Adaptive thrust vector control during on-orbit servicing

On-orbit servicing missions often include a final propulsive phase where a spacecraft pushes the other one towards a different orbit. Specifically this is the case of the debris grasping mission where the chaser, after capturing the target by means of robotic arms, has to perform a de-orbit operation. The large thrust involved needs a perfect alignment with respect to the center of mass or the system composed by chaser and target, in order to avoid attitude changes. Such accurate alignment is quite difficult to achieve especially when the characteristics of the target are not perfectly known. A procedure is proposed in this paper, allowing a complete estimation of the center of mass position and of the moments of inertia of the system, starting from the data obtained by the gyros mounted on board of the spacecraft. The output is used to design a maneuver for correcting the target and chaser relative position by moving the robotic arms. Numerical simulations show the proficiency and the applicability of the estimation algorithm and of re-alignment maneuver to a selected mission scenario

A yaw rate tracking control of active front steering system using composite nonlinear feedback

In this paper, the composite nonlinear feedback (CNF) technique is applied for yaw tracking control of active front steering system with the objectives to improve the transient performance of yaw rate response. For lateral and yaw dynamics analysis, nonlinear and linear vehicle models are utilized as actual vehicle plant and for controller design respectively. The designed controller is evaluated using J-turn cornering manoeuvre condition in computer simulation. The simulation results demonstrate that the application of CNF for yaw rate tracking control improves the yaw stability and vehicle handling performances