NASA patched its Voyager 2 spacecraft last week, to address a bug that last year saw its sibling generate corrupted telemetry data, but won't know if its fix worked - or overwrote critical code - until some time after October 28.

Both Voyagers were launched in 1977. Voyager 1 is now more than 22 billion kilometers (15 billion miles) from Earth, and almost 22 and a half light hours away. Voyager 2 is over 20 billion kilometers from home (12.5 billion miles) and more than eighteen hours and forty minutes away at the speed of light. The two probes have left our solar system and communication is therefore very slow - 160 bits per second to Voyager 1 as of May 2022.

NASA already figured out that the cause of the garbled data on Voyager 1 was the attitude articulation and control system (AACS) - a tool that controls the crafts' orientation, including keeping their antennae pointed precisely at Earth.

In a Friday post, NASA's Jet Propulsion Laboratory explained that the AACS was writing commands into memory instead of carrying them out. "One of those missed commands wound up garbling the AACS status report before it could reach engineers on the ground," the post states.

"The team determined the AACS had entered into an incorrect mode; however, they couldn't determine the cause and thus aren't sure if the issue could arise again. The software patch should prevent that," the document continues.

JPL's Voyager project manager Suzanne Dodd explained that months of effort went into creating a patch, which was sent to Voyager 2 last Friday.

"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," she warned. Voyager 2 is therefore the first target for the patch, because it's closer to Earth - which matters for two reasons.

For starters, communication with Voyager 2 is quicker, making uploads and tests a little easier.

NASA also rates Voyager 1's data more valuable, as it is farther from home. Messing up Voyager 2, while undesirable, is more acceptable.

The patch was despatched to Voyager 2 on October 20 and NASA plans to test it on the 28th.

Fuel problems

NASA also made a change to address problems with the Voyagers' thrusters, which aren't in peak condition as the propellant inlet tubes that bring them fuel have accumulated a "significant" buildup of residue.

The space agency has therefore begun letting the two spacecraft rotate slightly farther in each direction before firing the thrusters, as doing so 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 one degree farther in each direction than in the past," reads the October 20 post. "The mission is also performing fewer, longer firings, which will further reduce the total number of firings done on each spacecraft."

The post explains that NASA has had to make a trade-off, because rotating the spacecraft more means some data doesn't make it to Earth. But mission boffins "concluded the plan will enable the Voyagers to return more data over time."

"Engineers can't know for sure when the thruster propellant inlet tubes will become completely clogged, but they expect that with these precautions, that won't happen for at least five more years, possibly much longer," the post adds.

Given Voyager's engineers have kept the two probes going far, far, longer than expected, who would bet against them finding new ways to extend their lives? ®

https://www.theregister.com//2023/10/23/nasa_voyager_upgrades/