Autonomous Collision Avoidance System for Air-to-Air Operations

Abstract

The use of Unmanned Air Vehicles (UAVs) over the past several years has become an important concept for military operations. Currently, multiple UAV flights are not performed due to the difficulty in the control algorithms and the lack of redundancy to handle failures. Control algorithm designs can be achieved to provide for multiple UAV operations but single thread system failures remains a problem. Also, unforeseen circumstances such as ground controllers flying the wrong course can cause air vehicles to arrive in the same airspace at the same time, which can cause a collision. Even in the case of autonomous UAV operation, flight management errors could result in time of arrival errors and air vehicle collisions. As more of these systems are utilized, the methods to control them become even more difficult and the possibility of something going wrong increases. There is also a desire to enable UAV flights within commercial airspace. This desire cannot be achieved until a proven method to prevent air-to-air collisions is implemented. The design of an Automatic Air Collision Avoidance System (Auto ACAS) is intended to prevent air-to-air collisions between air vehicles. The Auto ACAS is not intended to replace existing designs such as the Traffic Alert and Collision Avoidance System (TCAS) but is intended to accomplish a recovery at the last instant to prevent a collision. TCAS and other systems in use today provide situational awareness and traffic advisories to enable pilots to perform de-confliction and manual avoidance maneuver and remain several miles apart. In contrast, Auto ACAS assumes such deconfliction and manual avoidance attempts have not succeeded and operates in a time span that does not allow for manual pilot reactions, thus it must be highly integrated and automated in operation. An automated TCAS could be used to keep apart UAVs and commercial airliners but this kind of design may be difficult to implement due to the fact that it was initially designed to instruct the pilot to make course changes and not automatically take control of the aircraft. Automatic collision avoidance is necessary if Unmanned Aerial Vehicles (UAVs) are to “blacken the sky” in massed attacks, accompany manned fighters on combat missions, and transition civil airspace. These vehicles will, in some manner, have to “see and avoid” other aircraft. An automated air collision avoidance system will fulfill a part of this need. It will automatically maneuver an aircraft, at the last instant, to avoid an air-to-air collision. It will function in a manner similar to a pilot avoiding a AIAA/ICAS International Air and Space Symposium and Exposition: The Next 100 Y 14-17 July 2003, Dayton, Ohio AIAA 2003-2755 This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States. collision. It is a system that must be reliable, verifiable, and partially redundant, forming the last line of defense against collisions. It must provide nuisance free operation and allow safe interoperability. The requirements for such a system will be discussed in detail. Of particular interest are criteria to enable a safe, nuisance free system that will have embedded rules of the road for all encounters. Autonomous control of unmanned aerial vehicles is a goal for the U.S. Air Force in the future. However, flying multiple unmanned vehicles in the same tactical airspace with manned fighters presents very challenging problems. Automatic collision avoidance is a necessary step in moving toward this goal.