Terminal area guidance for reusable launch vehicles

In this paper, a ranging-capability-estimation approach and an adaptive guidance law are developed for reusable launch vehicle during the terminal area energy management. The reference trajectory is planned within the neighborhood of the center of ranging capability. To estimate the ranging capability, a group of algebraic formulas are derived to compute its upper boundary, and an iteration logic is investigated to compute the lower boundary. This approach is simple and potential to be used on-board. A more precise range prediction and the consideration of bank angle and normal acceleration constraints improve the feasibility of the planned Shuttle-based ground track. In the longitudinal guidance, a new dynamic-pressure tracking scheme is designed to combine with the tracking of a reference altitude profile. This combination strategy guarantees the controlling of altitude, velocity, and flight-path angle. Finally, an automatic gain-tuning method, based on the feedback linearization technique, is developed for the proportional and derivative gains in the trajectory-tracking law. Numerical simulations of the X-33 demonstrate that the proposed ranging-capability-estimation approach has high precision, and its computation time is short; the new guidance law can automatically deliver the reusable launch vehicle to the desired approach and landing interface state even when there are initial-state dispersion and flying disturbances.