NASA is keeping Voyager 1 alive by switching off instruments and heaters one by one—but it cannot let the spacecraft become so cold that its fuel lines freeze. If those lines fail, Voyager could lose the thrusters that keep its antenna aimed at Earth, permanently silencing the most distant human-made object.

Nearly half a century after it left Earth, Voyager 1 is being kept alive one switch at a time. Its power supply fades a little every year, so mission engineers at NASA have been turning off instruments and heaters in a careful sequence, trading capability for time. But the trimming has a hard floor. If the spacecraft is allowed to grow too cold, the lines that carry its fuel could freeze, and that would threaten the small thrusters that keep its antenna pointed at Earth. Lose those, and the most distant human-made object falls silent for good.

It is a slow, deliberate piece of triage, carried out across more than 25 billion kilometres.

A power supply that only shrinks

Voyager 1 does not run on sunlight. At its distance the Sun is just another bright star, so the spacecraft draws electricity from a radioisotope thermoelectric generator, which turns the heat of decaying plutonium into power. That heat source cools a little every year, and the spacecraft loses roughly four watts of available power annually. After 48 years, the margin left to work with is very thin.

So the team spends power like a dwindling bank balance. Of the ten identical instrument packages the Voyagers carry, seven have now been switched off. The most recent went dark on 17 April 2026, when engineers shut down Voyager 1’s low-energy charged-particle instrument. Two science instruments are still running on the spacecraft, one that listens to plasma waves and one that measures the magnetic field. The order of these shutdowns was not improvised. Years ago the science and engineering teams sat down and agreed a sequence, deciding which parts to give up first so the mission could keep returning useful data for as long as possible.

The cold that cannot be allowed

Every instrument and heater switched off saves power, but it also lets part of the spacecraft get colder. That is the constraint the title points to. Voyager steers and orients itself with small thrusters that burn hydrazine, and hydrazine and the tubing that feeds it must be kept above freezing. Push the power savings too far, and the fuel lines could chill to the point of freezing or fracturing.

This is why the engineers cannot simply turn everything off. They have to keep the spacecraft warm enough to protect its plumbing while cutting enough load to survive the year. It is a balance between two failure modes, running out of power and freezing the fuel, with a narrowing gap between them.

Why the thrusters matter so much

The thrusters are not for changing course. Voyager 1 is coasting outward and needs no push. Their job is to keep the spacecraft’s large dish antenna aimed back at Earth, correcting the slow drift in its orientation.

At this range that aim has to be near perfect. Voyager 1 is now more than 25 billion kilometres away, and its radio beam is narrow. A pointing error of only about half a degree would swing that beam away from Earth by roughly the distance between the Earth and the Sun, and the link would simply be gone. There is no one out there to nudge it back. If the thrusters that hold the antenna steady stop working, contact ends, and a spacecraft that can no longer be heard or commanded is effectively lost, whatever else still functions aboard it.

A fuel-line scare that was not hypothetical

The risk is not theoretical, as a genuine crisis in 2025 showed. Over 47 years, a fuel tube inside Voyager 1’s thrusters had been clogging with silicon dioxide, a residue shed by a rubber diaphragm in the fuel tank. The opening had narrowed from about a quarter of a millimetre to roughly 0.035 millimetres, around half the width of a human hair.

Voyager 1 had been relying on its backup roll thrusters since 2004, when its primary set was declared dead after losing power to two small internal heaters. By 2025 the backup thrusters were themselves showing signs of clogging. Facing the prospect of eventually losing the ability to point the antenna, engineers went back to the thrusters everyone had written off two decades earlier. They suspected the 2004 failure had not been mechanical at all, but a power switch left in the wrong position, and on 20 March 2025 a test firing of the long-idle primary roll thrusters succeeded. They had to finish before a major Deep Space Network antenna in Canberra went offline for upgrades from May 2025, since it is the one dish powerful enough to send commands to Voyager 1.

Talking to something this far away

Every one of these moves is made across a gulf that makes ordinary troubleshooting impossible. A command sent to Voyager 1 takes around 23 hours to arrive, and the reply takes just as long to come back, so a single exchange can eat up the better part of two days. The margin for error is small, the round trip is slow, and the spacecraft is running on hardware designed in the 1970s.

None of this buys unlimited time. Each instrument switched off returns a little power and postpones the next hard choice, but the generator keeps cooling and the list of things left to turn off keeps shrinking. The realistic hope is to keep at least one instrument reporting into the 2030s.

What the engineers are really managing is the order in which the spacecraft goes quiet. The aim is to make sure the last thing to fail is not the ability to talk, so that Voyager 1 keeps sending word from interstellar space until there is genuinely nothing left to send it with.