A joint is provided for unfolding systems, e.g. for satellite solar generators that permits sufficiently large unfolding torque, low weight and small dimensions. A drive on one joint half acts on a small pulley to wind a cord on it. The other end of the cord is tautly connected to a large pulley that rotates on the hinge pin and is fixed to the second joint half. The large pulley rotates in the opposite direction of the small pulley when the cord is wound so that the second joint half folds away from the first joint half on the hinge pin into an unfolded state and is held in this state by a stop against the tension of the cord. The joint is used, for example, for unfolding joints for satellite solar generators that consist of two joint halves, a hinge pin and a drive.