Optimal control study for the Space Station solar dynamic power module

The authors present the design of an optimal control system for the Space Station Freedom solar dynamic fine pointing and tracking (SDFPT) module. A very large state model of six rigid modes and 272 flexible modes is used in conjunction with classical LQG optimal control to produce a full-order controller which satisfies the requirements. The results obtained are compared with those of a classically designed PID (proportional plus integral plus derivative) controller that was implemented for a six-rigid-body-mode forty-flexible-mode model. A major difficulty with designing LQG controllers for large models is solving the Ricati equation that arises from the optimal formulation. A Riccati solver based on a Pade approximation to the matrix sign function is used. A symmetric version of this algorithm is derived for the special class of Hamiltonian matrices, thereby yielding, for large problems, a nearly twofold speed increase over a previous algorithm