Virtual Trajectory Augmented Landing Control Based on Dual Quaternion for Lunar Lander

A pinpoint soft landing with a low touchdown velocity is critical for a lunar lander in the terminal landing phase, particularly with respect to scientific exploration missions. However, the main descent thruster of the lander is usually equipped on one side along the body axis, whereas reaction thrusters for attitude control are fixed in three axes. This causes the translational dynamics and the rotational dynamics of the lunar lander to be mutually coupled. In this study, a new force-torque sequential control law is introduced to resolve the coupling effect. To further improve the coupled motion, a virtual landing trajectory augmented control law is designed. The virtual trajectory is represented as a virtual quaternion and is augmented as a command to the lander's position update using the dual quaternion. A combined augmented landing control algorithm is newly proposed to incorporate the virtual trajectory commands into the force-torque sequential control law. Numerical simulation results with some cases by the MonteCarlo method show that the designed augmented control system enables a terminal soft landing with less fuel consumption.