Space tether deployment control with explicit tension constraint and saturation function

A nonlinear tension control law for the deployment of space tethers is presented, where the positive tension constraint is explicitly accommodated by a special form of saturation function. The feedback in the proposed controller is given analytically in terms of tether length and deployment rate, without the need of full state information. Compared with the recently developed fractional-order tension control scheme, the proposed controller achieves faster tether deployment with better stability. A large set of simulations is conducted to evaluate the performance of the controller and the impact of initial conditions of tether deployment on the convergence characteristics of the system trajectories. The statistical results show that the restriction on the initial conditions for the tether deployment to converge to the desired equilibrium point is quite loose under the proposed control law, which leaves a large margin for practical implementation.