OPTIMAL ATTITUDE CONTROL THROUGH MAGNETIC TORQUERS AND REACTION WHEELS

An optimal attitude control method based upon linear quadratic regulator is applied to a spacecraft in an inclined orbit, alternatively using magnetic torquers and reaction wheels. The design objective of multi-axis pointing accuracy of 0.1 deg. with magnetic torquers, and 0.002 deg. with reaction wheels is demonstrated in the presence of environmental torques, without the need of a time varying control law design. The selection of optimal weighting matrices duly takes into account the underactuated and time varying nature of the plant with magnetic torquers. It is demonstrated that a well designed, constant feedback gain matrix precludes the necessity of sophisticated nonlinear and time varying design methods that require onboard programming.