A composite guidance law based on the nonlinear disturbance observer-based control for Mars pinpoint landing

The landing accuracy of a Mars lander is severely affected by a wide range of disturbances at the powered descent stage. To address this problem, a composite guidance law is proposed in this paper. The composite guidance law is developed by the combination of disturbance observer-based control (DOBC) technique and multiple sliding surfaces guidance (MSSG) theory. Compared with other guidance laws, the proposed method achieves promising disturbance rejection performance and high landing accuracy in both position and velocity, reducing the conservatism to a certain extent. The proposed guidance law does not require any off-line trajectory generation and its global stability is verified by using Lyapunov direct method. Simulation results show that the proposed guidance law is superior to the conventional guidance laws in terms of both disturbance rejection and landing accuracy.