Entry guidance for the X-33 vehicle

The entry Eight of the X-33 Advanced Technology Demonstrated is first examined by using a trajectory optimization approach. For closed-loop guidance the nominal entry trajectory is defined by a piecewise linear drag vs an energy profile. Under a nonlinear tracking control law and an onboard drag-profile updating scheme, the vehicle reaches the designated target point accurately. To further meet the stringent heading requirement at this point, a ground-track design method and the corresponding trajectory control law, which can be applied at a distance before the vehicle reaches the target point, are developed. Simulations with the X-33 vehicle and trajectory data demonstrate good performance of the guidance algorithms.