Voyager 1 Powers Down Another Instrument as NASA Engineers Race Against Plutonium Decay

On April 17, 2026, engineers at NASA's Jet Propulsion Laboratory in Southern California sent a command to Voyager 1 — humanity's most distant spacecraft, now over 15.5 billion miles from Earth. Twenty-three hours later, the signal arrived. The spacecraft's Low-Energy Charged Particle (LECP) instrument, which had been measuring ions and electrons in interstellar space since 1977, went dark [1].

The shutdown leaves Voyager 1 with two operating science instruments: a magnetometer and a plasma wave detector. When the probe launched nearly half a century ago, it carried eleven [2].

"While shutting down a science instrument is not anybody's preference, it is the best option available," said Kareem Badaruddin, Voyager mission manager at JPL [1].

The Physics of an Irreversible Decline

Voyager 1's power comes from three radioisotope thermoelectric generators (RTGs), which convert heat from the decay of plutonium-238 into electricity. At launch in 1977, the RTGs produced about 470 watts [3]. Today, that figure has fallen to roughly 210 watts — a loss of about 4 watts per year, driven by the 87.7-year half-life of the plutonium fuel and gradual degradation of the silicon-germanium thermocouples that convert heat to current [3][4].

Source: NASA/JPL Voyager Mission Data

Data as of Apr 17, 2026CSV

The power decline is governed by physics, not engineering failure. No software patch or hardware fix can reverse it. Each watt lost forces the mission team into triage: which systems stay on, and which go silent forever?

The LECP instrument consumed a modest amount of power, but every fraction of a watt matters at these margins. Its motor alone drew 0.5 watts. JPL estimates the shutdown buys approximately one additional year of operating time for the remaining instruments [1].

Without the shutdown, the spacecraft risked triggering its undervoltage fault protection system — an automated safety mode that could shut down multiple systems simultaneously. Recovering from such an event at interstellar distances, where a round-trip signal takes nearly two days, would carry significant risk [1].

A Cascading Timeline of Shutdowns

The LECP deactivation is the latest in a long sequence of instrument shutdowns stretching back to the 1980s, when NASA switched off several instruments after Voyager 1 completed its study of Jupiter and Saturn [5].

Source: NASA/JPL

Data as of Apr 17, 2026CSV

Voyager 1's plasma science instrument failed in 1980 and was formally shut down in 2007 [5]. The pace of deactivations has accelerated recently as the power budget has tightened:

• October 2024: Voyager 2's plasma science experiment was deactivated [5]
• February 25, 2025: Voyager 1's Cosmic Ray Subsystem (CRS) was turned off [6][7]
• March 24, 2025: Voyager 2's Low-Energy Charged Particle instrument was shut down [6]
• April 17, 2026: Voyager 1's LECP was deactivated [1]
• 2026 (planned): Voyager 2's Cosmic Ray Subsystem is scheduled for shutdown [6]

After the 2026 round of shutdowns completes, each Voyager will retain just two instruments: a magnetometer and a plasma wave subsystem [6]. JPL engineers believe the probes could continue operating with at least one science instrument into the 2030s, though that depends on the RTG output continuing to meet minimum thresholds [7].

"The Big Bang": A Last-Ditch Engineering Gambit

JPL engineers are not simply accepting the decline passively. They are developing what they internally call "the Big Bang" — a comprehensive energy-saving fix that would simultaneously replace multiple powered subsystems with lower-power alternatives in a single, coordinated operation [1].

Testing is scheduled to begin on Voyager 2 in May or June 2026, with a Voyager 1 implementation targeted for July 2026 or later [1]. The approach is high-risk: simultaneously modifying several systems on a spacecraft 15.5 billion miles away, with a 23-hour signal delay, offers little room for error. But if it works, it could extend the mission's scientific productivity by additional years.

The team has already demonstrated creative engineering under constraint. In 2023, NASA engineers tapped into a small reservoir of backup power set aside as part of an onboard safety mechanism, squeezing additional watts from a system designed for a different purpose [4].

What Science Is Being Lost

The LECP instrument measured the energy spectra, composition, and angular distributions of charged particles — ions and electrons — in the energy range from roughly 40 keV to 30 MeV [2]. In interstellar space, these particles include galactic cosmic rays and material from the local interstellar medium, the thin gas and dust between stars.

The Cosmic Ray Subsystem, shut down in February 2025, measured higher-energy cosmic rays and had provided data showing that plasma oscillation events in interstellar space are often preceded by relativistic cosmic ray bursts [8]. The loss of both instruments means Voyager 1 can no longer characterize the particle environment of interstellar space across its previous energy range.

What remains — the magnetometer and the plasma wave subsystem — still provides data of enormous scientific value. The plasma wave instrument has detected persistent, narrowband plasma wave emissions since 2017, enabling the first steadily sampled measurement of interstellar plasma density over about 10 astronomical units [8]. The magnetometer has registered abrupt changes in interstellar magnetic field intensity, including a jump in 2020 that scientists believe may indicate Voyager 1 passed through a small cloud of ancient interstellar plasma [9].

These measurements matter because they inform models of the heliosphere — the bubble of charged particles blown outward by the solar wind that shields the solar system from galactic cosmic radiation. The shape and dynamics of the heliosphere affect our understanding of how stars form, how cosmic rays propagate, and the radiation environment that future interstellar travelers would encounter [9].

The Only Eyes in Interstellar Space

Voyager 1 crossed the heliopause — the boundary where the solar wind gives way to interstellar plasma — on August 25, 2012, at about 122 astronomical units from the Sun [10]. Voyager 2 followed in November 2018. They remain the only human-made objects operating beyond the heliosphere.

