Command Filtered Modular Adaptive Backstepping Attitude Control of Spacecraft in Presence of Disturbance Torque

Attitude control of spacecraft is one of the most important issues in aerospace. Different control method for this purpose were proposed that each of these controllers have different behavior against disturbances. One of these methods is backstepping which is divided to adaptive and nonadaptive techniques. Since the spacecraft equations are nonlinear, linear control methods will not work in this case so the nonlinear control methods should be used. The modular adaptive backstepping method is a nonlinear adaptive control method and has a parameter update law that we can use different estimators to estimate system’s unknown parameters in this method. It is also possible to reduce the differentiation load of virtual control laws by using the command filtering method. In this paper, contrary to other works which mostly use discrete command filtering method, we use continuous command filtering method which the natural frequency and damping coefficient can be determined to bring down the computation of the time derivatives of virtual controls laws to differentiation. In this paper, after deriving spacecraft equations in terms of Modified Rodrigues Parameters, we design two stable attitude controllers for spacecraft using standard and command filtered modular adaptive backstepping methods and prove the stability of system using the Lyapunov theory and then simulation results of these controllers are compared with each other. Simulation results show good attitude tracking accuracy and success of adaptive backstepping method in having robustness against disturbance torque is proved