| Future large spacecraft referred to as Large Space Structures will be characterized by structural flexibility and the potential for the interaction of structural deformations with the rigid body control system. Furthermore, the control task may include active control requirements, e.g., vibration suppression. Due to limitations of flight computers, the control model may be of lower order than the number of dynamically significant states. Application of multivariable LQG theory to design reduced-order compensators leads to the presence of control spillover and observation spillover interacting through the residual (unmodeled) modes. Such control designs fundamentally lack robustness.;In this dissertation, the development of compensators for large space structures is posed as a problem in robust control system design. Toward the solution of this problem, a methodology is developed for the design of compensators which shape the system loop gain singular values. The frequency-shaped control and estimation theory of Gupta, as reformulated by Kim for measurement frequency-shaping, has been extended to include frequency-shaping of the control law. It is shown that zeroes of the control law shaping filter become transmission zeroes of the compensator, and this result completes the duality of the frequency-shaped regulator and estimator.;To design control systems with desired loop gain characteristics, a recursive eigenstructure assignment procedure has been developed. By use of this algorithm, optimal regulators and estimators with assigned eigenvalues can be designed. With a modification of the usual regulator-estimator design method, the compensator can be designed with specific eigenvalues. When frequency-shaping is incorporated into the compensator, this eigenvalue assignment feature allows the compensator to retain both the poles and the zeroes of the shaping filter. Eigenstructure assignment of the compensator specifically shapes the loop gains and can be used for robustness enhancement. This capability has been demonstrated for several control systems, including one for a large space structure. |
