Air Force Research Laboratory Munitions Directorate Through Sargent Fletcher, Inc.
1 September 2003 – 30 June 2004
Co-P.I.s John L. Junkins, Donald T. Ward, and David W. Lund
Total Award $100,000
This project will flight test the first closed-loop hook-up of two Unmanned Air Vehicles (UAVs) in a simulated air-to-air refueling configuration. It is the critical step toward a practical and routine Autonomous Air Refuleing (AAR) capability to extend the range and endurance of Class III air vehicles (between 5 and 200 pounds). This project will also further develop the VisNav vision based relative navigation system, and synthesize control laws to enable accurate AAR. Since only slight modifications to legacy refueling systems are required, this technique has the potential to minimize costs required to upgrade manned refueling assets to autonomous refueling. Four phases are planned. The objectives of Phase I include demonstrations of both ground-to-ground and air-to-ground autonomous docking maneuvers, and development leading to the air-to-air flight demonstration of Phase II.
A high-fidelity simulation will be created, consisting of the VisNav sensor, the tanker air vehicle, and the receiver air vehicle. This high fidelity model of the VisNav system will be used to validate the adequacy of the VisNav navigation solution for AAR. The VisNav model will include realistic sensor noise, field of view considerations, and provisions for various lighting conditions. The model will be validated using experimental data and/or existing VisNav simulations. The tanker UAV is the Maxdrone, supplied by Lockheed Martin Aeronautics. State-space models of the Maxdrone will be modified to include the effects of the triangle boom assembly, a specialized refueling drogue for refueling small air vehicles. If necessary, an autopilot that will allow the tanker to maintain steady, level 1-g trim during the docking maneuver will be developed. The Boeing Air Dominator is the reciever UAV, and state-space models based on data supplied by Boeing will be incorporated in the simulation. A flight controller which incorporates measurements from the VisNav relative navigation sensor will be synthesized for the end-game docking maneuver, and implemented on the Air Dominator.
Presently there are two control structures that have been designed and simulated for AAR. The first is Nonzero Setpoint (NZSP), which enables the receiver vehicle to dock with a stationary refueling target. This controller will be used in the Phase I ground-to-ground test, where a robotic mobile platform carrying VisNav equipment will dock with a port on the laboratory wall. The second control structure is the Proportional Integral Filter Command Generator Tracker with Control Rate Weighting (PIF-CGT-CRW) developed by Kimmett and Valasek for the Autonomous Aerial Refueling of Unmanned Air Vehicles program presented below. This control structure allows the receiver vehicle to track a pre-defined trajectory of the refueling boom.
A set of scenarios will be created to test the operation of the AAR system in different operating conditions involving various tanker and receiver vehicle relative range and velocities, various lighting conditions, and disturbance effects. These scenarios will first be evaluated by simulation, and ultimately flown.
Working with me on this program are Graduate Research Assistants:
- Roshawn E. Bowers
- Changwha Cho
and Undergraduate Research Assistants:
- Zach Reeder
- Kyle Schroeder