Voyager 2 cannot make more electricity. Its radioisotope generators have been fading since launch in 1977, and no solar panel, battery recharge or repair crew can reverse that decline. Yet engineers have found a way to stretch the probe’s remaining power by changing which devices consume it and where their waste heat goes.
The operation was nicknamed the “Big Bang” because several changes had to happen together. Planning and testing occupied the first half of 2026, while the complete six-device swap was carried out on 9 July. According to NASA’s mission update, it freed nearly 10 watts and should keep Voyager 2’s three surviving science instruments operating for at least one additional year.
The source is shrinking by about four watts a year
Voyager 2 launched on 20 August 1977 with three radioisotope thermoelectric generators, or RTGs. These are not nuclear reactors. Heat from the natural decay of plutonium-238 passes through thermoelectric materials that convert part of the temperature difference into electricity. The design has no moving parts and does not depend on sunlight, which made it suitable for a journey past all four giant planets and into interstellar space.
It also becomes weaker continuously. NASA estimates that each Voyager loses about four watts of available electrical power each year as plutonium decay reduces the heat supply and ageing thermoelectric converters lose efficiency. Four watts was modest when the probes had hundreds to distribute. After almost half a century, it can decide whether an instrument stays on.
Controllers have spent decades retiring loads that no longer serve the interstellar mission. Cameras and other instruments built for the planetary encounters went first. Heaters were switched off, sometimes leaving hardware to function far below its original test temperatures. A 2025 JPL power update described the shutdown of another instrument on each probe. Without a new saving, Voyager 2 was expected to lose one of its three remaining instruments before the end of 2026.
The power budget is also a heat map
The Big Bang did not alter the RTGs. Instead, it changed the pattern of demand. That distinction matters because almost every powered component produces waste heat. A recorder or sensor may warm nearby plumbing even when its primary function is no longer important. Switching it off saves electricity but can expose a propellant line or another critical component to dangerous cold.
Voyager 2’s hydrazine thrusters control the spacecraft’s attitude and keep its high-gain antenna pointed towards Earth. If a fuel line freezes or a thruster branch becomes unusable, the probe could lose the orientation needed to receive commands and return data. The team had already used smaller power-saving measures, including a 2023 strategy that drew on a voltage regulator’s reserve. The 2026 plan demanded a broader rearrangement of both electricity and heat.
According to a detailed Scientific American account, engineers switched off an old digital tape recorder and two heaters. At the same time, they powered two different heaters and a propulsion-related device. The replacement combination consumes nearly 10 watts less while moving useful warmth towards the places that still require it.
The tape recorder illustrates the trade-off. During the planetary tour it stored high-rate observations for later transmission. Voyager 2’s present measurements can generally be sent at lower rates through the Deep Space Network, but the recorder’s heat had become part of the spacecraft’s thermal balance. Removing that load without adding replacements could have created cold spots. Adding the replacements first could have consumed power the bus did not have. “All at once” meant moving from one stable state to another without lingering in an unsafe one.
Early planning led to a July 9 switch
The headline’s “early 2026” describes when the reconfiguration campaign was being developed, not when Voyager 2 completed the full manoeuvre. Engineers began planning in late 2025 and early 2026, then ran separate power and thermal tests in May and June. The complete three-off, three-on command sequence was executed on 9 July 2026.
Testing could not remove every risk. The coldest points in Voyager 2’s propellant lines are not directly instrumented because the original mission was never designed for this situation. Engineers instead rely on old drawings, thermal models and the behaviour of neighbouring components. Those models must represent hardware whose materials and electronics have aged for nearly five decades.
Distance stretches every decision. A radio command takes about 20 hours to reach Voyager 2, and telemetry needs roughly the same time to return. A single troubleshooting exchange can therefore occupy most of two days before analysis begins. As ScienceBlog has previously reported, only the 70-metre Deep Space Network antenna near Canberra can transmit commands to Voyager 2. There is no physical inspection if a relay sticks and no quick recovery if the spacecraft loses its Earth-pointing attitude.
What the saved watts keep measuring
The operation preserved Voyager 2’s magnetometer, plasma wave subsystem and cosmic ray subsystem. Together they measure the local magnetic field, infer plasma conditions from oscillations and track energetic particles from the galaxy and solar system. These are not observations that an orbiter near Earth can reproduce.
Voyager 2 crossed the heliopause in 2018, entering the interstellar medium six years after Voyager 1. The probes travel in different directions, so they sample different parts of the boundary between the Sun’s protective bubble and surrounding galactic space. No other working spacecraft has crossed that boundary. Retiring one instrument would end a measurement stream with no immediate replacement.
The successful operation also provides a path for Voyager 1. NASA said in August that the team intended to perform a similar reconfiguration on the more distant probe in the coming months. Success on Voyager 2 does not make that later operation automatic. The two spacecraft have followed different thermal and operational histories, and each has its own ageing components and margins.
Nearly 10 watts are not 10 new watts
At the Voyagers’ typical decline of about four watts a year, a saving of nearly 10 watts looks arithmetically equivalent to roughly two and a half years. NASA makes the more conservative claim that all three instruments can remain on for at least one extra year. Scientific American reported that the team hopes the benefit may approach two years. The difference reflects uncertainty, not contradiction.
Power decay is only one variable. Heater duty cycles change, components age, thermal conditions shift as other devices are retired and an unrelated fault could end the mission first. The saving postpones the next instrument shutdown; it does not guarantee that the entire spacecraft will operate for a fixed number of additional months.
Nor does the next shutdown necessarily mean immediate silence. Voyager 2 may continue returning data with two instruments and eventually one, provided it can still power its computers, radio and attitude control. The spacecraft was built with extensive redundancy, but redundancy cannot replace energy that no longer exists.
The Big Bang was therefore an exercise in subtraction. It did not refill a nuclear battery, reverse radioactive decay or generate a single extra watt. Engineers found a lower-demand route through a heat map that nobody expected them to manage in 2026. On a probe too distant to touch, keeping three unique science instruments alive for at least another year is the result.