NASA engineers have brought a set of obsolete thrusters back from the dead on the Voyager 1 probe, just before losing their ability to talk to the aging spacecraft.
Over a half-century, Voyager 1 has sprinted about 38,000 mph and become the farthest human-made object, crossing into interstellar space. For the past two decades of its journey, the spacecraft has come to rely on a special set of backup thrusters that are designed to control its roll motion. But those backups have begun to clog with gunk, and no one is sure how much longer they'll last — perhaps mere months.
Meanwhile, a powerful antenna in Australia — the only one capable of sending instructions to Voyager 1 now 15.5 billion miles from Earth — was about to go offline for critical upgrades. NASA feared if those backups failed during the monthslong blackout, the team would forever lose their fragile link to the spacecraft.
So engineers crafted a risky plan to attempt a resurrection of the primary roll thrusters that the team had all but given up on in 2004. Those small engines help spin the spacecraft just enough to keep it pointed at a guide star for orientation. Without them, Voyager 1 would be as good as gone.
"At that time, the team was OK with accepting that the primary roll thrusters didn’t work, because they had a perfectly good backup," said Kareem Badaruddin, Voyager mission manager, in a statement. "And, frankly, they probably didn’t think the Voyagers were going to keep going for another 20 years."
Both Voyager 1 and its twin, Voyager 2, have far outlived their original life expectancy. Launched in 1977, the pair was originally intended to study Jupiter and Saturn, their moons, and Saturn's rings. For the two-planet journey, they were built to operate for just five years.
After their initial success, engineers doubled their objectives to include two more giant planets, Uranus and Neptune. Between the two spacecraft, they've explored four planets, 48 moons, and a host of planetary magnetic fields and rings. Now they're in the cold, uncharted abyss.
In August 2012, Voyager 1 made history as it entered interstellar space, the region between stars, filled with material ejected by other stars that died millions of years ago. Voyager 1 and 2 are the only spacecraft ever to fly outside of the heliosphere, the region of space affected by the sun's constant flow of radiation and particles.
But after 48 years hurtling through the unknown, their systems are wearing down. The primary roll thrusters stopped working 21 years ago, after losing power in two small internal heaters. Engineers at the time thought that meant they were inoperable.
"That was a legitimate conclusion," said Todd Barber, the mission’s propulsion lead, in a statement. "It’s just that one of our engineers had this insight that maybe there was this other possible cause and it was fixable."
This Tweet is currently unavailable. It might be loading or has been removed.
The team pondered whether a disruption in the heaters' circuits had essentially flipped a switch to an off position. If they could turn it back, the heaters might work again.
To try it, the team would have to turn on the broken thrusters, then try to restart the heaters. If, during that time, the spacecraft drifted too far off course, the broken thrusters would automatically fire, due to their programming. The danger there would be if the heaters were still not working, they could trigger a small explosion.
But within 20 minutes of attempting the fix, the team saw the heaters' temperature rise dramatically, signaling success.
"It was such a glorious moment. Team morale was very high that day," Barber said. "It was yet another miracle save for Voyager.”
As of May 4, the Australian antenna — part of NASA’s Deep Space Network, a system of three enormous radio dish arrays on Earth — is offline. It'll remain dark until February 2026, with only brief periods of operation in August and December.
The antenna upgrades are necessary for Artemis astronaut moon landings and will increase communication capacity for deep space robotic missions, said Suzanne Dodd, who oversees Voyager and the Deep Space Network.
Voyager 1 is so far away, it takes 23 hours for a command to reach the spacecraft, and another 23 hours for mission control to hear back from it. NASA has previously said the Voyagers generate about 4 fewer watts of power annually, limiting the number of systems the spacecraft can use. The teams have occasionally turned off equipment to conserve power.
NASA says the goal is to keep the two missions afloat beyond 2025.
