Underactuated attitude tracking control of tethered spacecraft for deployment and spin-up

This paper investigates the underactuated attitude tracking control problem of tethered spacecraft during tether deploying and spinning. The attitudes are controlled by the torque inputs along two body axes and perturbed by the tether tension torque. The coupling effect between spacecraft attitudes and flexible tethers can be alleviated by simplifying control inputs. The main contribution is the development of an underactuated tracking controller with an adaptive barrier function that inhibits unknown disturbance. To avoid singularity problems with tether and spacecraft during simulation, the dynamic model of a tethered system is derived using quaternion transformations. The underactuated attitude control strategy is designed by kinematic state coupling relations and dynamic backstepping technique, which is given extensive stability demonstration using Lyapunov's theory. An adaptive controller gain with barrier function is employed to inhibit the bounded unknown disturbance with no need for the online estimation signal. Finally, numerical simulations demonstrate the effectiveness and robustness of the proposed underactuated strategy in the case of tether deployment and spin-up, respectively.