Dynamics and control of free-flying manipulators capturing space objects

Abstract

Based on the barycentric vector and direct path approaches, the kinematics of a multiple arm space robotic system is developed, and the differences between the two formulations are discussed. Applying the general Lagrangian formulation, a concise explicit model of the system dynamics is derived, and the specific characteristics of space robotic systems as compared to fixed-base manipulators are discussed. Coordination between a spacecraft and its multiple end-effectors, based on planned trajectories, is investigated in capturing a moving space object. Two model-based control algorithms, based on an Euler angle and an Euler parameter description of the orientation, are proposed as well as a transpose Jacobian controller. Simulation results are presented to evaluate the developed controllers and the planning strategy, in both planar and three-dimensional maneuvers. To control coordinated motions of space robotic systems, a new Modified Transpose Jacobian (MTJ) controller is presented which yields an improved performance over the standard algorithm. Simulation results show that the performance of the MTJ law is comparable to that of model-based algorithms, even though it requires a reduced computational effort. To manipulate a captured object by multiple manipulators, a new Multiple Impedance Control (MIC) algorithm is developed which enforces an identical controlled impedance on each participating manipulator, on the manipulated object, and (in space) on the free-flying spacecraft. The similarities and differences between the developed MiC law and other force/impedance controllers are investigated, and simulation results are presented.