Spacecraft hovering around asteroid via disturbance observer based exponential time-varying sliding mode controller

In this work, a controller based on exponential time-varying sliding mode algorithm is proposed for spacecraft hovering around asteroids. The controller is conducted by adopting global sliding mode which removes reaching phase and is shown to be globally asymptotic stable. To eliminate steady-state error and improve precision, disturbance observer is applied in the control strategy. Importantly, the value of controller parameters depends on a desired maximum velocity of spacecraft. Therefore the proposed controller can achieve speed limit at the same time without another controller. The behavior of the controller has been studied and analyzed. Numerical simulations are given in a flight dynamics scenario in which the spacecraft is asked to hover near asteroid Eros 433 to show the performance of the proposed controller.