Experimental validation of a drogue estimation algorithm for autonomous aerial refueling

Autonomous docking for airborne energy transfer is an important unmanned aerial vehicle capability that has yet to be accomplished. The implications of this technology are far reaching because vehicle endurance can be significantly extended without requiring additional onboard energy storage or environmental energy collection. A major barrier to docking with a drogue is reliable and accurate knowledge of the drogue´s state, relative to the aircraft that is performing the manoeuvre. We address this by propagating a derived cable-drogue dynamic model using onboard sensor measurements, then correcting the state and aerodynamic coefficients with air-to-air visual observations. The approach is verified through a series of close formation flights with a marker based infra-red vision system. These flights represent significant progress toward an autonomous docking demonstration.