Pre-design of an active central mechanism for space docking

This paper discloses the design procedure of a docking mechanism for space applications. The mechanism has to recover the misalignments between two spacecraft, as well as to dissipate the energy due to the relative velocity that is left by the precision limits of GNC system during docking maneuvers. The proposed mechanism is composed of an active part mounted on a chaser spacecraft and a passive one mounted on a target spacecraft. The active part is equipped with a variable length probe made of a linear actuator hinged on an active two degrees of freedom rotational joint. A couple of electrical actuators conveniently installed control the orientation movement of the main one, in order to point it towards a specific housing on the target. The pointing movements are controlled by means of an optical system. A clasping device is placed on the tip of the probe to accomplish the soft docking with a conical seat mounted on the target side. This seat is hinged by a passive two degrees of freedom rotational joint so as to allow it to be oriented under the action of the active probe. Once the rod is inserted inside the conical seat, the probe is retracted. The retraction progressively approaches both spacecraft, and orients them toward the central position. Before the retraction ends a set of passive shock absorbers provides a final alignment. Finally, the hard docking takes place with several hooks creating a stiff coupling between the spacecraft. The main probe actuator and the actuators that control the probe rotation are optimized in terms of relative kinetic energy dissipation, energy consumption and exchanged force reduction during the maneuver between spacecraft. The paper describes the system layout and the different control phases of the docking maneuver. It examines the design parameters in order to provide a preliminary configuration of the mechanism, as well as the main requirements for the mechanical components, actuators, and sensors. Moreover, a 3D mathematical model to study the interaction between target and chaser during docking maneuver is presented. Dynamic simulations have been used to design proper geometries for the mechanical interfaces, to create and tune the parameters of the system components, as well as to define sensors requirements. Keywords: docking mechanism, rendezvous and docking, system optimization, multibody.