Semi-analytical terminal and automatic approach and landing trajectory planners for unpowered reusable launch vehicle
[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] A new guidance scheme for the terminal area energy management (TAEM) phase of an unpowered reusable launch vehicle (RLV) has been developed. The main advantage of the new guidance is the use of the quasi-equilibrium glide (QEG) condition to create a set of analytical functions for different glide-efficiency factors. Then, a coupling between the analytical solution and the ground-track prediction (GTP) is employed to create set of reference trajectories that guide the RLV from the current state to the desired state at approach and landing interface (ALI). The best feasible trajectory is selected by adjusting a geometrical parameters (heading alignment circle (HAC) position and HAC turn radius) based on the minimum residual range between the analytical and geometric ground-track predication methods. Unlike most trajectory planning algorithms, the proposed guidance scheme trajectory does not rely on numerical integration of the governing equations of motion, hence the geometrical parameters are obtained in a very short computational time. The QEG solution is used to create the longitudinal flight reference, while the lateral reference is defined by the GTP method. Standard linearization methods are used to design a closed-loop command in order to track the QEG profile. Furthermore, proportion (P) and proportion-derivative (PD) controls are used to modulate the bank angle during the vehicle flight. The glide efficiency factor is updated in order to make the predicted range satisfactory match the actual range-to-go. Off-nominal conditions, in terms of change in initial downtrack position, crosstrange, heading angle, altitude, flight-path angle, vehicle mass, vehicle drag and atmospheric density are tested using a Monte-Carlo simulation. The simulated results demonstrate the effectiveness of the proposed algorithm to guide the vehicle successfully under large dispersions of initial conditions.
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