NASA has shut down another instrument on Voyager 1, the most distant spacecraft made by humans. The NASA Jet Propulsion Laboratory (JPL) said on the 17th (local time) that it sent a command to Voyager 1 to turn off the low-energy charged particle instrument (LECP). With this step, only two science instruments remain operating on Voyager 1: the magnetometer and the plasma wave instrument.
Voyager 1 was launched in 1977. The spacecraft's original mission was to pass by Jupiter and Saturn and send back data. However, after completing that mission, it kept flying and in 2012 left the "heliosphere," the vast region influenced by the solar wind and magnetic field, and entered interstellar space. The only artifacts now sending direct observational data from interstellar space are Voyager 1 and its twin probe, Voyager 2.
◇ The biggest enemy is not failure but power shortage
Voyager 1's biggest problem is a lack of power. The probe uses a radioisotope power system that converts heat from plutonium decay into electricity, rather than solar cells. The device has the advantage of a long lifespan, but its output declines slightly each year. NASA says Voyager 1 is losing about 4W (watts) of power annually.
For years, the research team has planned which instruments to shut down and in what order to keep the probe's mission going as long as possible. If the voltage falls below a certain level, the probe's protection system will shut off several devices on its own, and that can make recovery long and risky.
In 1990, Voyager 1's cameras were turned off to save power, followed by the infrared instrument in 1998 and the ultraviolet spectrometer in 2016. The cosmic ray subsystem (CRS) was also turned off in February last year to conserve power. More recently, when Voyager 1's power dropped more than expected during rotation for attitude control, the probe proactively shut down the LECP.
Beyond that, Voyager 1 has weathered numerous hurdles over half a century. In Nov. 2023, when the flight data system (FDS) memory was partially damaged, it sent only unreadable data to Earth, and only in Apr. 2024 did it begin transmitting decodable status information again. Engineers used a method of moving the relevant code into different memory locations. In Oct. 2024, when Voyager 1's protection system activated, the main X-band transmitter was turned off and the weaker S-band transmitter was turned on. The S-band uses less power but its signal is much weaker, making it hard to send data reliably to Earth. The research team revived the X-band transmitter in late Nov. of the same year.
The probe's distance makes such repairs even harder. Voyager 1 is already more than 15 billion miles (about 24.1 billion km) from Earth. It takes more than 23 hours for radio commands sent from Earth to reach Voyager 1. In the end, it takes almost two days just to send a command to Voyager 1 and confirm the result.
◇ First to reach 1 light-day ahead… "Could last into the 2030s"
Voyager 1 is expected to become the first in human history to reach a distance of 1 light-day from Earth in Nov. 2026. One light-day is the distance light travels in a day, about 25.9 billion km. When Voyager 1 gets there, it will take a full day just for radio commands sent from Earth to arrive.
So how much farther can Voyager 1 go? In March last year, NASA announced a power-saving plan, saying that if instruments are turned off sequentially, Voyager 1 could maintain at least one science instrument and possibly last into the 2030s.
A 2023 NASA Heliophysics Senior Review report reached a similar conclusion. The report said that continuing the approach of shutting down instruments in sequence and using creative power management could extend the life of the overall Voyager mission into the mid-2030s. However, this outlook assumes there are no major failures.
The research team is now preparing a "Big Bang" plan to further cut Voyager's power consumption. The plan is to swap multiple power-using devices at once—turning some off, replacing others with lower-power alternatives—and keep the spacecraft sufficiently warm. NASA plans to apply the plan first to Voyager 2, which has a bit more power to spare, and if successful, try it on Voyager 1 around July this year. Voyager 2 is closer to Earth than Voyager 1.