Terminal Phase Descent Trajectory Optimization of Reusable Launch Vehicle

Abstract

Optimization of terminal phase descent trajectory of winged reusable launch vehicle is studied in this paper. This trajectory consists of ‘Terminal Area Energy Management (TAEM)’ phase and ‘Approach and Landing (AL)’ phase. Three dimensional dynamics of an unpowered winged launch vehicle over a rotating Earth and an oblate gravitational field, is considered. The objective of the trajectory optimization is to land the vehicle horizontally on a predefined runway, using angle of attack and bank angle command, satisfying the path constraints of dynamic pressure, load factor and control limits, and terminal constraints of position, horizontal velocity, sink rate and heading. Trajectory is optimized using Chebyshev pseudospectral knotting method, wherein the state and control variables are discretized at Chebyshev-Gauss-Lobatto (CGL) points and the problem is converted to a nonlinear programming problem. The versatility of the formulation is demonstrated by obtaining optimum trajectories for a variety of initial conditions and cost functions and the analysis of the optimum trajectories are presented.