Deployment analysis and control strategies of flexible space manipulators

The dynamics and the control of articulated structures for an in-orbit manipulation is a profitable field of research due to worldwide development. The dynamics and the control of such systems is a challenging task, since the equations that govern their motion are highly nonlinear and the control strategies need to take the limited resources carried on board of the common space systems into account. They refer for instance to limited energy power, limited computational power and limited control power of the actuators; furthermore the base platforms of these robotic systems are generally floating in space or subjected to gravity gradient and other environmental torques and forces. For these reasons an investigation on the deploying strategies for orbiting space manipulators is necessary in order to find the best solutions. In this paper three different control strategies are analyzed: the Reaction Null control, the Jacobian Transpose control and the conventional Proportional Derivative control that are compared in terms of power consumption and of the relevant control efforts. The analysis involves both single and double space manipulator systems. The effects of the elasticity of the motor shafts on the behaviour of the deploying manoeuver are also analysed. Numerical simulations, obtained by a space optimized multibody code, are used for demonstrating the suitability and the proficiency of this kind of control strategies.