Design of thrust vectoring attitude control system for lunar lander flying testbed

The proposed work has been developed within the project LEAPFROG (Lunar Entry and Approach Platform For Research On Ground) at the University of Southern California. The project concerns the realization of a lunar lander test bed prototype with the aim of testing GNC algorithms for simulated lunar flight and descent. The main focus is the realization of a newly designed thrust vectoring system (TVC) that exploits the thrust given by a main engine in order to control the attitude of the platform. This new attitude control system is combined with current traditional reaction control system (RCS) based on cold-gas thrusters. After a preliminary hardware design phase, a linear LQR controller, based on a reduced quaternion model, and a non-linear sliding mode controller are designed for the TVC system. Linear Quadratic Regulator offers a simple implementation, an optimal control law. However it can be affected by un-modeled dynamics and the solutions provided are, in general, only locally valid. Sliding mode control (SMC) guarantees robustness against disturbances, unmodeled dynamics and uncertainties about the mass properties of the prototype, offering also a global stability. Cons of this method are the hard implementation and the request of an high-frequency actuation. A MATLAB/Simulink simulation is set up in order to validate and compare the designed controllers and to analyze if the thrust vectoring system leads to the desired results.