Uncertainty and disturbance-observer based robust attitude control for satellites

An Adaptive Control Methodology for Spacecraft Attitude Tracking Under Model and Environmental Uncertainties

“…The first theorem states that the gain has an upper bound if the magnitude of the control torque is limited (because any physical actuators cannot generate infinite torques). The second theorem guarantees the finite-time boundedness of the uncertain attitude dynamic system controlled by the robust adaptive control algorithm proposed in (36) and (38).…”

“…with a proper design of the compensating controller r Γ . For low-Earth satellites or spacecraft, the vector   t δ is mainly caused by solar array deployment, aerodynamic torque, magnetic torque, solar radiation torque, and gravity-gradient torque, and it is known that these disturbance values are bounded [35], [36].…”

“…It is noted that mass matrix q M is the nominal one, which is known. Although the form of the control law (36) is similar to the one proposed in [30], it was assumed in [30] that the upper bound on the uncertainty is a priori known and so a constant gain was used. On the contrary, in this paper the control gain   K t is updated by the following adaptation rule:…”

“…The first controller given in ( 27) is automatically determined once we select A and b to satisfy a prescribed performance. In designing the second controller given in (36), six parameters (  ,  ,  ,  ,  ,  ) are to be selected. The influence of each parameter on the performance is as follows:…”

“…The parameter  in (38) determines when to increase or decrease the gain. It is obvious from (38)   is selected in (36), then the controller (36) becomes a simple PD controller with the adaptive gain so that…”