  The paper develops a Model Predictive Controller for constrained control of
spacecraft attitude with reaction wheel actuators. The controller exploits a
special formulation of the cost with the reference governor like term, a low
complexity addition of integral action to guarantee offset-free tracking of
attitude set points, and an online optimization algorithm for the solution of
the Quadratic Programming problem which is tailored to run in fixed-point
arithmetic. Simulations on a nonlinear spacecraft model demonstrate that the
MPC controller achieves good tracking performance while satisfying reaction
wheel torque constraints. The controller also has low computational complexity
and is suitable for implementation in spacecrafts with fixed-point processors.
