Trajectory linearization control based tracking guidance design for entry flight

A novel use of trajectory linearization control (TLC) method was introduced in the guidance law design for hypersonic vehicle entry flight. By exploiting the inherent characteristics of time scale separation of entry vehicle dynamics, altitude and velocity could be controlled separately via outer and inner loop design. In the outer loop, path angle was used as pseudo-control for controlling the altitude. In the inner loop, the flight path angle command and velocity were tracked using bank angle and angle of attack as controls. A linear time-varying controller was designed for the feedback loop to stabilize the error dynamics. Feedback gains were computed online and are the symbolical functions of reference trajectory, therefore no explicit gain scheduling or mode-switching were needed. Extensive dispersion simulations show that this guidance algorithm can achieve precise trajectory tracking and is trajectory-independent. The simulations also show that an integrated entry guidance approach which combines the use of TLC-based tracking guidance law design and on-board reference trajectory planning can significantly enhance the autonomy and adaptability of entry flight.