ESA's Juice Spacecraft Overcomes Communication Glitch Ahead of Venus Flyby

The European Space Agency's Jupiter Icy Moons Explorer (Juice) is on course for its scheduled Venus flyby on August 31, following the successful resolution of a communication anomaly that temporarily severed contact with Earth.

The issue arose on July 16 during a routine ground station pass when ESA's deep space antenna in Cebreros, Spain, failed to establish contact with Juice at the expected time. Subsequent attempts via the New Norcia station also failed, confirming an onboard problem. Engineers suspected a misalignment of Juice's medium-gain antenna or a failure in the signal transmitter or amplifier.

"Losing contact with a spacecraft is one of the most serious scenarios we can face," said Angela Dietz, Juice Spacecraft Operations Manager. "With no telemetry, it is much more difficult to diagnose and resolve the root cause of an issue."

The recovery involved sending commands 'blind' into space, hoping they would be received by one of the backup low-gain antennas. After nearly 20 hours of troubleshooting, a command successfully activated the signal amplifier, restoring contact. The spacecraft was found to be in excellent condition, with all systems nominal.

The root cause was identified as a software timing bug. The function controlling the signal amplifier relies on an internal timer that restarts every 16 months. If the function accesses the timer precisely when it restarts, the amplifier remains off, rendering Juice's signal too weak to detect from Earth.

"It was a subtle bug, but one that we were prepared to investigate and resolve," said Dietz. "We have identified a number of possible ways to ensure that this does not happen again, and we are now deciding which solution would be the best to implement."

With the anomaly resolved, Juice is set to pass its closest point to Venus at 07:28 CEST on August 31, completing the second of four planned gravity assists. Designed for Jupiter's cold environment, Juice will use its high-gain antenna as a thermal shield to protect against Venus's intense solar heat. Due to thermal constraints, its remote sensing instruments will be inactive during the flyby, so no images of Venus will be captured.

Juice's mission includes multiple gravity-assist maneuvers to reach Jupiter. After the Venus flyby, it will perform Earth flybys in September 2026 and January 2029, aiming to arrive at Jupiter in July 2031. The mission will conduct detailed observations of Jupiter and its three large ocean-bearing moons: Ganymede, Callisto, and Europa.