3D minimum reaction control for space manipulators

This paper presents a novel controller for a generic 3D multibody space system. The control is designed to minimize the dynamic coupling between one of the bodies and the rest of the system, e.g. a spacecraft endowed with a robotic manipulator. Standard control techniques suffer of some limitations. For instance, the Jacobian Transposed (JT) control does not explicitly address the reduction of the reaction forces over the main body. Or else, the so-called “Reaction Null” (RN) technique has a limited workspace due to the strictness of the constraint of zero reactions over the spacecraft. A new closed-loop controller, called Minimum Reaction (MR) control, is designed by combining the RN and JT approaches, so that the dynamic coupling between base platform and manipulator is reduced, while achieving the desired end effector position with great precision. In fact, the reactions on the base are minimized but not constrained to be null as in RN, so that the workspace of the manipulator is extended at its maximum. To this end, the non-linear 3D dynamics of a multibody system is derived in matrix form. Then, a minimum reaction control problem is formulated and solved analytically using a quadratic cost function. The presented solution is applied to a typical mission scenario involving a robotic arm deployment, both in the case of a rigid multibody system and in the case in which a flexible appendage (such as a solar panel) is included. Results are compared with a Jacobian Transposed controller and a Reaction Null controller and discussed.