Ascent Trajectory Optimization of Launch Vehicles with Air-Breathing Propulsion

Abstract

Abstract This paper aims to investigate optimization of a highly constrained three-dimensional trajectory of a launch vehicle stage powered by air-breathing engine, with oblate gravitational field. The trajectories of such vehicles are difficult to optimize, owing to strong nonlinear coupling between the thrust, aerodynamics and the vehicle’s states, and stringent constraints on structural load and aerodynamic heating. The objective of trajectory optimization is to impart maximum velocity at a desired altitude and direction, with minimum fuel consumption, using angle of attack and engine throttle as control inputs. Path constraints on dynamic pressure, bending moment, and heat flux as well as control constraints need to be satisfied. Trajectory is optimized using the approach of discretization of control variables, which converts this optimal control problem to a nonlinear programming (NLP) problem. This NLP problem is solved using a metaheuristic method (harmony search optimization), and the sensitivity of the solution with respect to discretization is also analyzed. The versatility of trajectory planning method is demonstrated by solving the problem with different initial conditions, objectives and constraints.