Spacecraft attitude tracking control under actuator magnitude deviation and misalignment

Adaptive backstepping control combined with a novel dynamic control allocation scheme is developed for attitude tracking control of a rigid spacecraft, in which multiple constraints are simultaneously considered, such as actuator uncertainties including torque magnitude deviation and misalignment, actuator constraints like saturation, external disturbances and even constrained energy consumption. More specifically, an adaptive backstepping control algorithm is firstly developed for the relative attitude tracking problem, in which the external disturbances and actuator uncertainties are explicitly considered, and Lyapunov stability analysis shows that asymptotical stability of the overall system is guaranteed. Moreover, to overcome the singularity or parameter drift caused by the parameter updating law, a switching parameter modification strategy is involved. In view of the above, a dynamic control allocation is further investigated to distribute the designed total control torques among the individual actuators. This method extends the conventional quadratic programming control allocation by penalizing the previous step before sampling intervals at a lower cost, and also the actuator magnitude and rate limitation are considered simultaneously by an auxiliary saturation function. Finally, a numerical simulation example for a rigid spacecraft is included to illustrate the feasibility and effectiveness of using the proposed scheme. (C) 2012 Elsevier Masson SAS. All rights reserved.