The Long Goodbye: NASA Powers Down Another Voyager 1 Instrument as Humanity's Farthest Spacecraft Fades

On April 17, 2026, engineers at NASA's Jet Propulsion Laboratory in Pasadena, California, sent a sequence of commands across 15 billion miles of space. The signal, traveling at the speed of light, took more than 22 hours to reach Voyager 1 — and another 22 hours for confirmation to come back. The instruction was simple and irreversible: shut down the Low-Energy Charged Particles experiment, an instrument that had been running nearly without interruption since September 5, 1977 [1].

With that command, Voyager 1 — the most distant human-made object in existence — dropped to just two functioning science instruments out of the ten it carried at launch. The spacecraft is not dying, exactly. But it is going dark, one system at a time, as the plutonium that powers it slowly decays into silence.

The Physics of a Slow Death

Voyager 1 runs on three radioisotope thermoelectric generators (RTGs), devices that convert heat from the natural decay of plutonium-238 into electricity. At launch in 1977, these generators produced approximately 470 watts of electrical power — enough to light a handful of household bulbs [2]. The physics of radioactive decay are unforgiving: plutonium-238 has a half-life of 87.7 years, meaning the fuel loses about 0.8% of its thermal output annually [3]. On top of that, the silicon-germanium thermocouples that convert heat to electricity degrade over time, compounding the loss.

Source: NASA/JPL

Data as of Apr 17, 2026CSV

Today, Voyager 1's RTGs produce roughly 249 watts [4]. The spacecraft's essential systems — heaters, computers, communications equipment — consume a fixed baseline of power. What remains for science instruments is a shrinking margin that engineers have managed with increasing creativity for decades. Both Voyager probes lose about 4 watts of electrical power per year [1].

The immediate trigger for the April shutdown was an unexpected power drop during a routine roll maneuver in late February 2026. The maneuver, which orients the spacecraft's antenna toward Earth, consumed more power than expected, forcing the team to act faster than planned [5].

What Was Lost

The Low-Energy Charged Particles experiment, or LECP, was built by the Johns Hopkins University Applied Physics Laboratory. It measured the energy, composition, and angular distribution of low-energy ions (above 30 keV) and electrons (above 20 keV) streaming through interstellar space [6]. In practical terms, LECP was one of the instruments that told us what interstellar space actually feels like at the particle level.

The LECP made landmark contributions to heliophysics. In December 2004, it detected the termination shock — the boundary where the solar wind slows from supersonic to subsonic speeds as it collides with the interstellar medium [6]. It was also one of two instruments that confirmed Voyager 1's crossing of the heliopause in August 2012, registering the dramatic transition from solar-origin particles to galactic cosmic rays [1]. That crossing was the moment Voyager 1 became the first human-made object to enter interstellar space.

No other spacecraft can replicate these measurements. Voyager 2 shut down its own LECP in March 2025 [7]. No current or planned mission is positioned in interstellar space. The data stream from LECP was, until April 17, unique in the history of science.

Two Instruments Remain

Voyager 1 now operates with only its Magnetometer (MAG) and Plasma Wave Subsystem (PWS) [1]. The magnetometer measures the strength and direction of magnetic fields in the interstellar medium. The plasma wave instrument detects density changes in interstellar plasma by "listening" for oscillations in the electron density of the medium surrounding the spacecraft [8].

Together, these two instruments continue to address fundamental questions. The interstellar magnetic field's structure remains poorly understood — is it smooth and uniform, or turbulent and tangled? The PWS has already revealed a large-scale density gradient and turbulence outside the heliopause, findings published in Nature Astronomy in 2021 [8]. The magnetometer, meanwhile, tracks how the Sun's magnetic influence fades with distance, mapping the transition zone between solar and galactic magnetic domains.

Source: NASA/JPL

Data as of Apr 17, 2026CSV

Given the current power supply, NASA expects Voyager 1 can operate in this two-instrument configuration for about a year [9]. After that, without intervention, one of the final two instruments will have to go.

The "Big Bang" Gamble

The Voyager team is not waiting passively. Engineers have developed an ambitious power conservation plan they informally call "the Big Bang" — a coordinated swap of several powered subsystems all at once, replacing older components with lower-power alternatives [5]. The idea is to free up enough wattage to keep at least one science instrument running well into the 2030s.

The plan carries real risk. At Voyager 1's distance, every command takes nearly two days for a round trip. If something goes wrong during a complex multi-system swap, the team has limited ability to diagnose and respond. A wrong step could leave the spacecraft in an unrecoverable state.

