NASA pulls another life-saving maneuver for Voyager from 15 billion miles away

The farthest-flung human-made objects will be able to take their mission even farther, thanks to a series of power-saving decisions. On February 25, engineers turned off the cosmic ray subsystem experiment on Voyager 1, and on March 24, they will deactivate Voyager 2’s low-energy charged particle instrument. 

Three science instruments will remain active on each spacecraft, enabling the twin probes to keep transmitting data from interstellar space despite an ever-declining power supply.

Energy challenges in deep space

Voyager 1 and Voyager 2, launched in 1977, rely on a radioisotope thermoelectric generator that converts the heat from decaying plutonium into electricity. Each spacecraft loses about 4 watts of power every year. 

The project team, led by NASA’s Jet Propulsion Laboratory (JPL), has been gradually switching off instruments and systems to manage this dwindling energy, which is critical to the continued operation of the probes’ most important science instruments.

“The Voyagers have been deep space rock stars since launch, and we want to keep it that way as long as possible. But electrical power is running low,” said Suzanne Dodd, Voyager project manager at JPL.

“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.”

Reducing Voyager’s instrument load

Each spacecraft originally carried ten instruments, many of which were designed to study Jupiter, Saturn, Uranus, and Neptune during flybys in the 1980s. 

Over the decades, after the planetary portion of the mission concluded, several instruments were deactivated, leaving the ones needed to investigate the heliosphere – the bubble of charged particles and magnetic fields generated by the Sun – and interstellar space, where both Voyagers are now traveling. 

Voyager 1 crossed into interstellar space in 2012, followed by Voyager 2 in 2018, making them the only spacecraft to operate in that unknown realm.

Engineers decided in October to turn off Voyager 2’s plasma science instrument, which measures plasma flow but had collected limited recent data due to its orientation.

Voyager 1’s version of this instrument had been switched off years ago for performance reasons. 

Now, the team has also shut down Voyager 1’s cosmic ray subsystem experiment, which consisted of three telescopes that studied energetic particles from the Sun and the wider galaxy.

The data from that experiment was essential for pinpointing Voyager 1’s crossing from the heliosphere into interstellar space.

Key instruments going offline

Next, the team will shut down the low-energy charged particle instrument on Voyager 2, which examines ions, electrons, and cosmic rays.

The instrument includes two subsystems: a low-energy particle telescope for broad energy measurements, and a low-energy magnetospheric particle analyzer for specialized studies. 

Both components rely on a rotating platform powered by a stepper motor that draws 15.7 watts every 192 seconds.

That motor was tested to last through the spacecraft’s Saturn encounter in 1980, but by the time the instrument is powered off, it will have performed more than 8.5 million steps.

“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. 

“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.”

Sustaining deep space exploration

Mission engineers have chosen to deactivate as few scientific instruments as possible because the probes deliver unique observations from the edge of the solar system.

By carefully rationing power, they expect both Voyagers to keep collecting data for at least another year before more instruments must be switched off. 

Voyager 1 will continue operating its magnetometer and plasma wave subsystem, while its low-energy charged particle instrument will remain on through 2025 and then be switched off.

Voyager 2 will keep running its magnetic field and plasma wave instruments, with its cosmic ray subsystem slated for shutdown in 2026.

Implementing this new power management approach should allow each spacecraft to keep at least one instrument functioning into the 2030s.

However, the team acknowledges that the Voyagers, which have traveled for 47 years, could face unanticipated problems that shorten that timeline.

The trailblazing Voyager mission

Voyager 1 is currently more than 15 billion miles (25 billion kilometers) from Earth, and Voyager 2 is over 13 billion miles (21 billion kilometers) away.

Communicating with them is a slow process, taking about 23 hours for a signal to reach Voyager 1 and more than 19 hours to reach Voyager 2.

“Every minute of every day, the Voyagers explore a region where no spacecraft has gone before,” said Linda Spilker, Voyager project scientist at JPL. 

“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,” she concluded.

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