A drag free control based on model predictive techniques

This paper presents a solution for the drag free control problem of the European satellite GOCE based on model predictive techniques. The approach followed during the orbit and attitude modelling yields to the decoupling of the plant's six degrees of freedom into four linearized systems that include satellite's dynamics, sensors and its corresponding noise profiles, actuators and its relative noise profiles and also, the characterization of the main exogenous disturbances (drag forces and torques). In the problem formulation are considered performance constrains in terms of the propulsion system activity, residual acceleration levels (linear and angular) and the spacecraft's attitude angles. Also, it is presented the process to traduce the orbit and attitude performance requirements into specific mathematical constraints for the calculation of the optimal control law by means of predictive techniques. 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 fulfilment of constraints and the performance requirements achieving.