Feasible zone for planetary entry vehicles

Understanding the coverage of ground track is conducive to evaluating an entry vehicle's maneuver capability, especially for an entry mission with waypoint constraint. This paper investigates a feasible zone which describes the lateral corridor of the entry vehicle's ground track. Any point inside the feasible zone is supposed to be reachable from the initial condition and controllable to the terminal condition. Analyses show that the zone boundary consists of two or three phases. For each phase, the zone boundary is generated by solving one or more trajectory optimization problems. The feasible zone can be employed to judge whether or not a waypoint is feasible to the vehicle. Moreover, to evaluate the feasible level of the waypoint, an evolved feasible zone with pass index is defined and calculated. The feasible zone is simulated for an Earth entry vehicle in various missions. Dispersions are considered in the simulation to analyze the influence of aerodynamic uncertainties.