Model reference adaptive control of a small satellite in the presence of parameter uncertainties

Abstract

An accurate control algorithm for small satellites is critical to mission success. In this paper, a novel discrete-time Model Reference Adaptive Control (MRAC) algorithm is developed based on a unified approach for the attitude control of a three-axis stabilized nonlinear satellite model. The linearized model of a satellite with unknown dynamic parameters is derived and a Recursive Least Squares (RLS) algorithm is used to identify the linear model's unknown parameters. In order to take into account the nonlinear model of satellite dynamics, the proposed MRAC strategy is used considering the linear model, the estimation error; and the difference between the actual nonlinear system and the linear model outputs. The actual nonlinear model of the satellite includes moments of inertia uncertainties, external disturbances, and sensor noise on the outputs. The introduced controller performance is compared with a conventional discrete -time MRAC which demonstrates excellent simultaneous regulation and tracking capabilities.