ESA GNC Conference Papers Repository
AOCS & image navigation and registration for earth observation from GEO
This paper presents the results from a study on the co-design of Attitude and Orbit Control System (AOCS) and Image Navigation and Registration (INR) as applied to a high resolution geostationary observation mission (Geo-HR) to be deployed in the 2025-2030 timeframe. To enable maritime surveillance and disaster management, the mission combines the need for a high resolution imaging satellite with high responsiveness and high revisit capabilities, which impose significant manoeuvring capabilities as well as high pointing accuracy and stability. The work described here focuses on the selection process for the AOCS & INR coupling architectures, on the AOCS & INR subsystems design, and on the performance assessment aspects - through Monte Carlo simulations of the field-of-view (FOV) stabilization and image acquisition phases of the Geo-HR mission. Two AOCS & INR architectures are proposed and investigated. In the first solution (a so-called Class 1 architecture) the on-board AOCS receives regular ground updates from the INR, which uses image processing algorithms based on landmark detection and matching and absolute geo-location information from Ground Control Points (GCP) to correct for LF navigation and pointing errors. In the second solution (class 2 architecture), a new high accuracy star tracker along with an on-board image based sensor are introduced in-the-loop to improve the on-board attitude knowledge of the vehicle. A functional model has been developed for the new on-board image based sensor, which estimates relative translation between consecutive images with sub-pixel accuracy. The sensor is able to track prominent features in image sequences with on-board image processing algorithms based on template matching. A dedicated simulation tool for Earth Observation missions, EOSIM, is described. EOSIM is used to simulate a closed loop of the AOCS & INR systems, including a detailed image acquisition and generation function. The pointing and stability performance of the proposed solutions are derived from statistical analysis of the results from Monte Carlo simulation campaigns, performed in representative Geo-HR missions scenarios of maritime surveillance and disaster management. The robustness of the AOCS & INR systems to poor illumination conditions was also assessed for a low luminance maritime test case. Test Results show that the proposed scenarios fulfil the stringent pointing & stability requirements of the Geo-HR mission. The gain in pointing & stability performance with respect to current Earth Observation missions is demonstrated, as well as the impact of using absolute geo-location measurements and visual information in the estimation of spacecraft attitude.