Orbit and attitude control for the European satellite GOCE

This paper presents simultaneous solution of the orbit and attitude control for a low earth orbiter of the European Space Agency that will develop a high accurate measurement of the Earth´s gravity field (less than 10 μ/s²) and the geoid modelling (accuracy of 1 - 2 cm) at a spatial resolution better than 100 km. In order to satisfy the stringent performance requirements of the mission (drag compensation down μN and attitude tracking with μrad accuracy) with reasonable control robustness, a H_∞ technique based on a linear matrix inequalities optimization procedure is implemented. The approach followed during the orbit and attitude modelling which leads to the decoupling of the plant´s dynamic into four systems that include a description of the satellite´s linear and rotational behavior, the mission sensors and actuators with their respective noise model. A detailed frequency characterization of the main exogenous disturbances (drag forces and torques) is developed through a comparative study employing parametric, non-parametric and subspace methods. Simulation results using atmospheric drag profiles validated for this mission by Alenia Spazio (main mission contractor) are presented and analyzed in order to confirm the fulfillment of the constraints and the performance requirements.