Evasive maneuver trajectory optimization for ucav against air to air missile

Abstract

Air combat is a form of combat where survival depends on seconds. The delay in communication of unmanned aerial vehicles (UAVs) with pilots in the ground station is the most important shortcoming in terms of survivability. Near-real-time, high-speed communication methods can be developed to overcome this shortcoming but this requires long-term scientific research and engineering which is costly. The less costly solution to this shortcoming is to develop autonomous operation methods for all possible types of missions that onboard computers will process the information collected by the aircraft's sensors and to take countermeasures against the threats without human input. UAVs that will take a more active role in air combat and contribute to air superiority in the future are named unmanned combat aerial vehicles (UCAVs) and are currently under development around the world. Potential threats to be encountered by UCAVs in air combat can be divided into two groups. They are in-line-of-sight (LOS) threats (air-to-air missiles and guns of the enemy aircraft) at short-range and beyond-line-of-sight (BLOS) threats (air-to-air missiles and air defense systems) at long-range. Within the scope of this thesis, threats of beyond-line-of-sight (BLOS) air-to-air missiles will be addressed for evasive maneuvers. In this study, various combat scenarios are generated and trajectory optimization solutions are obtained to perform autonomous evasive maneuvers for UCAVs against air-to-air missiles without human input. To accomplish this objective, an engagement geometry that includes details of UCAV and missile is introduced. This geometry is constructed by employing factors such as line-of-sight (LOS), velocity vectors, angle of attack, flight path angle, and heading angle, which expresses the relative positions of the missile and the UCAV in 3-dimensional space. UCAV and missile are represented as point-mass models using the given geometry. Along with point-mass models, the commonly used Proportional Navigation (PN) method for missiles guidance is implemented. PN is a guidance method that applies acceleration command perpendicular to the instantaneous Line of Sight (LOS) between the missile and the target, which is proportional to the Line of Sight rate and closing velocity. The relative approaching speed of the missile to the target UCAV is defined as closing velocity. An energy formulation is incorporated into the model to calculate the instantaneous energy consumption of the missile. An optimization algorithm is developed so that the UCAV can automatically command the angle of attack and the bank angle to maximize the instantaneous energy consumption of the missile at every time step using the generated model. Optimal trajectories for different engagement scenarios are automatically generated by the optimization algorithm for variable initial conditions such as the missile's heading angle, altitude, and distance from the UCAV. Thus, it is possible to evaluate the evasive maneuver generation performance of the algorithm in different combat scenarios for short, medium, and long-range engagements. To make the missile-UCAV engagement more realistic, some of the engagements have been repeated by adding noise to the missile's velocity and position data. UCAV has performed successful evasive maneuvers to evade the missile in all of its medium/long-range engagements and one of the short-range engagements. This means that adaptive maneuvers suitable for real combat situations are produced for different initial condition sets.