| This dissertation develops a theoretical and practical framework for solving problems of optimal structural design and optimal control in an integrated fashion. This formalism calls for optimization of control objective functions with respect to control and structural design variables; it is applied to time optimal maneuvers of flexible spacecraft. Issues related to the problem formulation, analysis and development of the problem solving procedures, and computational feasibility have been emphasized. The maneuverability index, defined to reflect the time required to perform a rest-to-rest attitude maneuver for a set of given angles, is the primary design objective. The performance degradation of the system, defined to reflect the attitude error after a maneuver, is the secondary objective. We have investigated the performance degradation coming from the uncontrolled dynamics of the structure and from the effect of faults. The performance degradation from the uncontrolled dynamics has been taken into account by the design constraint that the post-maneuver spillover be within a specified bound. In order to account for the performance degradation from the effect of faults, fault tolerance of the system has been considered as a part of the design problem, leading to a multicriterion design problem. The fault tolerant design is to minimize the worst performance degradation from all admissible faults by adjusting the structural design variables of the spacecraft. Adaptive approximate design methods have been developed to overcome the computational difficulties. Numerical examples suggest that optimization of design can provide significant improvement of maneuverability and that it is possible to improve the fault tolerance substantially as well with relatively little loss in the primary objective. |
