Leader–Follower Formation Trajectory Planning for Unmanned Reentry Vehicles Based on Quasi-Equilibrium Glide

The strong nonlinearity, coupling, and underactuation characteristics severely constrain the formation guidance and trajectory planning of reentry glide vehicles (RGVs). To address this issue, this paper proposes a novel distributed leader–follower cooperative guidance framework for multiple RGVs under the quasi-equilibrium glide condition (QEGC). For the leader RGVs, an analytical bank angle solution derived from the QEGC is enhanced with a non-singular terminal sliding mode (NTSM) correction strategy that tracks an exponentially decaying reference altitude rate, effectively suppressing altitude oscillations and improving trajectory smoothness. Simultaneously, an analytical flight-path angle solution is introduced to refine terminal altitude accuracy, complemented by a corresponding angle-of-attack correction method. For followers with limited communication access to the leaders, a fixed-time distributed observer is designed to estimate the formation center states using only neighbor-to-neighbor information exchange, ensuring fast convergence independent of initial conditions. A distributed formation control law incorporating neighbor coordination is then developed, enabling followers to track the leader's commands while maintaining the desired planar formation geometry. Numerical simulations demonstrate that the proposed guidance scheme achieves stable formation keeping in the latitude–longitude plane throughout the glide phase, with smooth trajectories, accurate terminal constraints, and robust performance under initial dispersions.