Space manipulator system (SMS) maneuvers can excite flexible appendages, while fuel sloshing effects impact its dynamics and performance. To predict this behavior and control such systems, sloshing and flexible appendages are modeled. A novel system identification scheme is developed, which identifies all parameters required for the reconstruction of system dynamics despite unmeasurable sloshing and modal states. This is achieved by two identification experiments. In Exp.1 all unmeasurable states are eliminated, while in Exp.2 the unmeasurable sloshing states are eliminated, and a novel estimator is used for the unmeasurable modal states. The significance of accurate SYSID in controller design and performance is demonstrated by simulating a 3D SMS controlled by model-based and robust controllers. In both cases, using the identified parameters results in significant robust control performance enhancement.

To control a free-floating robotic system with uncertain parameters in OOS tasks with high accuracy, a fast parameter identification method, previously developed by the authors, is enhanced further and used concurrently with a controller. The method provides accurate parameter estimates, without any prior knowledge of any system dynamic properties. This control scheme compensates for the accumulated angular momentum on the reaction wheels (RWs), which acts as a disturbance to the robotic servicer base. While any controller using parameter information can be used, a transposed Jacobian controller, modified to include RW angular momentum disturbance rejection, is employed here. Threedimensional simulations demonstrate the method's validity.

An optimal leg sequence selection method is developed, which maximizes hexapod robot stability, considering feasible gaits, motion modes, and terrain slope. A novel and fast search method is employed to find the most stable leg sequence for a given gait; if no such sequence exists, the next fastest stable gait is chosen and the most stable leg sequence for this gait is selected. The method can be based on any stability measure; here the Force-Angle Stability Margin criterion is employed that is sensitive to top-heaviness, and inertial and external forces. Results show that the developed method senses instabilities accurately and selects the best leg sequence for maximum stability far faster than exhaustive searches, offering distinct advantages when varied external forces are applied.

A planning and control methodology for manipulating passive objects using orbital servicers in zero gravity has been developed by the authors. In this work, a parametric sensitivity analysis of the proposed model-based control for the motion of the passive object, in terms of parametric uncertainties, is presented. A linearization methodology is used to provide a scheme with which the controller robust behavior, in terms of parametric uncertainty, can be ascertained a-priori, without the need of running experiments. The system robust performance is illustrated in realistic 3D scenarios and verified via simulations.

Space exploitation will require efficient techniques for manipulating passive objects on-orbit. This work presents a manipulation technique that utilizes both on-off thrusters and manipulator proportional forces to handle passive objects on orbit, canceling the effect of limit cycles on the objects. The system dynamics including the unilateral constraints and the on-off thrusting are discussed. Using a two-layer optimization process, a planning strategy for the trajectory tracking motion of a passive object including optimal end-effector contact point selection, is developed. The manipulation strategy is illustrated using a 3D scenario. A model-based controller adapted to the special characteristics of the system is presented and its response is discussed. The performance of the proposed manipulation system is shown to be promising, while it reduces excessive thruster fuel consumption.

Space exploitation will require efficient techniques for manipulating passive objects on orbit. This work presents a manipulation concept that utilizes both the on-off thrusters and manipulator proportional forces to manipulate passive objects on orbit more efficiently. The system dynamics arising from the unilateral constraints and the on-off thrusting are discussed. The manipulation concept is illustrated using a simplified one-dimensional model. A novel controller based on backstepping and Lyapunov stability is presented and its performance, stability and robustness are discussed. The performance of this system is compared to that of a standard using on-off thrusters only, and is shown to use less fuel.