Last Month NASA Shut Off Three Devices Aboard Voyager 2 — and Turned On Three Others in the Same Instant — Woody Magazine, Aug. 18, 2026

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Aug. 18, 2026 (Tue.)

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Last Month NASA Shut Off Three Devices Aboard Voyager 2 — and Turned On Three Others in the Same Instant

It was a command that could not be taken back.

On July 9 a command left NASA's Jet Propulsion Laboratory. Its destination was Voyager 2, launched in 1977 and now more than 13 billion miles from Earth. A radio signal needs close to twenty hours to cross that distance. An answer needs twenty more.

The instruction was short. Switch off three devices, and in the same instant switch on three others.

When power runs short you turn off whatever you are not using. That is what saving looks like almost everywhere, and nearly always it is the right move. This team turned three things off and three things on — not one at a time but together, in a sequence with no undo. The team called the operation the Big Bang. On August 4 NASA announced that it had worked.

One of the devices they shut off was a tape recorder

Voyager carries a digital tape recorder, an eight-track machine built to 1977 specifications. Its job was to hold science data on magnetic tape until the spacecraft could send it home.

That is not why it was running this summer. A NASA spokesperson told The Register that the recorder had been left on because “its residual heat was in the right location.” It also drew less current than the dedicated heater sitting beside it.

Which does sound like an oversight, and it is easy to read it that way. A tape machine from 1977, spinning for nothing. But picture the old desktop computer somebody leaves running in a cold room all winter. Switch it off to save electricity and the room gets noticeably cooler. The current that machine was drawing never went anywhere. It became heat.

On Voyager, the power bill and the heating bill are one bill

Voyager does not run on solar panels. Out at the distances these probes now fly, there is not enough sunlight left to work with. Each probe instead carries radioisotope thermoelectric generators. Plutonium-238 decays on its own and gives off heat. That heat crosses a temperature gradient in a bank of solid-state junctions, and a fraction of it comes out the other side as electricity. Nothing spins. There is nothing to jam or seize. That is how the design has lasted nearly forty-nine years.

It is also why the decline cannot be reversed. Plutonium-238 has a half-life of 87.7 years, so each year it yields a little less. NASA puts the loss at roughly four watts a year per spacecraft. The plutonium is not the only thing fading, either. The junctions that turn its heat into current lose efficiency as they age, and NASA's planetary data archive lists both causes side by side. No repair recovers any of it. For half a century the flight team's real job has been to keep deciding where a shrinking supply should go.

Here the desktop computer comes back. In a house you switch the computer off and nudge the thermostat up, because electricity and heating arrive on separate bills. Voyager has one bill. The current that runs a heater, the current that ran the recorder, and the current that aims the antenna all come from the same generators. All of it turns into heat on the way through. And in a vacuum there is no air to carry that heat off. It leaves only by radiating.

So spending less power on Voyager means heating less. The saving and the loss are the same motion.

What freezing actually ends

Cold electronics failing is the obvious worry. It is not the one that keeps the flight team awake. That would be the fuel lines.

Voyager still uses hydrazine thrusters, firing in small pulses to hold its high-gain antenna on Earth. Let the lines carrying that fuel freeze and the thrusters are finished. Without thrusters the spacecraft cannot hold its attitude. Without attitude control the antenna drifts off Earth. From that moment the probe can neither hear a command nor send a byte home, and the mission is over.

This is why the NASA spokesperson bothered to specify that the replacement devices had to keep the fuel lines warm. Switching off a heater out there is not a decision to give up a component. It is a decision to accept some chance of losing the spacecraft. Frozen lines do not thaw back into service.

So why not simply add heat? Heaters draw power, and the power comes out of the one bill.

Not a saving. A swap.

Here is what actually happened on July 9. The team shut off two dedicated heaters and the tape recorder. In the same instant it switched on two different heaters and one more device that throws off usable warmth. The new set keeps the same places warm on less current.

It is the household version of unplugging the computer and sliding an electric blanket into its place. The spots that have to stay warm still do. Only the meter slows down.

about 10 watts

The reduction in demand, on a spacecraft that loses roughly four watts a year.

Doing it all at once was not for show. Do it in sequence and something, somewhere, drops below its minimum temperature during the gap. The new configuration had to satisfy every thermal floor from the first moment it existed. NASA told The Register that the team had made trades like this before, but usually one device for one device. Six at once was new, and the nickname followed from that.

The plan came together over late 2025 and early 2026. For much of that stretch, the one ground antenna that could reach Voyager 2 was down for repairs, so the team had months with nothing to do but check the arithmetic.

In May the team ran a power test to confirm the new set would not pull too much current. The numbers landed where they were supposed to, and the swap went ahead in July. Kareem Badaruddin, who manages the Voyager mission at JPL, said the results tracked the predictions closely enough that the team finished without revising the plan.

“almost everything functions as a heater, no matter what it was designed to do” Kareem Badaruddin, Voyager mission manager, NASA Jet Propulsion Laboratory, to Scientific American

What ten watts buys

Voyager 2 launched carrying ten science instruments. Three are still collecting: a magnetometer, a plasma wave subsystem, and a cosmic ray subsystem. Only the Voyagers are measuring those values from inside interstellar space. Without this swap, one of the three would have had to go dark before the end of 2026. NASA now says the savings buy at least another year.

The generators did not gain a watt. The plutonium is cooling at exactly the rate it was cooling in June. What the team found was not new power but a cheaper arrangement of the heat it was already making.

Voyager 1 is in worse shape. During a roll maneuver on February 27, its power fell further than anyone expected. Engineers had to move before the undervoltage protection kicked in and began shutting components down without asking. On April 17 they switched off the Low-Energy Charged Particles instrument. They deliberately left its half-watt stepper motor running, which keeps the door open to reviving the instrument if power ever turns up. Voyager 1's own swap follows in the coming months.

The day after tomorrow Voyager 2 turns forty-nine. The team was never choosing what to spend less on. It was working out what each expense had quietly been holding up. On the ledger the recorder looked like waste. It was a furnace.

In Three Lines

Voyager's generators turn plutonium heat into electricity, and that electricity turns back into heat as it passes through the spacecraft. Cutting power cuts heating along with it.
The three devices switched off on July 9 were two heaters and a digital tape recorder that had been running for its warmth rather than its data.
The swap freed about ten watts and pushed the next instrument shutdown back by at least a year. Generator output did not rise at all.

Sources

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