Experimental validation of agile attitude control with sinc function-based profiler for reducing residual vibrations

This paper presents a tracking control system combining feedforward and feedback with shaped input, using a benchmark problem applied to a two-mode system. Simulations and experimental validation of the new control system for tracking control of flexible spacecraft including comparison with conventional methods are presented. The results show that the residual vibrations after the moves by the proposed control system are smaller than the conventional methods in the presence of an unknown high-order flexible mode. Sinc function-based command shaping where the spacecraft attitude is controlled along a sequentially commanded trajectory and the residual vibration after the move can be significantly reduced. Sinc function is known as an extra-insensitive function which has no frequency response above a certain threshold frequency. Three feedback controllers are applied to the control system and compared using the benchmark problem. This controller design has several unique characteristics. First, the sinc function-based shaped input is designed to reduce residual vibrations after maneuvers under the existence of unknown high-order mode. Conventional input shapers for flexible spacecraft are not effective for multi-mode system with unknown flexible modes, where actual flexible spacecraft usually has such unknown high-order flexible modes. Second, only the dynamics of the low-order mode need to be considered in designing all the feedforward, feedback controller, and shaped input. Experimental validation is performed by hardware-in-the-loop (HIL) test configuration with newly developed real-time onboard computer to evaluate the feasibility of processing load by the proposed algorithms for real-time processing. Because the proposed algorithms do not contain any iteration algorithm, the proposed algorithms can be implemented in actual satellites with feasible processing load. The assumed two-mode system represents the most simplified multi-mode system with unknown high-order mode, so the similar results can be expected for systems equipped with more complicated flexible structures.