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Voyager 1 fires thrusters last used in 1980 – and they worked!

Ancient assembler code checked out and now probe's mission can be extended

NASA's announced that Voyager 1's already-amazingly-long mission will probably be extended for an extra two or three years, thanks to a successful attempt to use thrusters that haven't fired up since the year 1980.

As NASA announced last Friday, Voyager 1's been using its “attitude control thrusters” (ACMs) for decades, to nudge the probe so that its antenna points at Earth and it can stay in touch.

While the ACMs work, since 2014 they've use more fuel than in the past. As Voyager 1 carries a finite quantity of fuel, thirsty thrusters are not welcome.

The probe does, however, have other thrusters – its "trajectory correction maneuver” (TCM) thrusters were last used as it passed Saturn, to help point Voyager 1's instruments at the ringed gas giant. As the TCMs are mounted on the craft's rear and Voyager doesn't need a speed boost – it's already doing 17.46 km/second – they've been left alone since 1980.

But Voyager's masters felt the ailing ACMs meant it was worth trying to see if the TCMs could pick up the slack.

Voyager mission logo

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Testing that hypothesis was a job for software developers, as Jet Propulsion Laboratory chief engineer Chris Jones said “The Voyager flight team dug up decades-old data and examined the software that was coded in an outdated assembler language, to make sure we could safely test the thrusters."

Helping things out was the fact that the same model of thruster used on Voyager 1 was later deployed on Cassini and Dawn probes, meaning NASA had experience with the hardware.

So last Tuesday, November 28th, the Voyager team told the far-off probe to fire the TCM thrusters. And late the next day – after a 38-hour radio round trip - they learned that they worked and did the job just as well as the ACMS.

"With these thrusters … we will be able to extend the life of the Voyager 1 spacecraft by two to three years," said Suzanne Dodd, project manager for Voyager. She added that the Voyager team is so chuffed with the result, they may test the TCMs on Voyager 2, too, even though its ACMs continued to perform well.

Both Voyagers are powered by radioisotope thermoelectric generators, devices that can turn heat into electricity, but which also degrade over time. NASA plans to switch off the Voyagers' instruments as their generators deplete, eventually leaving just the radios. Once even they stop working, the craft have enough momentum to keep sailing on into the Galaxy, complete with their golden records that attempt to explain humanity, until something nasty stops them. ®

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