Velocity-free prescribed performance control for spacecraft hovering over an asteroid with input saturation

This paper investigates the input constrained prescribed performance control (PPC) for asteroid hovering merely using position measurements. The controller guarantees the position error converges to a prescribed residual set with desired transient performance in the absence of sensed velocities. First, the position error is transformed into a new error variable and a proper error dynamic system is established according to the PPC methodology, based on which, a backstepping prescribed performance controller is devised with the input saturation handled by an auxiliary system. Then, a state observer is developed by employing the immersion and invariance (I&I) technique, and the estimate is substituted for the velocity in the controller; meanwhile, the auxiliary system is improved to handle the input saturation of the velocity-free controller. The closed-loop systems stability is established via Lyapunov analysis. Finally, simulations are conducted to validate the effectiveness of the proposed scheme.