Communications with NASA's Voyager 1, which is traveling through interstellar space about 25.8 billion kilometers from Earth, were lost between October 18 and 19, 2026. NASA's Deep Space Network (DSN) failed to receive a signal from the probe during two routine contacts held 24 hours apart. At this distance, a command from Earth takes about 24 hours to arrive, so engineers cannot respond immediately when something goes wrong. On October 20, however, before the ground team could send a recovery command, the probe's signal was detected again, restoring communications after roughly 48 hours.
The incident followed a large-scale power-saving operation that NASA's mission team completed in early September, which it called the "Big Bang." About 49 years after its 1977 launch, Voyager 1 has less and less power available because the output of its nuclear power source keeps falling. Nor can engineers simply switch equipment off: in the extreme cold of space, instruments must be kept at appropriate temperatures to keep working.
NASA's operations report, published October 29, 2026, describes both the September power-saving work and the October communications blackout. Communications have been restored, but the cause of the automatic thruster switchover remains under investigation. Meanwhile, on November 18, Voyager 1 is expected to become the first human-made object to reach a distance of one light-day from Earth. The milestone underscores a basic difficulty of deep space exploration: it takes a full two days to send a command and confirm the response.
Balancing power and temperature: the September instrument swap
Voyager 1 and its twin, Voyager 2, fly far from the Sun in interstellar space, where sunlight cannot supply enough power. Both probes run on radioisotope thermoelectric generators (RTGs), which convert heat from the radioactive decay of plutonium-238 into electricity. Because the heat output from plutonium-238 decay is declining and the thermoelectric converters are aging, the available power falls by about 4 watts every year. Nearly half a century after launch, the power margin is extremely thin.
The operations team has so far saved power by gradually turning off science instrument heaters and other nonessential equipment. But the heat given off by onboard electronics also helps keep the spacecraft warm, so shutting equipment down risks overcooling some devices and structures. Electronics, propulsion lines, fuel tanks and other components must be kept at suitable temperatures, which makes power management and thermal design inseparable.
To address this, the team carried out the "Big Bang" instrument swap in early September 2026. It turned off three units that had been in use and switched to three lower-power replacements. Notably, all three swaps had to be done at the same time. The six units involved also contribute to the probe's temperature control, and switching them one at a time might have disrupted the spacecraft's heat distribution. Doing all three at once cut power consumption without compromising thermal management.
The same work had been done on Voyager 2 about six weeks earlier, and NASA announced the results on August 4. For Voyager 2, the team expects to be able to keep three science instruments running together for at least one more year. For Voyager 1, NASA has not published the extension period or the amount of power saved, but without this work the team would have had to turn off another instrument as early as summer 2027.
The work did not restore the RTGs' generating capacity, and available power will keep declining. What the team did was rethink how power is used while keeping the probe's internal temperatures appropriate, extending the period in which science observations can continue. Postponing an instrument shutdown is a significant achievement, but it does not avoid future shutdowns.
About 48 hours of silence, and an automatic switch to backup thrusters
About a month and a half after the power-saving work, communications with Voyager 1 were disrupted on October 18 and 19, 2026. The DSN maintains contact with distant spacecraft through three ground facilities: Goldstone in California, Madrid in Spain, and Canberra in Australia. Each site has large antennas, including 70-meter dishes, but in two routine contacts 24 hours apart, none of them detected a signal from Voyager 1.
Then, on October 20, the probe's signal was detected again before any recovery command was sent from the ground. After communications resumed, the operations team examined the telemetry and found that the thrusters normally in use had stopped and a backup set was active. Thrusters expel propellant to control the spacecraft's attitude, and are also used to keep its high-gain antenna pointed at Earth. According to NASA, the system is designed to switch automatically to a backup set when a problem is detected with the thrusters in use.
The switch was carried out by an onboard safety function called fault protection. At a distance where a signal takes about a day to reach Earth, ground engineers cannot deal with an equipment problem in real time. The probe's computer is therefore designed, when it detects a fault, to pause normal operations as needed and move to a safe, stable state. That reduces the risk of a critical situation developing while the ground team investigates the cause.
However, it is not known whether the thruster switchover caused the communications blackout or occurred alongside some other fault. NASA has not identified whether the antenna's pointing briefly drifted or whether a problem arose in the communications system. The automatic thruster switch and the restoration of contact without ground intervention are both confirmed, but the two are not necessarily directly related.
