Juice Mission and the Sky-high Stakes of RIME Deployment

Category Space

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ESA’s Juice mission to Jupiter experienced a setback when the RIME antenna failed to deploy a few days after launch. The engineers had to figure out the fault and rectify it in order to move forward, as the mission to investigate the Jupiter system and its family of icy moons depended on its success.

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When the RIME antenna on ESA’s Juice mission failed to deploy a few days after launch, the engineering teams faced the mighty challenge to understand the fault and rectify it. At stake was a chance to see inside Jupiter’s mysterious icy moons.

The stakes were already high before the spacecraft ever left the ground. ESA’s Jupiter Icy Moons Explorer (Juice) was designed by Airbus to conduct an unprecedented investigation of the Jupiter system and its family of icy moons.

The Juice mission was launched on April 14th, 2023 to Jupiter.

A key to that investigation is the Radar for Icy Moon Exploration (RIME) antenna, which is part of Juice’s comprehensive suite of ten science instruments. Once in the Jupiter system, RIME will be used to remotely probe the subsurface of Jupiter’s icy moons. Its radar signals will penetrate the moons to a depth of 9 km, and reveal details of between 50 and 140 m across. This will give insight into their geology and provide unique data to understand the habitability of these remote, icy moons.

The RIME antenna was built with eight segments, three of which are deployable, the other five are fixed.

But to succeed in collecting this data, scientists had to first get the spacecraft and its instruments into space – and that meant folding up some of the hardware.

At 16 m in length, the RIME antenna was too long to fit inside the nose cone of the Ariane 5 rocket that launched Juice into space. It was therefore constructed in two booms of four segments each. Of those eight segments, three would deploy on one side of the spacecraft, three on the other side, and two would remain fixed on the spacecraft. For launch, the three deployable segments were folded back onto the fixed segment and held in place by two brackets.

The Juice mission was designed to last 7.5 years, passing through Jupiter's magnetosphere and studying Ganymede, Europa and Callisto.

Once in space, devices called non-explosive actuators (NEAs) would be remotely activated one after the other from the European Space Operations Centre (ESOC), Darmstadt, Germany. Each NEA would remove a holding pin from its bracket, allowing that section to spring into place.

And that’s where the problems began.

Ronan Le Letty, Senior Mechanisms Engineer for ESA and part of the Juice team, was at ESOC during the RIME deployment, advising the flight control team who were receiving telemetry from the spacecraft’s various onboard sensors and sending Juice commands.

The two monitoring cameras that tracked the RIME deployment were mounted onboard the spacecraft.

The procedure began on April 17, 2023, three days after the launch and with everything having proceeded smoothly up until that point.

Continuing this trend, the first step went without a hitch. Two monitoring cameras, mounted onboard the spacecraft, were used to follow the RIME deployment. From the downloads, the antenna segment was visible on one image, and then not on the next. In between the images, the NEA had fired, the pin had released and the antenna segment had snapped into place. A check of the external camera’s image showed the segment in place, and the telemetry data also confirmed this. It showed that the spacecraft was oscillating as expected from the sudden deployment of the boom, and that the Attitude and Orbit Control System (AOCS) was correcting for the last of these movements.

The AOCS of Juice spacecraft corrects the attitude and orbit of the spacecraft, allowing it to maintain its trajectory and course.

Satisfied, the team moved on to the second segment.

The command was given to fire the actuator. The telemetry arrived before the images, but something was wrong. The expected oscillation was naught to be seen, and the AOCS had no corrections to make.

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