No other spacecraft can replicate their measurements. The transition from solar-dominated to interstellar-dominated space proved far more complex than models had predicted — messy, gradual, and still not fully understood [10][11]. The Voyagers continue to reveal surprises, including unusual ripples at the heliopause boundary that remain unexplained [11].

"Every minute of every day, the Voyagers explore a region where no spacecraft has gone before," said Linda Spilker, Voyager project scientist [7].

Research interest in the Voyagers' interstellar data remains substantial. Academic publications referencing Voyager interstellar findings have grown from 85 papers in 2011 to a peak of 362 in 2023, with 155 published so far in 2026 [12].

Source: OpenAlex

Data as of Jan 1, 2026CSV

Multiple research communities depend on this data stream. Heliophysicists use the plasma density and magnetic field measurements to constrain models of the heliosphere's structure. Cosmic ray physicists rely on the particle data to understand how galactic cosmic rays are modulated by the heliosphere. Astrochemists study the composition of the interstellar medium. When the Voyagers go silent, these fields lose their only in situ data source beyond the heliopause [11].

A $5 Million Mission Under Budget Pressure

The Voyager Interstellar Mission costs approximately $5 million per year to operate — a fraction of the cost of virtually any other NASA science mission [13]. The original Voyager program, including both spacecraft, launch vehicles, and operations through the Neptune encounter, cost $865 million [13].

Yet even this modest budget has faced pressure. In late 2025, reports emerged that the Voyager project was facing a 26 percent budget cut, which would reduce annual funding to roughly $3.7 million [14]. An anonymous JPL insider told The Register: "We're a bit annoyed that Voyager has lost 26 percent of its budget... It's so bloody small... The whole thing is absolutely outrageous" [14].

The cuts came amid broader turmoil at JPL and across NASA, with proposed science budget reductions of up to 47 percent and potential layoffs of hundreds or thousands of employees [14][15]. Congress ultimately passed a $24.4 billion NASA budget that rejected many of the deepest proposed cuts [15], though the final allocation for Voyager operations specifically remains subject to agency discretion.

The Case for and Against Continued Investment

The case for extending the mission rests on irreplaceability. No other instrument, ground-based or space-based, can measure the local interstellar medium in situ. The data the Voyagers collect cannot be obtained any other way, and the cost of collecting it — $5 million a year — is orders of magnitude less than any conceivable replacement mission [13].

The Voyager probes also consume relatively little Deep Space Network time compared to newer missions, though their faint signals — transmitted at roughly 100 bits per second from over 15 billion miles away — require five large radio antennas and over 22 hours of tracking time to receive [16]. The DSN itself is under strain: over a five-year period, NASA missions collectively received between 8,500 and 15,000 fewer tracking hours than they requested [16].

The case for accelerated decommissioning is harder to find in public statements — few scientists or administrators want to be quoted arguing for shutting down what Suzanne Dodd, Voyager project manager, has called "deep space rock stars" [7]. But the argument exists implicitly in the budget numbers. Every dollar and every DSN hour allocated to Voyager is a dollar and hour unavailable to newer missions. New Horizons, which flew past Pluto in 2015, continues its own extended mission in the Kuiper Belt. The proposed Interstellar Probe, studied by the Johns Hopkins Applied Physics Laboratory, would carry modern instruments capable of far more sensitive measurements than the Voyagers' 1970s-era technology [17].

The practical question is whether the observational gap between the Voyagers' end of life and the Interstellar Probe's first data return is acceptable. Current projections place an Interstellar Probe launch between 2036 and 2041 [17]. At a minimum cruising speed roughly twice that of Voyager 1, the probe would still need years to reach the heliopause. A realistic estimate for the first in situ interstellar measurements from a successor mission is the 2060s at the earliest.

That means a potential gap of 30 years or more with no spacecraft operating in interstellar space — a gap during which humanity's only real-time window into conditions beyond the heliosphere would be closed [11][17].

Lessons for Future Long-Duration Missions

The Voyager power crisis is, in some respects, a success story. The RTGs were designed for a four-year primary mission; they have functioned for nearly 49 years. The engineering margins built into the system — the backup power reservoirs, the modular instrument architecture that allows piecemeal shutdown — have proven remarkably durable.

No other space agency has faced a comparable challenge. ESA's longest-running deep space missions, such as the Ulysses solar probe (launched 1990, decommissioned 2009), used RTGs of similar design but did not approach the Voyagers' longevity [3]. The European Space Agency's Rosetta mission operated for 12 years on solar power before its planned end of mission in 2016. Neither case involved the decades-long power triage that the Voyager team now manages annually.

The lessons are directly relevant to the proposed Interstellar Probe, which would need to operate for 50 to 100 years [17]. Power system design, instrument modularity, and the ability to gracefully degrade over multi-decade timescales will be central engineering challenges. The Voyager experience — both its successes and its current constraints — provides the only real-world dataset for that design process.

What Comes Next

For now, Voyager 1 continues transmitting with its two remaining instruments. Each measurement of interstellar magnetic field strength, each detection of plasma wave oscillation, adds to a dataset that no other mission has produced or will produce for decades.

The "Big Bang" power-saving operation, if successful, could extend that timeline. But the underlying physics is unyielding. The plutonium will continue to decay. The power will continue to drop. And at some point — likely in the early-to-mid 2030s — the last instrument will go silent, and the most distant human-made object will become a silent artifact, drifting through the galaxy at 38,000 miles per hour, carrying a golden record and the accumulated momentum of a civilization that, for a brief window, managed to listen to the space between the stars.