A system for controlling a tension of a tether between an object and a load tethered to the object comprises magnetorheological (MR) fluid actuator unit(s) including at least one torque source and at least one MR fluid clutch apparatus coupled to the at least one torque source to receive torque from the at least one torque source, the MR fluid clutch apparatus controllable to transmit a variable amount of torque via an output of the MR fluid actuator unit. A tensioning member is connected to the output so as to be pulled by the output member upon actuation of the magnetorheological fluid clutch apparatus, a free end of the tensioning member adapted to exert a pulling action when being pulled by the output member. Sensor(s) provide information indicative of a relation between the object and the load tethered to the object. A controller controls the at least one MR fluid clutch apparatus in exerting the pulling action based on said information.