Optimal control of aerial tethers for payload rendezvous

The exciting concept of using a tether deployed from an aircraft to rendezvous with a ground-based location is successfully demonstrated in this paper. By manipulating the cable attachment point position and the rate of change of the cable´s radial velocity, it can be shown that the tip of a cable being towed behind an aircraft can rendezvous with a surface location. This is achieved through optimal control, using the Chebyshev-pseudo spectral method. This method is quite fast and has excellent accuracy. The results of the optimization found that rendezvous was successful, with all target states being met. The cable tip experiences little motion during the rendezvous maneuver, while the required deployment/retrieval rates arc not excessive. Only a modest amount of control input is required, mostly at the beginning and end of the maneuvering, with rendezvous occurring soon after maneuvering commences. Insights into the robustness of the proposed control scheme are provided.