  This paper considers a pursuit-evasion scenario among three agents -- an
evader, a pursuer, and a defender. We design cooperative guidance laws for the
evader and the defender team to safeguard the evader from an attacking pursuer.
Unlike differential games, optimal control formulations, and other heuristic
methods, we propose a novel perspective on designing effective nonlinear
feedback control laws for the evader-defender team using a time-constrained
guidance approach. The evader lures the pursuer on the collision course by
offering itself as bait. At the same time, the defender protects the evader
from the pursuer by exercising control over the engagement duration. Depending
on the nature of the mission, the defender may choose to take an aggressive or
defensive stance. Such consideration widens the applicability of the proposed
methods in various three-agent motion planning scenarios such as aircraft
defense, asset guarding, search and rescue, surveillance, and secure
transportation. We use a fixed-time sliding mode control strategy to design the
control laws for the evader-defender team and a nonlinear finite-time
disturbance observer to estimate the pursuer's maneuver. Finally, we present
simulations to demonstrate favorable performance under various engagement
geometries, thus vindicating the efficacy of the proposed designs.
