Improved Sliding Mode Tracking Guidance for Mars Powered Descent Phase

In order to make sure that the Mars lander can track the reference trajectory quickly in the powered descent phase, an improved sliding mode tracking guidance law is designed. The guidance law is composed of an enhanced exponential reaching law and a nonlinear sliding surface. The main advantage of this guidance law is that the lander tracks the desired trajectory without chattering phenomenon in a finite time. Besides, to guarantee the actual output thrust satisfying the engine thrust magnitude constraint, a saturation function is applied to the limit the output thrust of the lander. The effectiveness of the proposed sliding mode guidance law is verified by numerical simulations.