Aerodynamic Tethered Sails for Scientific Balloon Trajectory Control: Small-Scale Experimental Demonstration

High-altitude scientific balloons are often prohibited from flying due to the risk associated with flying over populated areas. One solution to this problem is the use of a trajectory control system to control the ground track of the balloon. To assess the performance of one such trajectory control system in a real wind field, a small-scale sail was designed and built to fly beneath a moored balloon. Three test phases of rudder deflection were used to demonstrate the effect of the sail guiding force on the balloon, and the sail demonstrated the ability to move the balloon laterally due to a change in rudder deflection. A theoretical model of the system was found to qualitatively agree with the experimental values of sail displacement and mooring tether tension. At a high level, these results demonstrate that a tether-and-sail system shows promise as a trajectory control system for scientific balloons.