Boom and Receptacle Autonomous Air Refueling Using a Visual Pressure Snake Optical Sensor

Autonomous in-flight air refueling is an important capability for the future deployment of unmanned air vehicles, since they will likely be ferried in flight to overseas theaters of operation instead of being shipped unassembled in containers. This paper introduces a vision sensor based on active deformable contour algorithms, and a relative navigation system that enables precise and reliable boom and receptacle autonomous air refueling for non micro sized unmanned air vehicles. The sensor is mounted on the tanker aircraft near the boom, and images a single passive target image painted near the refueling receptacle on the receiver aircraft. Controllers are developed for the automatic control of the refueling boom, and for the station keeping controller of the receiver aircraft. The boom controller is integrated with the active deformable contour sensor system, and feasibility of the total system is demonstrated by simulated docking maneuvers in the presence of various levels of turbulence. Results indicate that the integrated sensor and controller enables precise boom and receptacle air refueling, including consideration of realistic measurement errors and disturbances. I. Introduction There are currently two approaches used for air refueling. The probe-and-drogue refueling system is the standard for the United States Navy and the air forces of most other nations. In this method, the tanker trails a hose with a flexible “basket”, called a drogue, at the end. The drogue is aerodynamically stabilized. It is the responsibility of the pilot of the receiver aircraft to maneuver the receiver’s probe into the drogue. This method is used for small, agile aircraft such as fighters because both the hose and drogue are flexible and essentially passive during re-fueling; a human operator is not required on the tanker. 1‐3 Autonomous in-flight refueling using a probe-and-drogue system is basically a docking situation that probably requires 2 cm accuracy in the relative position of the refueling probe (from the receiving aircraft) with respect to the drogue (from the tanker) during the end-game. This specification is based on the geometry of the existing probe and drogue hardware, and the need to ensure that the tip of the probe contacts only the inner sleeve of the receptacle and not the more lightly constructed and easily damaged shroud. 4 The United States Air Force uses the flying boom developed by Boeing. The boom approach is supervised and controlled by a human operator from a station near the rear of the tanker aircraft, who is responsible for “flying” the boom into the refueling port on the receiver aircraft. In this method, the job of the receiver aircraft is to maintain proper refueling position with respect to the tanker, and leave the precision control function to the human operator in the tanker. 2