Nonlinear Robust Control and Observation for Aeroelastic Launch Vehicles with Propellant Slosh in a Turbulent Atmosphere

This paper focuses on the attitude control and propellant slosh suppression of aeroelastic launch vehicles in a turbulent atmosphere. For a five-degree pitch-angle block command, the tracking performance of the selected Incremental Non-Linear Dynamic Inversion Sliding Mode Controller (INDI-SMC) shows excellent tracking performance. However, turbulence still inevitably leads to oscillatory behaviour in the swivel command. Various filter designs have been implemented to improve the smoothness of INDI-SMC. Using either a notch or band-pass filter in the sensor-feedback loops of pitch angle and pitch rate only marginally reduced the swivel oscillations, but did not solve the problem for the rigid-body control. For the flexible launcher with slosh dynamics, filtering of the sensor-feedback signals reduced the oscillations in swivel command, and elastic and slosh motion significantly, but could not completely remove them. The preliminary design of a rigid-body state observer has been included, and the results show that the INDI-SMC controller remains stable in the presence of engine dynamics, sloshing, flexible modes, input errors due to the use of rigid-body and slosh-state observers, while flying in a turbulent wind field.