This paper reports a super twisting sliding mode control strategy applied to a planar tensegrity system. The main objective is to drive the system to a desired angular position while the tensions in the cables are kept within a predetermined range to preserve the prestressed condition characterizing tensegrity systems. Stability conditions for the proposed control strategy are established and closed-loop stability is demonstrated through numerical simulations and experimental validations. In addition, the stiffness variation of the system has been experimentally performed using the same control strategy. Moreover, robustness to external perturbations using the proposed control strategy has been evaluated.