CONTROL OF SPACE PLATFORMS WITH FLEXIBLE LINKS USING COMMAND SHAPING METHOD

The rapid growth of space utilization requires construction and maintenance of space structures and satellites in orbit that, in turn, substantiate the application of robotic systems in space. In this paper, a near-minimum-time optimal control law is developed for a rigid space platform with flexible links such as manipulators, solar panels and stabilizing booms during an orientating maneuver with a large angle of rotation. The time optimal control solution for the rigid-body mode is obtained as a bang-bang function and applied to the flexible system after smoothing the control inputs to avoid stimulation of the flexible modes. This will also reflect practical limitations in exerting bang-bang actuator forces/torques, due to delays and non-zero time constants of existing actuation elements. The smoothness of the input command is obtained by reshaping its profile based on consideration of additional derivative constraints. The platform is modeled as a linear undamped elastic system that yields an appropriate model for the analysis of planar rotational maneuvers. The developed control law is applied on a given satellite during a slewing maneuver, and the simulation results show that the modified realistic optimal input compared to the bang-bang solution goes well with the practical limitations and also alleviates the vibrating motion of the flexible appendage, which reveals the merits of the new developed control law.