ESA GNC Conference Papers Repository
The Euclid AOCS tasks at system level
Thales Alenia Space Italy is prime contractor of the Euclid Medium Class mission that belonging to the ESA 2015-2025 Cosmic Vision plan that is currently in the C/D phase. Euclid will be launched in 2020 and will operate for more than 6 years in large amplitude orbit around L2. The scientific objective of Euclid is to understand the origin of the Universe's accelerating expansion, by mapping large-scale structure over a cosmic time covering the last 10 billion years. To investigate the nature of dark energy, dark matter and gravity, the mission will target two independent primary cosmological probes: Weak gravitational Lensing and Baryonic Acoustic Oscillations. Both probes require the ability to survey a large fraction of the extra-galactic sky over the mission lifetime, with very high system stability (telescope, focal plane, spacecraft pointing) to minimise systematic effects. The program is organized allocating all Sub-Systems to different European industries, and in particular, Sener and ADSNL are in charge of the AOCS design and implementation. Nevertheless, significant technical AOCS tasks, in addition to the typical System level activities, are performed by the Prime. The extremely accurate pointing performance is achieved through the use of the Fine Guidance Sensor. The FGS is specified and procured by the Prime from Leonardo Firenze and in cooperation with Astronomic Observatory of Turin (OATo) for the provision of reference source catalogue derived from the GAIA data release. Key elements related to FGS are the support to the on-ground verification through the development by the Prime of high fidelity and real-time mathematical model, and the definition of the incremental approach to be used in-flight for calibrating the FGS. Hybrid solution is implemented for the actuators (reaction wheels and cold-gas micropropulsion system) used in the scientific mode. This solution defined at System level has required execution of RWL's characterization test for the start-stop approach, as well as refined modeling of the MPS system. The efficiency of the scientific mission is significantly improved thanks to the implementation of dedicated mechanism (CMU) used to compensate the angular momentum produced by moving parts of the telescope like Grism and Filter Wheels. Different solutions have been traded and the CMU is implemented as fifth RWL handled by the AOCS used in start-stop regime. The selection of the control approach and the implementation of the algorithm for commanding the Antenna Pointing Mechanism has been kept at System level, relying as much as possible on the quite sophisticated functions implemented in its electronics (ADPME). The paper will present general view of the AOCS architecture with particular focus on the contributions provided by the tasks performed at System level, leaving to other papers presented by the AOCS developers addressing specific aspects like the control approach for achieving the scientific performance and the FDIR logic.