An analytical approach is developed for determining the spacecraft attitude response to disturbances caused by the stick-slip motion of a large extended structure with a tension control mechanism. In this method, attitude dynamics with a flexible appendage is formulated as a general constrained mode model, and coupling with the stick-slip motion is formulated as the transition of equilibrium states of modal parameters. Numerical calculations are presented for the flexible solar array on the Advanced Earth Observing Satellite. This satellite experienced unexpected attitude oscillations due to the stick-slip motion while operating in orbit.