Voyager 1 also experienced a fault-protection communications problem in October 2024. In that case, the X-band transmitter normally in use shut off and the probe automatically switched to the lower-power S-band transmitter. The latest event involved a switch of thruster sets rather than transmitters, and there is no evidence that the two share a common cause. They need to be investigated as separate events on an aging spacecraft.
| Event | What NASA has confirmed or projected | Unresolved points or caveats | Operational significance |
|---|---|---|---|
| September 2026 "Big Bang" | Three units were turned off and replaced simultaneously with three lower-power units | Power saved on Voyager 1 and the specific extension period have not been published | Saves power while maintaining heat distribution, postponing an instrument shutdown |
| October 2026 communications blackout | Communications resumed after about 48 hours without a ground recovery command; automatic switch to backup thrusters confirmed | The root cause of the switch and its relationship to the blackout are under investigation | Confirms the autonomous safety function worked, but shows operational risks from aging |
| November 2026 arrival at one light-day | On November 18, about 25.9 billion km from Earth, with one-way radio travel time reaching 24 hours | Not a physical boundary crossing; no change in surroundings is expected | Round-trip communications delay reaches about 48 hours, lengthening responses to anomalies |
One light-day from Earth: 48 hours for a round trip
Voyager 1 is moving outward from the solar system at about 17 kilometers per second (about 61,155 km/h). According to NASA's projection, it will reach a distance of one light-day from Earth at 5:16:07 a.m. U.S. Eastern Time on November 18, 2026. A light-day is the distance light travels in a vacuum in 24 hours: 16,094,799,096 miles, or about 25,902,068,356 kilometers (roughly 25.9 billion km).
Reaching one light-day does not mean crossing an astrophysical boundary, though. Voyager 1 passed through the heliopause, the edge of the heliosphere, in 2012 and entered interstellar space. At the heliopause, the physical environment changes through the interaction of the solar wind and interstellar matter, but a light-day is merely a measure of distance from Earth. NASA also explains that passing this point will not change the probe's surroundings or its internal condition.
From a communications standpoint, however, the distance matters. Radio waves travel at the speed of light, so a command sent from Earth takes 24 hours to reach Voyager 1, and even if the probe responds immediately, its signal takes another 24 hours to return. That means the round-trip light time (RTLT) from sending a command to confirming its result will be about 48 hours at minimum.
This delay is a major constraint when investigating an anomaly. Telemetry received on the ground shows the probe's state as it was about 24 hours earlier, and even if engineers send a corrective command, they can confirm the result no sooner than 48 hours later. In practice, preparing commands and processing them onboard take additional time, so going from detecting a fault to recovery takes even longer. The October blackout again showed how important autonomous safety functions are in deep space, where the ground cannot intervene right away.
Two instruments remain: how long can direct interstellar observation continue?
Voyager 1 and Voyager 2 have left the heliosphere, the vast region shaped by the solar wind, and are observing interstellar space directly. Both probes were launched in 1977 carrying 10 science instruments each, originally to study the outer planets such as Jupiter and Saturn and their moons. After their planetary flybys, instruments such as the cameras were gradually turned off as they were no longer needed, but observations of magnetic fields, charged particles and plasma have continued, collecting important data on the boundary between the heliosphere and interstellar space.
As power declines, however, fewer instruments can operate. According to the instrument status published by NASA, only two instruments are currently operating on Voyager 1: the magnetometer (MAG) and the Plasma Wave Subsystem (PWS). The magnetometer measures the magnetic field in interstellar space, while the Plasma Wave Subsystem observes wave phenomena in the plasma, providing data useful for estimating its properties and density. The Cosmic Ray Subsystem (CRS) was turned off on February 25, 2025, and the Low-Energy Charged Particle instrument (LECP) on April 17, 2026, both to save power.
Data from the remaining two instruments are important for studying the structure of the interstellar magnetic field and how disturbances caused by solar activity propagate into interstellar space. Satellites and telescopes near Earth cannot directly measure the magnetic field and plasma where Voyager 1 is flying. Keeping even one instrument running longer therefore preserves the ability to collect science data that has no substitute.
データを表で見る
| Science instruments (instruments) | |
|---|---|
| 1977 at launch | 10 |
| 2026 currently operating | 2 |
NASA expects the instrument swap to extend the observation period, but it has not offered any new specific projection of how many years the mission can continue. The probe's future lifespan depends not only on the decline in RTG output but also on instrument degradation and unexpected failures. The cause of the communications blackout has not been identified, and clarifying the relationship between the automatic thruster switch and the communications anomaly will be a challenge for stable operations going forward.
After about 49 years, Voyager 1 continues to operate far beyond what its designers expected. Reaching one light-day from Earth symbolizes the length of its journey, while also highlighting the unavoidable constraints of communications delay and power shortage. How to allocate the remaining power and how to protect aging equipment are the open questions. How long data from interstellar space can keep arriving depends on finding the cause of this communications anomaly and on future power management.