Juice mission on track for Venus flyby after spacecraft communications restored

Juice mission on track for Venus flyby after spacecraft communications restored
by Clarence Oxford
Paris, France (SPX) Aug 25, 2025

The European Space Agency's Jupiter Icy Moons Explorer (Juice) has resumed normal operations after a communications anomaly temporarily cut contact during its cruise to Venus for a critical gravity-assist maneuver scheduled on 31 August.

The signal loss occurred on 16 July when Juice failed to establish contact with ESA's Cebreros ground station in Spain. Backup attempts from the New Norcia station also failed, confirming the issue was onboard. Engineers suspected a malfunction in the spacecraft's communications subsystem, possibly linked to its medium-gain antenna or transmitter.

ESA's mission team at the European Space Operations Centre (ESOC) in Germany, working with Airbus engineers, initiated blind commands from Earth to reorient and reconfigure the systems. With Juice positioned about 200 million km away and behind the Sun, every command took 11 minutes to arrive, followed by another 11 minutes to confirm success.

After 20 hours of continuous troubleshooting, a command succeeded in reactivating the signal amplifier, restoring contact and full telemetry. Engineers later traced the failure to a subtle software timing bug: an internal counter that resets every 16 months overlapped with the function controlling the amplifier, leaving the transmitter switched off.

"Losing contact with a spacecraft is one of the most serious scenarios we can face," said Angela Dietz, Juice Spacecraft Operations Manager. "Thanks to the team's calm and methodical approach, we were able to recover Juice without any lasting impact on the mission."

Juice is now preparing for its Venus flyby, during which the spacecraft will use its high-gain antenna as a shield against solar heat. Scientific instruments will remain offline for thermal protection, meaning no images of Venus will be taken. The maneuver is the second of four planned gravity assists designed to accelerate the nearly 6000 kg spacecraft to Jupiter.

A direct route would have required an 11 km/s departure speed, but Ariane 5 provided only 2.5 km/s at launch. By using flybys of Venus and Earth, Juice will steadily build up the required velocity. After passing Venus this week, the spacecraft will encounter Earth in 2026 and again in 2029, enabling its final trajectory toward arrival at Jupiter in July 2031.