JUICE Attitude and Orbit Control System : major HW & SW challenges from design to development & validation
Authors:   Airbus Defence And Space, Toulouse, France, Regnier Pascal , Llamas Jeremy , Grzymisch Jonathan 
Published: January 2024

The JUICE - JUpiter ICy moons Explorer – mission is the first large-class mission in ESA's Cosmic Vision 2015-2025 programme. Planned for launch in 2023 and arrival at Jupiter in 2031, it will spend at least three years making detailed observations of the giant gaseous planet Jupiter and three of its largest moons, Ganymede, Callisto and Europa, through more than 25 fly-bys and a final orbiting phase around Ganymede. Airbus Defence and Space Toulouse was selected as Prime Contractor in July 2015, and is responsible for the design and development of the AOCS Subsystem and the on-board Software. This paper focuses on the post CDR status of the JUICE AOCS HW and SW development and validation. Since the last JUICE presentation at the ESA GNC conference in 2017, AOCS equipment suppliers and Airbus, together with ESA, have made all efforts to progress on the development and qualification of AOCS HW and SW that best meet the demanding JUICE mission objectives and requirements. The major challenges encountered during this phase, and the solutions implemented by ADS and its partners, were in particular :

•AOCS equipment enhancement of robustness to the jovian harsh radiation environment, and fulfillment of specific performance and autonomy needs of the JUICE mission : especially for the Star Tracker, the Inertial Measurement Unit, the Reaction Wheel and the Navigation Camera

•Unique challenges posed on AOCS by a large Spacecraft with multiple flexible appendages, large propellant tanks and a main engine to be fired with large deployed solar arrays : main engine manoeuvres shaping, active damping loop of solar panels Out-Of-Plane flexible mode in safe mode, thrusters actuation frequency spreading. All these AOCS innovative solutions were successfully implemented and qualified through an intensive Monte-Carlo simulation campaign and functional testing with HW in-the-loop. In addition, coupled AOCS / CFD simulations have been performed in order to rule out any potential coupling issue between solar arrays flexible modes and liquid sloshing modes during critical mission phases neither in 0g nor in 1g conditions (namely the Emergency Damping Loop control in safe mode following a main engine thrust interruption).

•Specific JUICE mission needs in navigation and science pointing accuracy, calling for vision-based autonomous navigation during jovian moons flybys, implemented through the EAGLE (for Enhanced Autonomous Guidance through Limb Extraction) on-board SW application. At the start of the prime contract with Airbus, EAGLE was a nice-to-have innovative concept still to be consolidated and promoted to convince mission authorities at ESA that it could really contribute to improve science return, and that it could be qualified for flight. Now a few years later, EAGLE is called by the ESOC CREMA, and EAGLE SW development and validation has been validated through closed-loop AOCS / Navigation performance simulations with Surrender virtual scene generation tool in-the-loop, as well as functional testing with HW in-the-loop. Even further, ESA has asked Airbus to complement EAGLE SW with an on-board estimation of the fly-by closest approach time-of-flight in order to better synchronize science payload instruments operations with the S/C relative trajectory. Available EAGLE validation results will be presented at the conference.

•Specific JUICE mission needs in autonomy, calling for enhanced robustness to potential STR outages and autonomous resumption of critical insertion manoeuvres after safe mode : several specific SW functions have been developed to not only improve the AOCS robustness to STR outages which could result from the jovian harsh radiative environment, but also to minimize the probability of such STR outages, by assisting the STR for fast tracking recovery after a potential loss of tracking. Furthermore a major change in the overall JUICE FDIR strategy during mission-critical fail-operational phases was to replace an avionics warm-restart concept by a resume-after-safe-mode concept, proving more efficient to implement and validate. The final status of these enhanced-autonomy functions will be presented at the conference.

•Non recurrent AOCS Software generation with Autocoding in a demanding ESA science SW product assurance environment : a lot of efforts have been spent to align the Airbus autocoding process with ESA SW PA expectations in a very constrained programmatic environment

In addition to the above topics, if possible first results from orbit will be presented.