Reentry vehicle modeling and sliding mode controller design

A Six Degrees of Freedom(Six-DoF) reentry vehicle model is being developed for control studies. This vehicle model is highly nonlinear, multivariable, unstable and coupling and includes uncertain parameters. The dynamic inverse method and sliding mode control are used in inner-loop and outer-loop for the reentry vehicle control respectively according to the dynamic equations. When dynamic inversion decoupling technology is applied to the vehicle model, the output dynamics for pitch angle, yaw angle and rolling angle can be derived by differentiating two times respectively. The relative degree equals to the rotational motion system order. Thus, rotational motion dynamic model can be Input/Output linearized completely and is decoupled. A multi-input/multi-output(MIMO) sliding mode controller is designed based on the linearized model. Saturation function is applied to reduce the chattering of the slide mode. Simulation studies are conducted for initial conditions of altitude of 60km and Mach 20 for the responses of the commands of angle of attack, sideslip angle and bank angle. The simulation studies demonstrate that the proposed controller is robust with respect to the interference and parametric uncertainties, and meets the performance requirements with acceptable control inputs.