ESA GNC Conference Papers Repository
Design of a vision-based navigation camera for JUICE
The Jupiter Icy Moon Explorer (JUICE) is an ESA mission whose aim is to study the Jovian system; Jupiter itself, its moons (Europa, Ganymede and Callisto) and the magnetosphere. The mission profile imposes considerable radiation constraints on the spacecraft, which are uncommon in typical space programs due to the Jupiter magnetic moment which is the largest of the solar system (almost 20 000 times more than the Earth). It results in a high total dose exposure at electronic parts level (factor ten with regards to typical GEO missions), high number of Single Event Effects and internal charging effects. For this challenging mission, the European Space Agency (ESA) has selected Sodern in association with ADS Toulouse, as an experienced team in Star trackers, Cameras and navigation systems, to preliminary design an optimized camera, taking into account the synergy with current star tracker available technologies and the specific Jovian harsh environment already extensively analyzed in another precursor activity (under ESA contract) dedicated to Star tracker enhanced robustness for the same JUICE mission. The HAS2 detector flying onboard HYDRA star trackers and already deeply characterized under Jovian electron fluxes in another precursor activity (under ESA contract) is identified as the best TRL9 candidate for the Navigation Camera also.Camera main features outcomes from trade-off applied during this study are as follows: - Reuse of HAS2 detector already extensively characterized under Jupiter harsh environment, - 5° Field of View (FoV) necessary as a minimum, with an helpful enhanced performance for moon detection in 4° FoV configuration, - 80mm pupil diameter for star detection still efficient on worst case of the vault during harsh Jupiter electrons fluxes (including x4 margin), - 28° SEA Baffle that enables most observation slots for a reasonable mass and volume. Camera performances and navigation output features were consolidated by an HFS (High Fidelity Simulator) model able to incorporate high electron fluxes hits on the detector during the Jupiter tour. This study permitted to clearly identify driving parameters of Navigation performance; in view of camera consolidated requirements, and then efficient sizing accordingly. The key elements that allow the Navigation Camera to withstand the Jovian specific worst case environment are an optimized Field of View (FoV) between low value for highest resolution on moons and extended value for easier star detection probability, a well sized optical design able to collect a sufficient signal to noise ratio for stars with minimized moon stray light or unwanted ghost images, the detection algorithms efficiency, and obviously the additional shielding around the detector to be optimized within the camera overall mass budget. This activity took place within a period of 24 months from 07/2014 to 07/2016, with a 4° Field of View proposed design able to meet the performances.