NASA’s twin Voyager probes have been on a mission of exploration for decades, and they’ve performed admirably. Both probes have now left the solar system, providing the first direct measurements of the universe outside our little corner of it. Keeping a 42-year-old space probe working is no simple feat, though. Engineers are working to restore normal operations on Voyager 2 after automated fault protection routines shut off the probe’s science instruments.
While Voyager 2 was the first of the two probes to leave Earth back in 1977, it took a more roundabout course out of the solar system. It remains the only spacecraft to visit both Saturn and Neptune, which kept it from reaching the interstellar medium until 2018. Voyager 1, on the other hand, left the solar system back in 2012.
The first sign of trouble came on January 25th when the spacecraft failed to execute a planned maneuver to calibrate its magnetic field instrument. Voyager 2 remained in contact with Earth, but its science instruments shut off after the failed maneuver. After studying the probe’s telemetry, the team determined that the missed spin left two high-power systems operating at the same time. That state would call for more power than the probe had, so the fault protection kicked in to turn off non-essential systems.
NASA’s Jet Propulsion Laboratory (JPL) equipped Voyager 2 with a radioisotope thermoelectric generator (RTG) for power as it’s too far from the sun for solar panels to be effective. This type of power source, the same used on the Curiosity Mars rover, provides a constant supply of power, but its potency drops a bit every year as the plutonium fuel decays. Engineers have slowly ratcheted down the probe’s power requirements over the years. For example, they disabled the heater on the cosmic ray subsystem instrument to save power. That instrument has continued to operate, though.
With a full understanding of the issue, JPL staff were able to reactivate the science suite yesterday (January 28th) by flipping off one of the high-power subsystems. The team is currently working to restore normal operations, but that will take some time. This is a machine from the 1970s after all, and it’s 11.5 billion miles away. Each command takes 17 hours to reach Voyager 2, and the confirmation takes 17 hours to come back. So, that’s almost a day and a half just to find out if a command did what it was supposed to do. Despite the difficulties, the Voyager probes remain vital tools in our study of deep space.
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