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In spring 2025, NASA engineers brought back to life a set of thrusters that had been considered dead for 21 years. None of the engineers could get closer than 25 billion kilometers (15.5 billion miles) to them. The command took almost a day to arrive, and the answer took almost as long to come back. The machine is Voyager 1. It is 49 years old, and people are still repairing it.
On November 18, 2026, Voyager 1 will be 25.9 billion kilometers (16.1 billion miles) from Earth. That is one light-day: a radio signal from our antennas will need a full 24 hours to reach it. No human-made object has ever been this far away, as NASA points out . A simple “do you read me?” takes a day to arrive, and the answer takes another day to come back.
A day per phone call
A light-day measures distance, not time. It is how far light travels in 24 hours: 25,902,068,356 km. Light reaches the Moon in 1.3 seconds; the Artemis II crew took about three days.
// How long a signal travels
Voyager 1’s twin, Voyager 2, is on a different path and will not reach the one-light-day mark until November 2035.
A refrigerator light bulb
Voyager 1’s transmitter puts out about 23 watts. JPL, the NASA lab that runs the mission, once compared it to the bulb inside a fridge. By the time that glow reaches Earth, it has faded to less than a billionth of a billionth of a watt. In 2013, instrument data came down at about 160 bits per second. At that speed, a single smartphone photo would take more than a day to download.
That is why only the giant dishes of NASA’s Deep Space Network can hear a whisper that faint. And only one antenna in the entire network can talk back: DSS-43, a 70-meter dish near Canberra, Australia. It was offline for upgrades from May 2025 to February 2026, and during that time the team could reach the probes only in short windows in August and December, when the dish briefly came back into service.
Fixing it blind, 45 hours per round trip
On November 14, 2023, Voyager 1 stopped making sense. It still obeyed commands, but instead of reports on itself and its surroundings it sent back an unreadable stream of bits. In early March 2024, engineers sent it a “poke” command: a request to read out the memory of one of its three onboard computers, the one that packages data before transmission. That readout revealed the cause . About 3% of the memory was corrupted, most likely because a single chip had failed, taking part of the software with it. Nobody knows exactly why. Maybe an energetic particle from space hit the chip. Maybe it simply wore out after 46 years.
You cannot swap a chip that far out, and no free block of memory was big enough to hold the lost code in one piece. So the team cut the code into sections and tucked them into different corners of the memory. Picture a book with a chapter torn out and no run of blank pages left: you reprint the chapter in pieces on whatever pages are free, then fix every “see page N” in the book so the reader doesn’t get lost. The first batch went up on April 18, 2024. With 22.5 hours each way, the reply arrived on April 20: the first readable health report in five months. In May, the probe started sending science data again.
A transmitter silent since 1981
In October 2024, engineers asked Voyager 1 to turn on one of its heaters. There should have been enough power, but the fault protection system kicked in. When the probe draws too much power, this system shuts off anything nonessential. First it lowered the data rate, then it switched off the main transmitter and fell back to a backup one. Voyager 1 had not used that backup to talk to Earth since 1981, and its signal is much fainter. The team was not sure it could be heard at that distance at all. The antennas picked it up anyway, and by late November the probe was back to normal operations.
Thrusters that were dead for 21 years
Voyager’s antenna has to stay pointed at Earth, so the probe locks onto a guide star and nudges itself with small thrusters. Voyager 1’s primary roll thrusters quit in 2004, when two tiny heaters they need lost power. The fault was judged unfixable, and the team moved to the backup set. As mission manager Kareem Badaruddin put it, back then people probably didn’t think the Voyagers would keep going for another 20 years. Todd Barber, the mission’s propulsion lead, remembers it this way:
These thrusters were considered dead. And that was a legitimate conclusion.
By 2025, residue from the propellant was building up in the backup thrusters’ fuel tubes, and they could clog as early as that fall. The engineers suspected the old heaters had never actually broken. A glitch in the power circuit might simply have flipped a switch to the wrong position. Testing that idea was risky. If the probe drifted too far from its guide star during the test, the thrusters would fire on their own, and firing them with cold heaters could cause a small explosion.
The commands went up on March 20, 2025 . They spent more than 23 hours traveling to the probe. Then the data about what happened spent more than 23 hours traveling back. Once it arrived, the first 20 minutes showed the heater temperatures shooting up. It had worked. The engineers were celebrating something that had happened out there nearly a day earlier. “It was such a glorious moment,” Barber said. The timing was tight. Six weeks later, DSS-43, the only antenna that can send Voyager commands, went offline for its upgrade.
Four watts a year
Power on board comes from radioisotope generators, which turn the heat of decaying plutonium into electricity. Each probe loses about 4 watts a year, roughly a sixth of what that 23-watt “fridge bulb” transmitter puts out, so the team switches off instruments one by one, following a list agreed on years ago.
The cameras went first. On February 14, 1990, Voyager 1 took a “family portrait” of the solar system, and in one frame Earth took up about a single pixel. That is the famous Pale Blue Dot. Thirty-four minutes later, the cameras were turned off for good to save power for the long road ahead.
On April 17, 2026, the team shut down an instrument on Voyager 1 that caught charged particles and had run almost nonstop since launch in 1977.
Out of ten science instruments, the probe now has two left running : the magnetometer and the plasma wave sensor.
Project manager Suzanne Dodd was blunt about it in 2025: without the shutdowns, the probes would probably have only a few more months of power. With the savings, they might keep at least one instrument going into the 2030s. After half a century in deep space, nobody is promising anything.
A question about yesterday
Voyager 1 is moving at nearly 61,000 km/h (38,000 mph) toward the star Gliese 445. In about 40,000 years it will pass within 1.7 light-years of it. Its generators will have gone cold long before then.
Ed Stone led Voyager’s science for half a century and died in 2024. He said that with the Voyagers, every day is a day of discovery. From November 18, each of those days will reach Earth a full day late. The team will learn about any new fault at least a day after it happens, and the fix will need another day to get there. One question and one answer will take two days. That is what every repair will look like from now on.
