On 5 September 1977, a Titan IIIE rocket lifted off from Cape Canaveral carrying an 815-kilogram spacecraft roughly the size of a small car. Its mission, as originally scoped, was a four-year tour of Jupiter and Saturn. Forty-eight years later, Voyager 1 is roughly 25.5 billion kilometres from Earth, moving at about 17 kilometres per second, and it is still talking to Earth.
According to NASA’s live mission status page, a radio command sent from the Deep Space Network today takes about 23 and a half hours to arrive — and another 23 and a half hours for the reply to come back. On 18 November 2026, Voyager 1 will officially cross the one-light-day threshold from Earth, the first human-made object ever to reach that distance.
The astonishing part isn’t the distance. It is that the spacecraft is doing this on less power than it takes to run a desk lamp.
A nuclear battery, slowly running down
Voyager 1 doesn’t use solar panels. Beyond Jupiter, sunlight is too weak to be useful, so the spacecraft carries three Multi-Hundred Watt Radioisotope Thermoelectric Generators (MHW-RTGs), each loaded with plutonium-238 dioxide. As the plutonium decays, it produces heat; thermocouples convert a fraction of that heat into electricity. There are no moving parts, nothing to break — just physics slowly winding down.
At launch, the three RTGs produced a combined 470 watts. Plutonium-238 has a half-life of about 87.7 years, so the fuel itself decays predictably, but the thermocouples degrade faster than the fuel does. By early 2026, the total power output had dropped to roughly 220 watts, and it continues to fall by about 4 watts every year. NASA engineers have spent decades shutting off instruments one by one to stay inside the shrinking energy envelope. The cameras were powered down in 1990 after the famous “Pale Blue Dot” image. The plasma science instrument stopped working in 1980 and was formally switched off in 2007. More recently, the cosmic ray subsystem was turned off in February 2025, and the Low-Energy Charged Particles experiment followed in April 2026. Of the ten instruments Voyager 1 carried at launch, only two are still switched on.
The signal that reaches Earth
Voyager 1’s radio transmitter runs at about 22 watts — comparable to a refrigerator lightbulb. By the time that signal reaches Earth, it has spread out over 25 billion kilometres of space. The power arriving at the Deep Space Network’s 70-metre dishes in California, Spain and Australia is on the order of 10⁻¹⁸ watts. That is roughly a billion times weaker than the signal from a modern GPS satellite, and about twenty billion times weaker than the noise floor of an ordinary FM radio.
Pulling that whisper out of the cosmic background requires cryogenically cooled receivers, careful timing, and — critically — knowing exactly where in the sky to point. The X-band downlink runs at just 160 bits per second for engineering data, slower than a 1980s dial-up modem by a factor of hundreds. Sending a full science frame home can take hours.
The 2023 glitch
In November 2023, Voyager 1 began transmitting a repeating pattern of ones and zeros instead of readable telemetry. For five months, the spacecraft was still alive — the carrier signal was fine — but nothing it said made sense. Engineers at the Jet Propulsion Laboratory eventually traced the fault to a single failed chip in the Flight Data System, one of three onboard computers built in the 1970s using technology that predates the microprocessor as most people know it.
The fix, described in an April 2024 JPL update, was to rewrite the affected software so that the corrupted memory was no longer used, then split the code across other regions of memory and patch every reference. The team had to dig out decades-old documentation — some of it on paper — from engineers who had long since retired. The first relocated code was uploaded on 18 April 2024. It took about 22 and a half hours to reach the spacecraft, and 22 and a half hours after that, on 20 April, a coherent reply came back. Voyager 1 was speaking again.
Where it is, and what it is doing there
In August 2012, Voyager 1 crossed the heliopause, the boundary where the Sun’s outward-streaming solar wind gives way to the interstellar medium. It became the first human-made object to enter interstellar space, though it is still technically inside the Solar System — the gravitational sphere of the Sun extends far beyond the heliopause, out to the distant Oort Cloud.
The two instruments still operating — the magnetometer and the plasma wave subsystem — measure magnetic fields and plasma waves in a region no probe has ever sampled before. The data trickles back at 160 bits per second and is genuinely new science: readings from a place no theory has ever been tested against directly. In May 2021, a Cornell-led team reported in Nature Astronomy that Voyager 1’s plasma wave subsystem had picked up a persistent, faint hum — a continuous vibration of the interstellar medium itself — that had no counterpart in any modelled environment.
The clock on the mission
Every watt lost is a decision. NASA has already worked through most of the schedule. After the cosmic ray subsystem was shut off in February 2025 and the Low-Energy Charged Particles experiment in April 2026, only the magnetometer and the plasma wave subsystem remain switched on. Both are expected to be turned off at some point in the coming years to keep the transmitter and the heaters alive. After that, Voyager 1 will continue to send engineering data — essentially telling Earth that it is still there — until, sometime in the 2030s, there simply will not be enough power to run the radio at all.
When that happens, the spacecraft will not stop. It will keep moving at 17 kilometres per second, carrying its Golden Record — a gold-plated copper phonograph disc containing greetings in 55 languages, music from Bach to Chuck Berry, and images of Earth — into the galaxy. In roughly 40,000 years, Voyager 1 will pass within about 1.6 light-years of a star called Gliese 445, in the constellation Camelopardalis. Nobody will be listening from Earth by then. The record is a message with no expected recipient and no expected reader.
Why it still matters
Voyager 1 is, in a strict engineering sense, a 1970s computer with a nuclear battery and a 3.7-metre dish antenna, held together by software patches and institutional memory. It is also the farthest, longest-operating spacecraft in history, and the first physical object built by humans to leave the bubble of the Sun’s influence. Every day it continues to function is a day past the wildest projections of the engineers who built it — many of whom, like Voyager’s longtime project scientist Ed Stone, who died in June 2024 at the age of 88, did not live to see the mission end.
When the last signal fades — and it will, probably sometime in the next decade — there will be no successor already in flight. No other spacecraft is on a trajectory to leave the Solar System with working instruments. Voyager 1 and its twin Voyager 2 are, for now, the only human hardware in interstellar space. The whisper coming in at 10⁻¹⁸ watts, decoded almost a full day late, is the sound of something that was never supposed to still be there.
For a similar story about how much can hang on a single component of ancient hardware, see the account of how in September 1947 engineers at Harvard pulled a moth from a relay inside the Mark II computer and coined a term that outlived the machine by decades.
