Twistor-based pose control for asteroid landing with path constraints

In this paper, a six-degree-of-freedom (6-DOF) control scheme for asteroid landing subject to collision avoidance and line-of-sight (LOS) constraints is developed within the newly established twistor framework. The controller guarantees a spacecraft touches down at a specified landing site in a desired attitude, meanwhile satisfies the constraints with the coupling effect between the translational and rotational motions involved. First, 6-DOF dynamics of a spacecraft relative to an asteroid is described by the twistor representation to model the translational and rotational motions in a unified way. Then, the collision avoidance and LOS constraints are formulated and expressed as functions of the twistor. Following that, the constraints are encoded into an artificial potential function (APF) and a control scheme that enforces the constraints is proposed by virtue of the APF technique with the stability of the controlled closed-loop system proved via Lyapunov analysis. Finally, numerical simulations are conducted, and the results demonstrate the effectiveness of the proposed controller.