Integrated robust guidance and control of VTVL reusable launch vehicle at pre-landing phase using sliding mode control

In this article, guidance and control of the reusable launch vehicle at pre-landing phase have been studied. A plenty of vertical take-off and vertical landing (VTVL) reusable launch vehicle have been gradually developed to access the space allowing for reducing the flight operation costs and realizing reusability such as Falcon 9. The goal of this article is increasing the accuracy and safety of the guidance and control system of the launch vehicle in order to successfully land on the ground station. Integrated guidance and control, being a novel method in guidance and control, is used to guide the launch vehicle in the re-entry phase and landing phase on the ground. The returning object studied is a Falcon 9 rocket for which we find the 6 DOF model. This vehicle has a vertical landing phase and implementing an integrated guidance and control system is a novel approach in this area. The controller used in this article is based on sliding-mode. This controller has an acceptable performance against the uncertainties and indefinite values of the system parameters. GPOPS software is used to create the initial flight path of the launch vehicle. This software calculates the optimal landing path with respect to dynamic constraints, control constraints and a cost function. Genetic algorithm is used to find the constant parameters for guidance and control. In this work, a fast terminal sliding mode control is proposed for a VTVL reusable launch in the present of disturbance and uncertainties. Compared with the previous works, the proposed controller has satisfactory performances and achieves smaller steady-state error under the consideration of multiple simulation results. Results show that integrated guidance and control needs less bulk standard deviation than common guidance and control due to simultaneous solving of guidance and control equations. This causes the defined constraints not to surpass the acceptable values anywhere in the path.