An integral evasion and pursuit guidance strategy for an unpowered air-to-ground vehicle in descending phase

During the descending phase, an unpowered air-to-ground vehicle should accomplish an integral mission, which requires it to evade from a defender and then to attack a target with high precision. On the basis of appropriate hypothesis, the mathematical model of Target-Attacker-Defender (TAD) engagement scenario is established. Then, control saturation, terminal angle constraints on states and velocity are introduced under practical circumstances. Next, the three-dimensional problem is divided into vertical plane and horizontal plane. In vertical plane, a combined guidance strategy with programmed trajectory tracking and trajectory shaping guidance is put forward. The strategy balances the loss of velocity, terminal angle constraint and homing precision. And in horizontal plane, a novel integral guidance law synthesizing evasion and pursuit with specific miss distance is proposed. Eventually, the guidance strategies in two planes are integrated to the original three-dimensional problem. By numerical simulation, the optimal starting point of descending phase is obtained. Consequently, the integral guidance strategy can guarantee the vehicle to evade from the defender with a miss distance larger than 5m and to intercept the target with the precision less than 1m. In addition, the terminal flight path angle approaches to -70 degree while the landing velocity is larger than 2Ma.