  The paper addresses a problem of constrained spacecraft attitude
stabilization with simultaneous reaction wheel (RW) desaturation. The
spacecraft has a reaction wheel array (RWA) consisting of four RWs in a
pyramidal configuration. The developments exploit a spacecraft dynamics model
with gravity gradient torques. The linearized dynamics are shown to be
controllable at almost all RWA configurations. Configurations that result in
the highest Degree of Controllability are elucidated. A strategy that combines
an incremental reference governor and time-distributed model predictive control
is proposed to perform constrained RW desaturation at low computational cost.
Simulation results of successful RW desaturation maneuvers subject to
spacecraft pointing constraints, RW zero-speed crossing avoidance and limits on
control moments are reported.
