Free Final-Time Trajectory Optimization for Ramjet Mode of ATR Aircraft by Successive Difference-of-Convex Programming

The trajectory design for the ramjet mode of an Air Turbo Ramjet (ATR) hypersonic aircraft has the characteristics of variable specific impulse, variable flow rate, deep coupling between aerodynamic/engine parameters and flight environment/state. To meet the stable operation requirements of ramjet engines, this paper proposes to use the successive Difference of Convex (DC) programming method to optimize the climb trajectory. Employing dynamic dimension expansion method to transform non-convex nonlinear path constraints such as heat flux density, dynamic pressure, and normal load into boundary constraints; By adopting the Bregman regularization improvement strategy, the convex quadratic programming sub-problem of the ramjet mode trajectory optimization problem was transformed, and an improved successive DC programming algorithm was proposed. Simulation results show that the proposed method is suitable for solving the free final-time trajectory optimization problem for the ramjet mode of ATR aircraft. Under the strong coupling of engine, aerodynamic parameters and flight environment/state, as well as dual control variables of angle of attack and valve, the improved strategy based on Bregman function can alleviate the oscillation problem caused by excessively linearized models, improve the robustness and convergence characteristics of the method.