SYNTHESIS AND SURVEY OF CONTROL LAWS FOR LARGE FLEXIBLE SPACECRAFT

Stabilization and performance of the dynamics of most modern spacecraft is to be achieved by the introduction of onboard automatic control, in­ volving a careful choice of sensors, actuators and control algorithms embedded in one or more onboard computers. Complications arise when structural deformation in the spacecraft must be taken into account. This is the case with several current as well as future space­ craft, which display unusual geometries and large dimensions, and which are re­ quired to satisfy rigorous performance requirements. The control of such spacecraft, displaying non-negligible interaction between control and structural de­ formation, is the subject of this presentation. The earliest experiences with performance degradation due to control/struc ­ ture interaction are recalled. The interaction problem is schematized in terms of spill-over between design model and residual model of the spacecraft dynamics. Robust control for spacecraft stabilization is described, as well as control for space­ craft performance. The latter may induce instability, and therefore, robustness en­ hancement is called for. Various alternative approaches are outlined. Modifications of mechanical system properties as well as of control algorithms will be with the designer well into the spacecraft's active life. Therefore, continued end-to-end simulations involving updated truth models and updated control algo­ rithms are required for continued and successful confrontation with physical real­ ity.