This paper proposes a new strategy for space teleoperation under communication time delay, which makes it possible for an operator to know conditions of a remote manipulator through force reflection of the time delay. Using the proposed strategy, an operator feels as if the manipulator is operated through a virtual spring. Basic algorithm is that difference of command and telemetry data due to the time delay is displayed to an operator by force reflection of a hand controller. Also, the force reflection includes a contact force applied to the manipulator. In operation without contact, the force reflection becomes to be zero when the manipulator finishes its motion. Under condition of contact, the force reflection continues to be applied even if the manipulator stops its motion. Change of the force reflection suggests: occurrence of contact; force release of the manipulator; and manipulator moving. The effectiveness of the proposed approach was confirmed by teleoperation experiment.

We discuss a new type of space robot system composed of a spacecraft and a robot attached through a tether to it. The tethered robot is translated away from the spacecraft using existing tether tension control techniques in gravitational field. Link motion of the tethered robot, however, is complicated, since the momentum is not constant due to the presence of external forces. This paper especially focuses on momentum control of the tethered robot. In addition to translational momentum control, we show that angular momentum of the tethered robot can be controlled by proper motion of the tether attachment point. We propose a control law for link motion of the tethered robot composed of two subtasks: the end-effector motion subtask and the tether attachment point motion subtask.

In our previous study we introduced a new type of space robot system, which consists of a spacecraft and a robot attached to it via a tether. In this paper, the characteristics of the system in gravitational field are described and a path planning approach is proposed. The translational motion of the mass center of the robot is controlled by tether tension. The path planning approach ensures end-effector motion along the desired path. In addition, proper motion of the tether attachment point is obtained, such that tension control can take effect. The effectiveness of the approach is examined by computer simulations.

The authors previously (1996) proposed a new type of space robot system, consisting of a spacecraft and a robot attached through a tether to it. This system is called a "tethered robot system." In this paper, we clarify the characteristics of the tethered robot system, and especially focus on position control of the center of mass of the robot. Tether tension is used to control the position, taking into account the gravity gradient and the centrifugal force. The results from the trajectory planning procedure suggest that the shape of the path depends both on the direction to the destination point and the time to accomplish the mission, it does not depend on the distance. From the simulation results with feedforward control it is concluded that accurate path planning is possible only if the destination point is close to the initial point, or if the time to accomplish the mission is long enough.