- NASA's Voyager 1 and 2 are the only human-made objects to reach interstellar space.
- The two probes launched in 1977 and may soon lose communication with Earth.
In 1977, NASA launched Voyager 1 and 2 for what was meant to be four-year missions. For over 46 years, the pair have been delivering spectacular science far beyond what their first teams of researchers could have hoped.
From close-up views of Jupiter to a stunning look a Saturn's rings, the Voyager probes have helped shape our understanding of the solar system. Voyager 2 is still the only spacecraft to visit Uranus and Neptune. They've traveled further from Earth than any other human-made object.
Solar wind streaming out from the sun and interstellar wind flowing back toward it creates a bubble known as the heliosphere. In 2012, Voyager 1 ventured beyond the heliosphere into interstellar space. Voyager 2 followed in 2018.
Both probes are slowly draining power and will soon lose contact with Earth.
But NASA is coming up with unique solutions to keep communicating with the two Voyagers.
"That's what's most important is keeping these spacecraft operating as long as possible," Suzanne Dodd, NASA's project manager for Voyager, told Business Insider.
Decades of data
Early in their travels, the two spacecraft parted ways. Voyager 1 is now 15 billion miles away from Earth, and Voyager 2 is 12 billion.
As the probes journey further from our planet, their data becomes more and more valuable. The Voyagers are picking up information on charged particles in interstellar space, including their energy levels, their abundance, and the direction of their magnetic fields.
"They're out of the effects of charged particles from our sun and truly measuring data in interstellar space and measuring how that data changes as they travel further away from us," Dodd said.
She compares it to seeing the difference between waves breaking on the shore and smoothing out deeper in the ocean.
"You would never know that unless you got further out of the ocean, how those waves change," she said.
It would take another 50 years for another vehicle to reach interstellar space, Dodd said. That's why the Voyagers are so valuable.
"They're doing very unique science," she said.
NASA has been turning instruments off to conserve power
The nuclear-powered Voyagers use radioisotope thermoelectric generators that turn heat from decaying plutonium-238 into energy. Originally, the generators provided around 450 watts of power, Dodd said.
Each year, as the plutonium decays, the generators produce about 4 watts less.
"They're down to about 220 watts of power available," Dodd said. Operating the probes' transmitters requires about 200 watts. Their instruments can use as much as 6 watts each.
Voyager 1 currently has four instruments running, and Voyager 2 has five.
To conserve power, engineers have shut off heaters and powered down other systems. "We've done a lot of clever engineering things to be able to keep these instruments on as long as possible, knowing that we have a limited power supply," Dodd said.
"Something could fail that would be catastrophic kind of at any time," she added.
There have been a few near-misses, like when both probes nearly failed at launch and when NASA lost communication with Voyager 2 for a few weeks in the summer of 2023.
By 2026, NASA may have to turn off at least one of Voyager 2's instruments.
"What we're looking at is making the two spacecraft complementary to each other," Dodd said. "You might keep one instrument operating on one spacecraft but turn it off on another."
Down the road, the choices about which instruments to keep running will be more difficult. Dodd said the scientists will likely keep powering the ones that take the least energy.
"And then it's also an evaluation of the science," she said. "What's the most critical science that we get?"
Even after the spacecraft power down, they have one more mission left
When the spacecraft lose communication with Earth, it will be the end of the mission, Dodd said.
But the Voyagers will continue traveling, Dodd said, perhaps for hundreds of thousands of years.
"They'll just be floating out in space and floating around the center, traveling away from us with a gold record that, hopefully, some being, somewhere will find in the future."
The golden records are phonographs containing images, words, and music meant to explain human life to aliens. Each Voyager probe has a copy.
In the meantime, Dodd isn't quite ready to say goodbye to the Voyagers.
"It's pretty remarkable, into our 47th year, just the whole record of discoveries it's made," she said.
The fact that there are two spacecraft means the chances are pretty good that at least one of them can keep communicating for a few more years, Dodd said.
"I'm very optimistic that we'll get to a 50-year anniversary," she said.