Trajectory optimization for a TBCC-powered supersonic vehicle with transition thrust pinch

Transition thrust pinch is a critical issue of Turbine-Based-Combined Cycle engines when vehicles operate at trajectories with constant dynamic pressures. The insufficiency of the net thrust might cause that the vehicle fails to accelerate over mode transition from a turbine engine to a scramjet engine and then lead to mission abortion. Existed solutions to this problem mainly focus on increasing thrust of propulsion systems by using auxiliary power units when transition thrust pinch occurs. Without bothering to develop new propulsion systems, this paper turns to trajectory optimization to change the thrust and drag status of the vehicle to gain an additional net thrust. Additionally, the gravity-assist strategy is also used to make up for the thrust pinch in optimized trajectories. The transition thrust pinch issue is abstracted into an optimal control problem with the maximum terminal speed as the cost function, which is then solved via the Gauss pseudospectral method. Firstly, the effectiveness of this strategy is demonstrated by several cases with transition thrust pinch issues. Then, the upper-limit of this method is analyzed. Finally, this study indicates that the limited capacity can be broaden by loosening the constraint on the minimum dynamic pressure.