Launched in 1977, Voyager 1 and 2, initially sent to explore the outer planets, ultimately became the first human-made objects to enter interstellar space.
Currently, Voyager 1 is over 15 billion miles away (25 billion kilometers), and Voyager 2 is over 13 billion miles away (21 billion kilometers).
The twin explorers carry a suite of scientific instruments to gather invaluable data about the interstellar medium. But time and distance take their toll.
They lose about four watts of power per year due to the gradual decay of their radioisotope power source.
Mission engineers at NASA’s Jet Propulsion Laboratory face a critical challenge: how to keep these aging spacecraft alive for as long as possible.
To conserve energy, instruments are being selectively deactivated. On February 25th, Voyager 1’s cosmic ray subsystem was shut down. On March 24th, Voyager 2’s low-energy charged particle instrument will follow.
“The Voyagers have been deep space rock stars since launch, and we want to keep it that way as long as possible,” said Suzanne Dodd, Voyager project manager at JPL.
“But electrical power is running low. If we don’t turn off an instrument on each Voyager now, they would probably have only a few more months of power before we would need to declare end of mission,” Dodd added.
Far surpassed the original missions
Each of the two spacecraft has 10 identical instruments, but only three will remain active now.
NASA has been strategically deactivating Voyager instruments based on operational necessity and the observed decline in instrument functionality.
For instance, the instruments on the Voyager spacecraft designed for planetary flybys were deactivated after their gas giant exploration. Also, the plasma instruments on both probes were deactivated for these reasons.
Voyager 1’s cosmic ray subsystem, a set of three telescopes, was recently shut down. It measured cosmic rays, and its data was crucial in determining when Voyager 1 entered interstellar space.
While Voyager 2’s low-energy charged particle instrument analyzes ions, electrons, and cosmic rays. It contains two parts: a telescope for general energy measurements and an analyzer for detailed magnetospheric studies.
The instruments on Voyager 2 use a rotating platform for a complete 360-degree view, powered by a 15.7-watt motor that pulses.
Originally designed to last through the Saturn encounter (1980), the motor has far exceeded expectations, completing over 8.5 million steps before its upcoming deactivation.
“The Voyager spacecraft have far surpassed their original mission to study the outer planets,” said Patrick Koehn, Voyager program scientist at NASA Headquarters in Washington.
Koehn added: “Every bit of additional data we have gathered since then is not only valuable bonus science for heliophysics, but also a testament to the exemplary engineering that has gone into the Voyagers — starting nearly 50 years ago and continuing to this day.”
NASA aims to operate the twin probes till the 2030s
After these shut down, NASA plans to deactivate other ones also.
Voyager 1 will continue to use its magnetometer and plasma wave subsystem. Its low-energy charged particle instrument will remain active until the end of 2025, and then it will be deactivated.
Voyager 2’s magnetic field and plasma wave instruments will remain active, while its cosmic ray subsystem will be deactivated in 2026.
NASA hopes the Voyager probes can continue operating at least one instrument into the 2030s. However, NASA acknowledges the probes’ age and that unexpected issues could shorten operations.
“Every minute of every day, the Voyagers explore a region where no spacecraft has gone before,” said Linda Spilker, Voyager project scientist, in the press release.
“That also means every day could be our last. But that day could also bring another interstellar revelation. So, we’re pulling out all the stops, doing what we can to make sure Voyagers 1 and 2 continue their trailblazing for the maximum time possible,” Spilker added.