A decomposition approach to design attitude controller for underactuated reentry vehicle

This paper presents a new attitude controller design method for underactuated reentry vehicles. Inverse dynamic method can´t be applied to a non-minimum phase system directly, while non-minimum phase problem is inevitable for underactuated reentry vehicles. In order to adopt inverse dynamic method to design attitude controller, a decomposition approach is introduced to cope with the non-minimum phase problem. In this approach, the normal form of 6-DOF equation of motion is deduced. Based on the normal form, the system is divided into two subsystems: a minimum phase one and a non-minimum phase one. And the dynamic equation of the internal dynamics can be obtained. Then the internal dynamics is stabilized with LQR method. Finally, the inverse dynamic controller can be obtained to stabilize the attitude of underactuated vehicle since the non-minimum phase problem is solved by the decomposition method beforehand. Simulation results demonstrate that the stabilization of the internal dynamics is guaranteed and the stable attitude control of underactuated reentry vehicle is also accomplished.