Control of underactuated spacecraft by dynamic implementation of a sequence of feasible rotations

A control law for attitude control of an underactuated spacecraft is proposed and tested in simulation. A cluster of two reaction wheels (RWs) is assumed, which represents a possible scenario after failure of one RW in a non-redundant 3 wheel cluster, or multiple failures, when more than 3 RWs are installed. When only two attitude actuators are available, the spacecraft is no longer fully controllable and stabilizable by means of a continuous static feedback. Nonlinear Model Predictive Control is investigated as a possible approach for the derivation of a suitable control system, which allows for full three-axis control, in spite of underactuation, with acceptable closed-loop performance, in the presence of torque saturation, uncertainties and external perturbations. Convergence is analyzed for several large angle slews, in order to demonstrate the viability of the approach.