The team will test the Big Bang on Voyager 2 first — it has slightly more power to spare and is closer to Earth (about 12.8 billion miles away). Tests are planned for May and June 2026. If they succeed, the same procedure will be attempted on Voyager 1 no sooner than July 2026 [1]. If it works, there is a chance that the LECP could be switched back on [5].

A Half-Century of Shutdowns

The April 2026 shutdown was not the first, or even the fifth, time Voyager 1 has lost an instrument. Of the ten science instruments the spacecraft carried at launch, eight have now been turned off [1].

Several instruments were shut down after the planetary encounter phase ended. The imaging system, infrared spectrometer, photopolarimeter, and ultraviolet spectrometer were deactivated after the Saturn flyby in 1980, as there were no more planetary targets to photograph [2]. The plasma science instrument was turned off years ago due to degraded performance [10]. The cosmic ray subsystem — a suite of three telescopes designed to study galactic and solar protons — was shut down on February 25, 2025 [7].

When the Voyager missions were designed in the early 1970s, their primary objective was a "Grand Tour" of the outer planets, taking advantage of a rare alignment of Jupiter, Saturn, Uranus, and Neptune that occurs once every 176 years. The nominal mission was four years. That Voyager 1 is still returning science data after nearly 49 years represents one of the most extreme cases of mission overperformance in the history of spaceflight [11]. The original engineers could not have predicted their spacecraft would still be functioning — let alone doing science — in the interstellar medium.

The Budget Question

The Voyager Interstellar Mission costs approximately $4.2 to $5 million per year to operate, covering Deep Space Network tracking time, a small team of engineers and scientists at JPL, and data processing [12]. In context, this is a rounding error in NASA's $24.4 billion annual budget [13].

For comparison, the James Webb Space Telescope's operational phase is budgeted at roughly $172 million per year [14]. The Juno mission to Jupiter has cost approximately $1.1 billion over its lifetime [12]. By any measure, Voyager offers an extraordinary ratio of scientific return to cost — ongoing measurements from interstellar space for less than the price of a modest building renovation.

Yet even this modest budget faces pressure. In October 2025, reports emerged that the Voyager program was facing a 26% budget cut as part of broader reductions at JPL [15]. The Trump administration's FY 2027 budget proposal would cut NASA's Science Mission Directorate from $7.25 billion to $3.9 billion — a 47% reduction that the Planetary Society called the largest single-year cut to science funding in the agency's history [16]. Nearly 300 current and former NASA employees signed the "Voyager Declaration," a letter rebuking the proposed cuts [16].

The counterargument — that funding a 49-year-old probe crowds out newer missions — has limited force when the annual cost is $5 million. That amount would fund roughly 11 hours of JWST operations. The science Voyager returns is irreplaceable: no other instrument platform exists in interstellar space, and none will for decades.

RTGs Across the Fleet

All deep-space missions beyond Mars rely on RTGs, and all face the same plutonium decay curve. The physics is identical — plutonium-238's half-life does not vary — but engineering choices made decades ago have shaped each mission's power trajectory differently [3].

Voyager's MHW-RTGs (Multi-Hundred Watt RTGs) each contained about 4.5 kg of plutonium-238 and initially produced about 157 watts per unit. Three units gave the spacecraft its 470-watt starting budget [3]. New Horizons, launched in 2006 with a single GPHS-RTG (General Purpose Heat Source RTG), started with 245.7 watts and loses approximately 3.5 watts per year [3]. Cassini, the Saturn orbiter that operated from 1997 to 2017, carried three GPHS-RTGs producing a combined 870 watts from 33 kg of plutonium-238 oxide [17].

The key 1970s engineering decision that now looks prescient was redundancy. By including three RTGs rather than a smaller number, the Voyager designers gave the spacecraft a power margin that has allowed nearly five decades of operation — far beyond any reasonable expectation. What looks limiting in hindsight is the thermocouple technology: modern RTGs achieve higher conversion efficiencies, meaning a 2020s-era spacecraft could extract more electricity from the same amount of plutonium.

The Successor That Never Launched

Scientists have proposed follow-on interstellar missions for decades. None has been funded.

The most developed concept is the Interstellar Probe study, led by the Johns Hopkins Applied Physics Laboratory. The proposal envisions a spacecraft that would use a close solar flyby (a solar Oberth maneuver) to achieve speeds far exceeding Voyager's 38,000 mph, reaching 1,000 astronomical units from the Sun within 50 years [18]. If approved and launched around 2036, it could reach Voyager 1's current distance in substantially less time than the 47 years Voyager required.

