Voyager 1 is still talking to Earth on a radio transmitter that radiates roughly 22 watts — less than the bulb in most hallway fixtures — from more than 25 billion kilometres away, or over 170 times the distance between the Earth and the Sun. The reason a machine launched in 1977 still has electricity at all is a stack of three radioisotope thermoelectric generators packed with plutonium-238 dioxide, which produced about 470 watts between them at launch and have been shedding roughly four watts a year ever since. What reaches Earth is caught by 70-metre dishes on three continents and decoded at about 160 bits per second.
On Wednesday, 18 November 2026, at 2:16:07 a.m. Pacific time, NASA calculates that Voyager 1 will be 25,902,068,356 kilometres from Earth — one light-day, the first human-made object ever to reach that mark. Suzy Dodd, the mission’s project manager at the Jet Propulsion Laboratory, has described the practical consequence plainly: say good morning to Voyager 1 at eight o’clock on a Monday and the answer arrives at eight o’clock on Wednesday.
A 22-watt whisper and a 70-metre ear
The transmitter aboard Voyager 1 is not powerful. A modern kitchen microwave draws roughly 1,000 watts. A laptop charger pulls about 65. Voyager’s X-band radio radiates around 22 watts, the figure NASA itself uses when it compares the spacecraft’s output to a refrigerator light bulb or a ham radio set.
By the time that signal has spread across 25 billion kilometres, the inverse-square law has reduced it to something measured in attowatts — on the order of a billionth of a billionth of a watt arriving at the dish. It is not weak the way a distant station is weak. It is weak in a way that sits below the thermal noise of the receiving equipment itself, which is why the amplifiers are cryogenically cooled.
What makes this work is not brute force. It is geometry, patience, and an enormous ear on the ground. NASA’s Deep Space Network runs three complexes — Goldstone near Barstow in California, Robledo de Chavela outside Madrid, and Tidbinbilla near Canberra — spaced roughly 120 degrees apart so that a receding spacecraft is always in view of at least one of them. Each site has a 70-metre dish, about the width of a football pitch.
Those dishes integrate the signal over long stretches of time, pulling coherent bits out of the noise floor. The bit rate that emerges is glacial: around 160 bits per second, slower than a 1980s dial-up modem by orders of magnitude. Slow is not a defect here. A slower bit is a longer bit, and a longer bit carries more energy, which is exactly what makes it recoverable at the far end.
Commanding the spacecraft is harder than hearing it. Only one antenna on Earth — Deep Space Station 43, the 70-metre dish at Canberra — has enough transmitting power to send instructions to the Voyagers. When DSS-43 went down for a ten-month overhaul beginning 4 May 2025, the mission was reduced to brief command windows in August and December.
Communication also depends on aim. Voyager 1’s 3.7-metre high-gain antenna has to stay pointed at Earth to within a fraction of a degree, and the spacecraft uses small hydrazine thrusters to make the corrections. In March 2025, ahead of the antenna outage, JPL engineers revived a set of roll thrusters that had been written off as inoperable since 2004. If the heaters had failed to warm the fuel lines before the thrusters fired, the result could have been a small explosion aboard the most distant working machine humanity has built.
Plutonium pellets that were warm in 1977 and are still warm now
The power comes from a physics trick refined in the 1950s. Each of Voyager 1’s three radioisotope thermoelectric generators holds pressed pellets of plutonium-238 dioxide — a little over four kilograms of fuel per unit. The isotope has a half-life of about 87.7 years, which means a pellet cast before launch still holds roughly two-thirds of its original plutonium-238 today.
As the plutonium decays it emits alpha particles, and those particles heat the ceramic to hundreds of degrees Celsius. Thermocouples wrapped around the housing convert the temperature difference between the hot fuel and the cold of space directly into current. There are no moving parts. Nothing to seize. Nothing to lubricate. The RTG is essentially a hot brick that generates voltage for as long as the plutonium keeps decaying and the thermocouples keep functioning.
Both are failing, slowly, and for two separate reasons. The fuel decays at about 0.8 per cent a year, and the thermoelectric materials degrade at roughly the same rate. Together that works out to a loss of about four watts annually. The 470 watts available in 1977 is now somewhere in the low 200s, and every watt spent on one system is a watt unavailable to another.
Turning off the lights, one instrument at a time
To stretch what remains, engineers have been methodically switching things off. The cameras were powered down in 1990, shortly after Voyager 1 turned back toward the inner Solar System and captured the image known as the Pale Blue Dot — Earth as a fraction of a pixel, photographed on 14 February 1990 from 6.4 billion kilometres away.
Heaters went next, then the instruments themselves, one by one. The cosmic ray subsystem was shut down on 25 February 2025. On 17 April 2026, engineers at JPL sent commands to switch off the Low-energy Charged Particles experiment, which had been running almost without interruption since Cape Canaveral in September 1977. Seven of the ten original instruments are now dark.
Two remain: the magnetometer, which measures the strength and direction of the local magnetic field, and the plasma wave subsystem, which listens to the density oscillations of the interstellar medium. Kareem Badaruddin, the Voyager mission manager at JPL, said at the time that shutting down an instrument is nobody’s preference but was the best option available, and that both surviving instruments were still working well.
