultaneously powering two different heaters and a propulsion instrument. The new combination uses nearly 10 watts less while directing useful warmth to places that still require it.
The retirement of the tape recorder marks a significant milestone in the mission’s evolution. During the planetary tour, it stored high-rate observations for later transmission. In the interstellar mission, most science returns at lower rates through the Deep Space Network, turning the recorder’s electrical demand and heat output into a target for survival cuts.
Removing old loads without adding replacements could have created dangerous cold spots, while adding replacements first could have pushed the power bus below safe operational margins. Testing the sequence took months because failure could be final, compounded by the fact that Voyager 2’s only command-capable ground antenna—the 70-meter dish at Canberra—was unavailable for upgrades.
Next Steps for the Twin Interstellar Explorers
Before this operation, Voyager 2 was projected to lose one of its three remaining science instruments by the end of 2026. The conserved power is now expected to keep those three instruments operating for at least one additional year.
The mission team intends to apply the identical power-saving swap to Voyager 1, which is located even farther from Earth than its twin. Engineers plan to complete that corresponding effort in the coming months as the probes push deeper into the unknown.