The estimated cost — around $1.5 billion, comparable to the Parker Solar Probe — is not astronomical by NASA flagship mission standards [18]. But the mission's multi-generational timeline is a hard sell in a funding environment driven by congressional budget cycles and near-term deliverables. A 50- to 100-year mission would span the careers of multiple generations of scientists.

China has proposed its own concept, "Interstellar Express," with two probes — one targeted for launch as early as possible and another around 2030 — aimed at reaching the outer heliosphere by 2049 [19]. Whether these proposals advance depends on sustained political commitment that neither the United States nor China has yet demonstrated for interstellar exploration.

In 2025, NASA launched the Interstellar Mapping and Acceleration Probe (IMAP), which studies the solar wind and heliosphere from a vantage point near Earth [18]. IMAP is valuable but fundamentally different from an interstellar probe: it observes the heliosphere's boundary remotely rather than passing through it.

The Last Keepers

The question of institutional knowledge is acute. Edward Stone, who served as Voyager's project scientist for 50 years — from the mission's inception in 1972 through his retirement in 2022 — died on June 9, 2024, at age 88 [20]. Stone was the public face of Voyager and the person who understood its scientific arc better than anyone alive. His death severed a direct link to the mission's origins.

Linda Spilker succeeded Stone as project scientist. Spilker was a member of the original Voyager science team during the Jupiter, Saturn, Uranus, and Neptune flybys, later led the Cassini mission, and returned to Voyager as deputy project scientist in 2021 [21]. Suzanne Dodd, the project manager, started her career on Voyager and has said she will likely end it there [22].

But the team is small — fewer than a dozen people manage the day-to-day operations of both spacecraft — and the institutional knowledge required to interpret Voyager data, diagnose anomalies in 1970s-era hardware, and send commands across 15 billion miles of space is not easily transferable. As the mission approaches its end, the window for training successors narrows. The spacecraft's custom-built flight computers use an architecture that predates the IBM PC by four years. Documentation exists, but the practical intuition of operators who have worked with these systems for decades cannot be fully captured in manuals.

What Science Remains

Source: OpenAlex

Data as of Jan 1, 2026CSV

Even with just two instruments, Voyager 1 continues to answer questions that no other mission can address. The interstellar medium — the space between stars — remains poorly characterized. Key unresolved phenomena include:

Interstellar magnetic field structure. The magnetometer is mapping how galactic magnetic fields behave at scales never before measured in situ. Whether the local interstellar magnetic field is ordered or chaotic at various scales has implications for models of galactic structure and cosmic ray propagation [8].

Plasma density variations. The PWS has revealed unexpected density fluctuations in the interstellar plasma, suggesting turbulence driven by sources not yet identified. Understanding these variations matters for models of how the heliosphere interacts with its galactic environment [8].

The heliosphere's shape. Data from both Voyagers — Voyager 1 exited the heliosphere at the "nose" facing into the interstellar wind, while Voyager 2 exited at a different angle — suggest the heliosphere may not be the symmetric bubble depicted in textbooks. The surviving instruments continue to refine this picture [11].

Cosmic ray flux at distance. While the cosmic ray subsystem has been shut down, the remaining instruments provide indirect measurements of the cosmic ray environment through its effects on plasma and magnetic field conditions [6].

These questions will go unanswered once Voyager falls silent. The nearest interstellar probe, if approved today, would not reach comparable distances until the 2080s at the earliest.

The Clock Runs Down

The Voyager team has planned for this moment for years. The order of instrument shutdowns was agreed upon long ago by the science and engineering teams, balancing scientific priority against power requirements [1]. The magnetometer and plasma wave instrument were kept for last because they consume relatively little power and address the highest-priority interstellar science questions.

If the Big Bang maneuver succeeds, Voyager 1 could operate with at least one science instrument into the 2030s [1]. Even after the last instrument goes dark, the spacecraft will continue to transmit engineering data — temperature readings, power levels, system status — for some years after that. NASA estimates the spacecraft could maintain communication until approximately 2036 [2].

After that, Voyager 1 will continue its outward journey in silence, carrying the Golden Record — a phonograph disc containing sounds and images from Earth — into the galaxy at 38,000 miles per hour. It will pass near no star for roughly 40,000 years, when it will drift within 1.6 light-years of Gliese 445 in the constellation Camelopardalis [2].

For now, two instruments keep listening. The data they send back — arriving as a whisper of 160 bits per second across 15 billion miles — remains unlike anything else in science: direct measurements from a place no human technology has reached before, and none will reach again for a very long time.