The 45-year-old Voyager 1 deep space probe is showing its age as NASA engineers try to determine why it is sending back invalid telemetry data from its attitude control system as it hurtles through interstellar space, never to return.

Launched in 1977, Voyager 1 is currently 14.5 billion miles (23.3 billion km) from Earth – a distance so great that a radio signal takes 20 hours and 33 minutes to reach it from Mission Control. Despite nearly half a century of service during which the robotic spacecraft visited Jupiter in 1979, followed by Saturn and its giant moon Titan in 1980, Voyager 1 is still functioning and sending back science instrument data.

It manages this thanks to its three plutonium-fueled Radioisotope Thermoelectric Generators (RTGs) that are expected to continue to provide the probe with power until sometime after 2025. However, Voyager 1 and its sister craft Voyager 2 have been reconfigured occasionally to overcome power dips and malfunctions, and to make sure they continue doing useful work until the RTGs fail.

In addition, Voyager 1 has been bombarded by cosmic radiation for decades and this is taking its toll on its electronics, which is one reason why NASA engineers monitor the craft’s systems so closely.

The present difficulty is with the attitude articulation and control system (AACS). Though Voyager 1 is receiving and executing commands from Earth, and is sending back data from its science instruments, the AACS, which helps to keep the probe’s high-gain antenna pointed at Earth, is returning data that seems to be random or doesn’t match any state that the AACS could ever be in.

According to NASA, the malfunction wasn’t serious enough to trigger the onboard fault protection systems and the signal isn’t losing strength, showing that the high-gain antenna is still pointing in the right direction. The team is seeking to locate the source of the problem and whether it involves any other spacecraft systems. If the source cannot be found, the alternative may be to switch to a redundant hardware system.

“A mystery like this is sort of par for the course at this stage of the Voyager mission,” said Suzanne Dodd, project manager for Voyager 1 and 2 at NASA’s Jet Propulsion Laboratory in Pasadena, California. “The spacecraft are both almost 45 years old, which is far beyond what the mission planners anticipated. We’re also in interstellar space – a high-radiation environment that no spacecraft have flown in before. So there are some big challenges for the engineering team. But I think if there’s a way to solve this issue with the AACS, our team will find it.”

Source: NASA