Abstract: The deployment mechanism comprises three identical operative assemblies mounted on a fixed main frame. Each operative assembly comprises a linear actuator and first and second links disposed in such a manner as to ensure self-locking in a deployed position by causing the axes of the following three hinges to pass to or slightly beyond a dead point where they are in alignment: the hinge between the main frame and a first zone of the first link; the hinge between the upstream end of the second link and a second zone of the first link; and the hinge between the downstream end of the second link and a link support mounted on the deployable portion of the nozzle. The actuator is secured and anchored to a non-deployable portion of the nozzle and it includes a drive member whose free end is hinged to a third zone of the first link, and it is deactivated in both of the final positions, i.e. when the deployable portion is deployed and when it is retracted.