Deployment control of long-distance space tether systems based on parametric approach

Capture of uncooperative targets using tether-net systems has obvious advantages comparing with traditional rigid capture modes, while the control of such a high flexible plant is tricky. This paper mainly focuses on libraton and vibration attenuation control of the deployment process of a long distance tether-net system. A lumped mass model is built to study the elastic dynamics of the tether system. The deployment control problem is formed as a multi-constrained nonlinear optimal control problem. Piecewise control parameterization and enhancing transformation are performed, which convert the problem into a nonlinear programming problem that can be efficiently solved by the optimal control software package, MISER 3.2. The resulted control law can be easily performed by deployment speed control which requires simple mechanism and no fuel consumption. A compound control frame using tether tension and jet thrusts is proposed to realize exact positioning of the net-capture system in the terminal phase. A robust parametric approach based on eigenstructure assignment is used to design the stabilizing controller. Simulation results based on the lumped mass model show that the proposed control method can effectively attenuate the libration and vibration of the tether system during deployment and realize exact positioning of the terminal net-capture system.