NASA's Voyager 1 Revives Backup Thrusters Before Command Pause

NASA's Voyager 1 Revives Backup Thrusters Before Command Pause
by Staff Writers
Pasadena CA (JPL) May 15, 2025

The mission team wanted to fix the thrusters, deemed unusable decades ago, before the radio antenna that sends commands to the probe went offline for upgrades.

Engineers at NASA's Jet Propulsion Laboratory in Southern California have revived a set of thrusters aboard the Voyager 1 spacecraft that had been considered inoperable since 2004. Fixing the thrusters required creativity and risk, but the team wants to have them available as a backup to a set of active thrusters whose fuel tubes are experiencing a buildup of residue that could cause them to stop working as early as this fall.

In addition, the mission needed to ensure the availability of the long-dormant thrusters before May 4, when the Earth-bound antenna that sends commands to Voyager 1 and its twin Voyager 2 went offline for months of upgrades.

Thruster Clogging

The Voyagers launched in 1977 and are hurtling through interstellar space at around 35,000 mph (56,000 kph). Both spacecraft rely on a set of primary thrusters to gently pivot them up and down as well as to the right and left in order to keep their antennas pointed at Earth so they can send back data and receive commands. Within the primary set of thrusters are other thrusters that control the spacecraft's roll motion. Seen from Earth, the roll motion rotates the antenna like a vinyl record to keep each Voyager pointed at a guide star it uses to orient itself. Both spacecraft have a primary and backup set for these roll movements.

(Another set of thrusters, intended to change the spacecrafts' trajectory during the flybys of the outer planets, were revived on the spacecraft in 2018 and 2019, but they can't induce roll motion.)

To manage the clogging tubes in the thrusters, engineers switch between the sets of primary, backup, and trajectory thrusters of both Voyagers. But on Voyager 1, the primary roll thrusters stopped working in 2004 after losing power in two small internal heaters. Engineers determined the broken heaters were likely unfixable and opted to rely solely on Voyager 1's backup roll thrusters to orient the star tracker.

"I think 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 at JPL, which manages the mission for NASA. "And, frankly, they probably didn't think the Voyagers were going to keep going for another 20 years."

But without the ability to control the spacecraft's roll motion, a variety of issues would arise that might threaten the mission, so the engineering team decided to reexamine the 2004 thruster failure. They began to suspect that an unexpected change or disturbance in the circuits that control the heaters' power supply had effectively flipped a switch to the wrong position. If they could turn the switch back to its original position, the heaters might work again, enabling them to reactivate the primary roll thrusters and use them if the backup roll thrusters that have been used since 2004 become completely clogged.

Communications Pause

The solution required some puzzle-solving. The team would have to turn on the dormant roll thrusters, then try fixing and restarting the heaters. If, during that time, the spacecraft's star tracker drifted too far from the guide star, the long-dormant roll thrusters would automatically fire (thanks to the spacecraft's programming). And if the heaters were still off when they fired, it could trigger a small explosion, so the team needed to get the star tracker pointed as precisely as possible.

It would be a race, and the team faced additional time pressure: From May 4, 2025, through February 2026, Deep Space Station 43 (DSS-43), a 230-foot-wide (70-meter-wide) antenna in Canberra, Australia, that's part of NASA's Deep Space Network, would be undergoing upgrades. It would be offline for most of that time, with brief periods of operation in August and December.

Although the Deep Space Network has three complexes equally spaced around the globe (in Goldstone, California, and Madrid, in addition to Australia) to ensure constant contact with spacecraft as Earth rotates, DSS-43 is the only dish with enough signal power to send commands to the Voyagers.

"These antenna upgrades are important for future crewed lunar landings, and they also increase communications capacity for our science missions in deep space, some of which are building on the discoveries Voyager made," said Suzanne Dodd, Voyager project manager and director of the Interplanetary Network at JPL, which manages the Deep Space Network for NASA. "We've been through downtime like this before, so we're just preparing as much as we can."

The team wanted to make sure the long-dormant thrusters would be available when the dish is back online briefly in August, by which time the thrusters currently in use on Voyager 1 might be completely clogged.

The advance work paid off: On March 20, the team watched as the spacecraft executed their commands. Because of Voyager's distance, the radio signal takes over 23 hours to travel from the spacecraft to Earth, meaning everything the team saw happening had occurred almost a day earlier. If the test had failed, Voyager might already have been in danger. But within 20 minutes, the team saw the temperature of the thruster heaters rise dramatically and knew they had succeeded.

"It was such a glorious moment. Team morale was very high that day," said Todd Barber, the mission's propulsion lead at JPL. "These thrusters were considered dead. And that was a legitimate conclusion. It's just that one of our engineers had this insight that maybe there was this other possible cause and it was fixable. It was yet another miracle save for Voyager."