Adaptive Attitude Control of a Dual-Rigid-Body Spacecraft with Unmodeled Nonminimum-Phase Dynamics

We consider control of a dual rigid-body space-craft consisting of a bus and an appendage connected by a compliant joint. Thrust actuators are located on the spacecraft bus, and performance measurements are obtained from sensors on the appendage. This problem is challenging due to the flexibility of the joint and the noncolocation between the actuation and the performance variable. The goal is to motivate and investigate the challenges arising in control of nonminimum-phase (NMP) systems with rigid- and flexible-body dynamics. Exact equations of motion are derived for the spacecraft, and the invariant zeros of the linearized model are determined. This paper investigates the robustness of an adaptive control law to variations in the mass and inertia matrices of the bus and appendage as well as the geometry and joint stiffness. The adaptive controller uses no knowledge of the NMP dynamics.