Entry Guidance for the X-33 Vehicle

The entry  ight of the X-33 AdvancedTechnologyDemonstrator is Ž rst examinedby usinga trajectory optimization approach. For closed-loop guidance the nominal entry trajectory is deŽ ned by a piecewise linear drag vs an energy proŽ le. Under a nonlinear tracking control law and an onboard drag-proŽ le 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.