Optimal Control of an Aircraft-Towed Flexible Cable System

Abstract

The control of an aerial-towed flexible cable system for precision rendezvous and snatch pickup of payloads is considered. In past studies of related systems, optimal trajectories have been determined assuming that the cable remains straight. However, aerodynamic drag and deployment forces can cause bowing of the cable that can significantly alter the position of the cable tip relative to the aircraft. To account for this, the cable is modeled using lumped masses connected via rigid links. Multiple rendezvous sequences using only cable winch control and including features such as collision avoidance and variable winds are solved by multiple-phase direct transcription methods. Numerical results show that for some multiple rendezvous scenarios it is necessary to use the cable lateral dynamics and swing motion to avoid impact with elevated terrain. The effect of different wind speeds and directions are also studied.