# Tutorial Review on Space Manipulators for Space Debris Mitigation
## 5 Space Manipulator Operations--Evolution from Teleoperation to Autonomy
A haptic interface is a bidirectional device that permits the human operator to experience the applied forces at the remote site at high update rate. Transparency requires that the impedance from the remote site \(Z_{e}\) must be transmitted to the human operator \(Z_{t}\) without distortion such that \(Z_{t}=\frac{f_{m}}{\varphi_{m}}=\frac{f_{e}}{\varphi_{s}}=Z_{e}\) where \(f_{m,s}\) = master/slave forces, \(v_{m}\) = master/slave velocities. However, perfect transparency requires zero inertia and infinite bandwidth through instantaneous channels. Direct bilateral force-reflecting feedback is a major problem for time-delayed teleoperated systems in generating instability due to mismatched dynamics. Time delays in transmitting force feedback from the slave to the master generate instabilities particularly beyond 500 msec corresponding to human reaction speed. Any latent time delays beyond this tend to increase task error rates and completion times due to move-and-wait strategies being adopted by the human operator. The robust Ho controller with \(\upmu\)-synthesis can provide stability for prespecified short time delays only [91]. In this case, the use of calibrated 3D graphical predictive displays overlying the actual view of the remote robot permits the operator to interact with the models in real-time [88]. High model dynamics fidelity and accurate least squares calibration is essential. Impedance control has been proposed for bilateral force reflection in teleoperation [92]. Short time delays of up 100 msec have the effect of increasing effective impedance during capture operations while reliable capture favours minimising manipulator impedance to minimise the manipulator contact force [93]. A real-time teleoperative link with telepresence requires a very low latency of \(\sim\)50 msec or less for effective force reflection. Nevertheless, force feedback of remote forces with a PD feedback controller may be used under significant time delays \(\sim\)1-2 s and beyond, albeit at much reduced task performance rates. Force reflecting hand controllers can utilise attractive and repulsive potential fields of virtual forces at the remote end effector to form virtual corridors that output predictive forces at the hand controller to indicate the desired motion required by the operator [94; 95]. The main approaches to dealing with stable teleoperation with constant time delay are [96]: (a) passivity theory; (b) hybrid compliance control/impedance matching control; (c) model predictive control; and (d) adaptive control. Shared compliant control involves autonomously closing the feedback loop at the robot (slave) side which also employs a passively compliant hand the response of which was fed back to the human operator [97]. It involves reducing the force reflection signal by reducing the error between the master and delayed slave positions. Model predictive controllers which implement learned models will possess similar advantages to predictive graphics. Passivity-based approaches do not require models of the environment, unlike predictive approaches. Passivity theory dictates the transfer of velocity and force information between master and slave [98]. A system is passive if the power of the system is either stored or dissipated:  
\[P=\frac{dE}{dt}+P_{d}\text{ where }E\;=\;\text{energy stored},\;P_{d}\;=\;\text{power dissipated} \tag{8}\]If power dissipation is positive, the system is passive.