Distributed network of smart actuators/sensors for active micro-vibration control in large space antenna structures

One of the major needs of future Earth Observation satellites is to fulfil high demanding pointing requirements when using instrumentation supported by or mounted at the end of very large flexible truss structures. Those spacecraft often call for the capacity of performing fast and precise manoeuvres without losing strict control over flexible parts. In this context, avoiding geometric distortions in images or issues affecting the accuracy of communications is a critical objective to be achieved in the near future. In addition, on-board mechanical disturbances can be generated by frequently used devices as attitude control equipment and pointing mechanisms. In this perspective, a network of smart actuators/sensors can be mounted on a passive structure to make it able to counteract undesired elastic vibrations. In this paper, the problem of micro-vibration control for an in-orbit spacecraft equipped with a very large flexible antenna is addressed. The instrument is sustained by an active frame hosting an optimally distributed network of actuators and sensors dedicated to vibrations suppression. The fully coupled 3-D equations for an in-orbit flexible spacecraft subjected to gravitational forces and orbit disturbances are derived taking into account the presence of the smart materials. The 3-D flexible structure model is developed and validated via FEM formulation by using commercial codes. The model is then reduced to obtain a system to be easily handled by control systems algorithms. A placement strategy to identify the best location for vibration control devices is carried out by using Gramian-based techniques. Typical profiles of attitude manoeuvres are then simulated by applying a torque generated either from reaction thrusters or motors connected to reaction wheels while simultaneously suppressing unwanted vibrations. To achieve high performance, feedback methods are implemented to coordinate the simultaneous action of actuators devices and ensure structural accuracy and pointing requirements are satisfied during operations.