Dual-quaternion immersion and invariance velocity observer for controlling asteroid-hovering spacecraft

This paper investigates the velocity-free spacecraft pose tracking control in terms of dual quaternions, and its application to six-degrees-of-freedom (six-DOF) asteroid-hovering operation. First, a coupled linear velocity and angular velocity observer, driven by the spacecraft position and attitude measurements, is designed via the immersion and invariance (I&I) methodology. After dominating the nonlinear terms in the pose dynamics due to rotation motion by high-gain injection, the observer is shown to be exponentially convergent. An output-feedback pose tracking law is then derived by combining the proposed velocity observer and a full-state feedback proportional-derivative controller with a proven separation principle. Finally, an asteroid hovering operation with the proposed method is simulated to demonstrate its effectiveness and application.