The NASA Voyager team prioritizes addressing a software patch and maintaining the thrusters.

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These efforts will help extend the lifespan of the agency's interstellar explorers.

Engineers on NASA's Voyager mission are taking steps to ensure that the two spacecraft, launched in 1977, continue to explore interstellar space for years to come.

An effort is underway to address fuel residue that appears to be accumulating inside narrow tubes in some spacecraft thrusters. Thrusters are used to keep each spacecraft's antenna pointed toward Earth. This type of accumulation has been observed in several other spacecraft.

The team is also releasing a software patch to prevent a recurrence of the problem that occurred on last year's Voyager 1. Engineers have fixed the problem, and the fix is ​​intended to prevent the problem from recurring in Voyager 1 or  its twin, Voyager 2.

Thruster Buildup

The thrusters of Voyager 1 and Voyager 2 are primarily used to keep the spacecraft's antennas pointed at Earth for communications. The spacecraft can rotate in three directions: up and down, left and right and around the central axis, like a wheel. As they do so, the thrusters will automatically fire and reorient the spacecraft to keep their antennas pointed at Earth.

The propellant reaches the thrusters through the fuel lines, then passes through smaller passages inside the thrusters called propellant ducts that are 25 times narrower than the external fuel lines. Each propellant shot adds a small amount of propellant residue, leading to a gradual buildup of material over decades. In some of the propellant inlet tubes, the buildup is becoming significant. To slow that buildup, the mission has begun letting the two spacecraft rotate slightly farther in each direction before firing the thrusters. This will reduce the frequency of thruster firings.

The adjustments to the thruster rotation range were made by commands sent in September and October, and they allow the spacecraft to move almost 1 degree farther in each direction than in the past. The mission is also performing fewer, longer firings, which will further reduce the total number of firings done on each spacecraft.

Adjustments have been carefully designed to ensure minimal impact to the mission. Although the spacecraft's greater rotation speed could lead to occasional pieces of science data being lost – such as during a phone call where the person on the other end occasionally interrupts – the team concluded that the plan would allow the astronauts to return more data overtime.

Engineers can't know for sure when the thruster's propellant pipes will become completely clogged, but they hope that with these precautions, it won't happen for at least five years, It could be many years from now. The team may take additional steps in the coming years to extend the life of the thrusters even further.

“This far into the mission, the engineering team is being faced with a lot of challenges for which we just don’t have a playbook.”, said Linda Spilker, project scientist for the mission as NASA’s Jet Propulsion Laboratory in Southern California. “But they continue to come up with creative solutions.”

In 2022, the onboard computer navigating Voyager 1 to Earth began sending back garbled status reports, although it continued to function normally. It took months for mission engineers  to identify the problem. The 'AACS' Articulation and Attitude Control System' commands are misdirected, writing them to computer memory instead of executing them. One of these missed commands corrupted the AACS status report before it could reach engineers in the field.

The team determined that AACS had entered  an incorrect mode; However, they were unable to determine the cause and were therefore unsure whether the problem could recur. The software patch should prevent that.

“This patch is like an insurance policy that will protect us in the future and help us keep these probes going as long as possible,” said JPL's Suzanne Dodd, Voyager project manager. “These are the only spacecraft to ever operate in interstellar space, so the data they're sending back is uniquely valuable to our understanding of our local universe.”

Voyager 1 and Voyager 2 have traveled more than 15 billion and 12 billion miles from Earth, respectively. At those distances, the patch instructions will take over 18 hours to travel to the spacecraft. Because of the spacecraft's age and the communication lag time, there's some risk the patch could overwrite essential code or have other unintended effects on the spacecraft. To mitigate these risks, the team  spent months writing, reviewing, and verifying the code. As an added security measure, Voyager 2 will receive the patch first and serve as a testing ground for its twin. Voyager 1 is farther from Earth than any other spacecraft, making its data even more valuable.

The team will download the patch and perform an AACS memory read to ensure it is in the correct location on Friday October 20. If no immediate issues arise, the team will issue a command on Saturday, Oct. 28, to see if the patch is operating as it should.