The ESA’s JUpiter Icy Moons Explorer (JUICE) is on its way to conduct detailed studies of Jupiter and its three icy moons, Ganymede, Callisto, and Europa. To pick up speed and reach Jupiter by July 2031, the probe will conduct a gravity-assist maneuver with Venus on Sunday, August 31st. According to the ESA, the mission suffered an anomaly with its communications system, which temporarily severed its connection with Earth. Fortunately, a coordinated response by teams at the ESA’s European Space Operations Centre (ESOC) and Airbus (JUICE’s manufacturer) restored communications in time for the probe’s flyby.
The anomaly occurred when a ground-based antenna in the ESA’s Deep Space Network failed to establish contact on July 16th. A quick diagnostic determined that the issue was not with the ground station, leading the JUICE team at ESOC to fear that multiple systems had failed, prompting the probe to enter survival mode. When this happens, the spacecraft starts to spin and its antenna (which will sweep across Earth once an hour) to transmit an intermittent signal. Since no signal was detected, the two teams began looking into the communications subsystem for indications of problems or misalignment.
As Angela Dietz, Juice Spacecraft Operations Manager, explained in an ESA press release:
Losing contact with a spacecraft is one of the most serious scenarios we can face. With no telemetry, it is much more difficult to diagnose and resolve the root cause of an issue. Waiting was not an option. We had to act fast. Waiting two weeks for the reset would have meant delaying important preparations for the Venus flyby.
To resolve the issue, the team could wait for the next automatic reset, which was fourteen days away. Alternately, they could try blind messaging – sending commands in the direction of JUICE and hope they were received by one of its backup low-gain antennas. This latter approach posed a challenge since JUICE was about 200 million km (125.25 million mi) from Earth and on the other side of the Sun at the time, which imposes a communications lag of 22 minutes to send and receive a signal. Recovery attempts lasted almost 20 hours straight, with the teams working through the night, and they eventually got a response.
The blind commands activated the spacecraft’s signal amplifier (which boosts JUICE’s signals), and contact was re-established. The teams found that JUICE was in perfect working conditions, that no systems had failed, and the spacecraft was still on track to make its flyby with Venus. They also determined that the anomaly was caused by a timing issue with the software that switches the signal amplifier on and off. Said Dietz:
It was a subtle bug, but one that we were prepared to investigate and resolve. 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. This was a textbook example of teamwork under pressure. Thanks to the team’s calm and methodical approach, we were able to recover Juice without any lasting impact on the mission.
Timeline of JUICE’s journey to Jupiter and its moons. Credit: ESA
JUICE will make its closest approach to Venus at 07:28 CEST on Sunday, August 31st (01:28 EST; 10:28 PST, Aug. 30th), one of four planned gravity-assist maneuvers. The first occurred in August 2024 when JUICE made a flyby with the Earth-Moon system, and two more will occur with Earth in September 2026 and January 2029. These maneuvers are necessary since JUICE is one of the heaviest interplanetary spacecraft ever launched (6000 kg; 13230 lbs). The coming flybys will also adjust the probe’s trajectory so that it will rendezvous with Jupiter in July 2031.
Further Reading: JUICE