Non-certainty-equivalent adaptive satellite attitude control using solar radiation pressure

Abstract

The article presents a new adaptive controller for attitude control of satellites using solar radiation pressure (SRP). The satellite has two identical solar flaps for pitch angle control. The model includes gravity gradient torque and the torque due to SRP. Unlike adaptive control design published in the literature for this model, here an adaptive law for large pitch angle trajectory control based on the non-certainty-equivalence principle is derived. The control system has a modular structure consisting of an estimator and a control module designed based on a backstepping method. Using Lyapunov analysis, it is shown that the closed-loop system is stable and the pitch angle trajectory asymptotically follows the reference trajectory. The control system designed here has some special features. In the closed-loop system, the trajectory is ultimately confined to a manifold in the space of state variables and parameter errors. Interestingly, once the estimated parameter values coincide with their true values during the adaptation process, these remain frozen and the estimation error remains zero thereafter, and the system recovers the performance of the deterministic controller. Simulation results are presented for a set of uncertain parameters of the model. These results show that in the closed-loop system, precise large pitch angle control is accomplished despite large uncertainties in the system parameters.