The plasma wave data is what confirmed, in 2012, that Voyager 1 had crossed the heliopause — the boundary where the Sun’s outward wind of charged particles gives way to the pressure of the galaxy itself. Voyager 2 crossed the same boundary in 2018. Both spacecraft are formally in interstellar space.
They are also, by the definition astronomers use, still deep inside the Solar System. The Oort Cloud — the shell of icy bodies bound to the Sun’s gravity — begins far beyond where either probe now sits.
The glitch that took five months to fix
The fragility of talking to a 46-year-old computer came into sharp relief on 14 November 2023, when Voyager 1 — then about 24 billion kilometres out — began sending back a repeating pattern of ones and zeros with no readable content inside it. The carrier signal was still there. The spacecraft was still receiving commands. The contents had simply stopped meaning anything.
In March 2024, engineers coaxed the spacecraft into returning a full readout of its memory, and the readout showed them the fault. Roughly three per cent of the flight data subsystem’s memory had been corrupted by a single failed chip — and that section happened to hold part of the software the computer runs. The FDS is one of three onboard computers, and its job is to package science and engineering data before transmission.
The chip could not be replaced. So the team rewrote the affected code, broke it into fragments, and found empty corners of memory elsewhere in the FDS where the pieces would fit and still function as a whole. The first relocated section went out on 18 April 2024. On 20 April, Voyager 1 returned readable engineering data for the first time in five months. Normal science operations resumed that June.
Every step in that diagnosis ran on a 45-hour clock. A command took about 22 and a half hours to arrive and the answer took the same again to come back. Send an instruction Monday. Wait until Wednesday morning. Analyse. Try again Thursday.
And the team was doing it against documentation written in the 1970s, on an architecture with a tiny fraction of the memory in a modern car key, using a Voyager-specific assembler that almost nobody alive learned as a first language. The engineers who designed the system have largely retired or died. There is no second attempt without a cost.
What one light-day actually means
Voyager 1 is receding from the Sun at approximately 17 kilometres per second — about 61,000 kilometres an hour, or 3.5 astronomical units a year. It is fast enough that a car setting off at highway speed on launch day in 1977 would still be tens of thousands of years short of catching it.
Put another way: at 50 mph, covering the distance Voyager 1 has already crossed would take roughly 36,000 years. At the cruising speed of a Boeing 777, about 3,200 years. Measured in round trips to the Moon and back, it is somewhere north of 33,000 of them, end to end.
Light does it in a day. At 299,792 kilometres per second, a photon covers about 25.9 billion kilometres in 24 hours — roughly 173 times the distance between the Earth and the Sun. When Voyager 1 crosses that line in November, a signal leaving Earth at the moment it passes would reach the spacecraft the following day, at the same clock time.
That is a distance humans have no intuition for. The Moon is 1.3 light-seconds away. The Sun is 8 minutes and 20 seconds. Neptune, at its farthest, is about four light-hours. Voyager 1 is about to be six times farther than that, and it took nearly half a century of continuous coasting to get there.
Human beings have never come close. As Gigazine notes, the speed record of 39,897 km/h set by Apollo 10 in 1969 still stands — and at that pace, crossing a single astronomical unit would take 155 days. Reaching where Voyager 1 sits now would take a crew more than seventy millennia.
Why it will keep going after it stops talking
Sometime in the early 2030s, according to the mission team, the remaining power will fall below the level needed to run even one instrument. The transmitter will go quiet. The spacecraft will keep coasting outward, toward the inner edge of the Oort Cloud, which NASA estimates it will reach in roughly 300 years. Crossing to the far side takes closer to 30,000.
Then the stars. NASA’s projections put Voyager 1 within about 1.7 light-years of AC +79 3888 — the red dwarf catalogued as Gliese 445, currently 17.6 light-years off — in roughly 40,000 years. Voyager 2 makes a comparable pass of Ross 248 in about the same span. Neither will be captured. Both will keep drifting, orbiting the centre of the Milky Way alongside everything else.
Bolted to the side of each spacecraft is a 12-inch gold-plated copper disc containing greetings in 55 languages, whale song, Chuck Berry’s “Johnny B. Goode,” and a map giving the Sun’s position relative to 14 pulsars. The records were etched to survive for a billion years in the interstellar medium — long after the Sun has swelled into a red giant and swallowed the inner planets.
The engineering brief in 1977 was to fly past Jupiter and Saturn and return data for four years. The mission is in its 49th year, and the team is aiming to reach the 50th anniversary in September 2027 with both spacecraft still answering. Voyager 1 has outlived most of the engineers who built it, several generations of the ground systems used to command it, and the tape-based data storage that produced it.
Right now, as you read this, a 22-watt signal that left the spacecraft yesterday is arriving at a dish in the Mojave Desert, or outside Madrid, or in a valley southwest of Canberra. It carries a few hundred bits about the magnetic field in a place nothing else has ever been. In a few years it will stop, and the antenna will go on pointing at Earth anyway, for as long as the aluminium holds.
