Optimal Manoeuvres for Space Manipulators Deployment

High cost and risk related to manned space mission calls for the automation of in-orbit activities. Several tasks currently performed by astronauts could be indeed exploited by servicing orbiters, conceived as graspers with arm-like appendages. This paper aims to present the first findings of a research program recently started at the University of Rome "La Sapienza", including theoretical, numerical and experimental aspects. Dynamics of multibody systems obviously apply to this special kind of manipulators, which peculiar asset is their intended operations in a free, completely unrestrained configuration. The study of the motion of a free-flying robot is rather more complex than the study of a similar system working on the Earth. A coupling between attitude and orbital dynamics results, leading to special requirements of analysis and simulation of this complex system. Space graspers need suitable laws for the guidance of the arms, in order to "capture" the to-be-repaired spacecraft and therefore perform the required fixes. Furthermore the attitude control of the in-orbit platform has to be fulfilled, in order to compensate the attitude variation of the grasper due to the manipulator motion. This paper presents the study of a 2D flexible manipulator. The dynamic equations are recalled. The optimization of both the guidance law for the arms and the attitude control of the platform is carried out, taking into account also the flexibility of the arms. Extensive numerical simulations are presented to validate the approach.