Time-to-Intercept Adaptive Sequential Convex Programming for Fixed-Wing UAV Evasion Against Kamikaze Interceptors

When a fixed-wing UAV on a time-critical mission is engaged by a high-speed kamikaze interceptor, the onboard planner must simultaneously guarantee threat evasion and sufficient mission progress to reach the designated landing zone within the prescribed time budget. This paper breaks the deadlock with a Time-to-Intercept (TTI) adaptive Sequential Convex Programming (SCP) planner embedded in a three-dimensional Stackelberg differential game. A TTI metric, derived from the radial closing speed along the line of sight, classifies the engagement into three regimes - cruise, alert, and evasion - and selects the corresponding multi-objective QP cost weights, enabling seamless transitions between mission-oriented flight and aggressive evasive maneuvering. Within the SCP loop, the interceptor's augmented proportional navigation response is re-predicted at each iteration against the latest evader reference, coupling leader and follower dynamics until convergence to a local Stackelberg equilibrium. Recursive feasibility is enforced through slack-variable relaxation of the linearized keep-out constraints. Comparative simulations across five engagement geometries - rear pursuit, head-on, dive attack, LZ blocker, and lateral block - demonstrate a 100% landing success rate against 80% for the best fixed-weight baseline. A parametric robustness analysis over speed ratio, initial separation, turn rate, planning horizon, capture radius, and load factor delineates the survivable flight envelope, identifying capture radius and speed ratio as the dominant performance-limiting factors.