The two Voyager probes are slowly running out of power, and the engineers keeping them alive are now making the hardest decisions of the mission: which scientific instruments to switch off next, knowing each command may silence a piece of interstellar science forever. – Image for illustrative purposes only (Image credits: Unsplash)
After nearly five decades in flight, the Voyager 1 and Voyager 2 spacecraft have reached a point where every remaining watt of power carries a permanent cost. Engineers at NASA’s Jet Propulsion Laboratory must now decide which of the last scientific instruments to deactivate, knowing that each command sent across billions of miles will silence measurements that cannot be recovered. The decisions reflect both the extraordinary longevity of the mission and the steady decline of the probes’ nuclear power sources. What began as a planetary tour has become a careful exercise in preserving the most irreplaceable data from the space between the stars.
The Probes’ Shrinking Scientific Reach
As of May 2026, Voyager 1 operates with only its magnetometer and Plasma Wave Subsystem still collecting data. Voyager 2 retains three instruments but is scheduled to lose its Cosmic Ray Subsystem later this year, leaving both spacecraft with the same minimal pair. The sequence of recent shutdowns has followed a deliberate schedule rather than sudden emergencies. Voyager 2’s plasma science instrument was turned off in September 2024, followed by Voyager 1’s cosmic ray subsystem in February 2025 and its Low-Energy Charged Particle instrument in April 2026.
Each shutdown command travels between 20 and 23 hours to reach the spacecraft, and the team treats every deactivation as likely permanent. One narrow exception exists for Voyager 1’s Low-Energy Charged Particle instrument, where a small stepper motor continues to run at roughly half a watt to preserve a slim possibility of future reactivation. That motor has already completed more than 8.5 million steps, far beyond its original design life of about 500,000.
Why Certain Instruments Were Protected Longest
The order of shutdowns was not chosen in the moment. Years ago, the science and engineering teams created a ranked list based on which measurements still held unique value once the spacecraft left the solar system. Instruments that had finished their primary work during the planetary encounters of the 1970s and 1980s were retired first. The two systems kept until the end – the magnetometer and the Plasma Wave Subsystem – provide direct readings of the interstellar magnetic field and plasma density that no other mission currently duplicates.
Project manager Suzanne Dodd has described the trade-off in clear terms: without turning off an instrument on each Voyager now, the spacecraft would likely lose all power within a few additional months. The choice is therefore between selective shutdowns and an earlier end to the entire mission. This approach allows the probes to continue returning at least some interstellar data for as long as possible.
What the Remaining Power Buys
Most instrument shutdowns involve simply cutting the power feed, after which the device is removed from the active set with no realistic path to restoration. The single ongoing exception on Voyager 1 illustrates how narrowly the team balances risk and reward. By keeping the stepper motor turning, engineers maintain a mechanical link that could, under changed power conditions, allow the Low-Energy Charged Particle instrument to resume limited operations.
After the Cosmic Ray Subsystem on Voyager 2 is deactivated later in 2026, both probes will operate with identical minimal instrument suites. The next phase will involve deciding which of the two remaining instruments to retain on each spacecraft and when to make those final cuts. A separate engineering test called the Big Bang plan is also scheduled for Voyager 2 in May and June 2026; if successful, it could swap older components for lower-power alternatives and potentially extend at least one science instrument into the 2030s.
Key Milestones Still Ahead
Several concrete events will shape the mission’s final years. The outcome of the Big Bang test on Voyager 2 will determine whether similar steps can be taken on Voyager 1. The Cosmic Ray Subsystem shutdown on Voyager 2 remains the next firm date on the calendar. Further out, the point at which only engineering telemetry continues to reach Earth will mark the transition from science return to basic spacecraft health monitoring.
- Big Bang procedure test on Voyager 2 (May–June 2026)
- Cosmic Ray Subsystem deactivation on Voyager 2 (later 2026)
- Possible engineering-only signal until around 2036
The four watts lost each year impose a non-negotiable limit. The choices made between now and the early 2030s will determine which specific questions about the interstellar medium can still be answered and which must be left for future missions. Those decisions rest with a small team that has already guided the spacecraft farther than any other human-made objects in history.