Research on Optimization of an Accelerated Trajectory for Ramjet-Powered Vehicle

In order to investigate the optimum ascent trajectory of an air-breathing vehicle, a strategy is identified to find out the optimal trajectory required for the ascent phase of a general supersonic vehicle propelled by a ramjet. The accelerator vehicle operates approximately from Mach 2.7 to 6.0 (altitude 19km to 25km). The system model is established with an ideal ramjet model and a vehicle dynamic model in the vertical plane. Considering with two different objective functions and also unstartprotection constraint, minimum-fuel and minimum-time trajectory problems are formulated, and then solved via Gauss Pseudospectral Method. The results show that the essence of trajectory optimization problem is match engine performances with atmosphere characteristics. Compared with that along the minimum-time trajectory, a vehicle with 1000 kg weight operating along the minimum-fuel trajectory can reduce fuel consumption by 4.7% but requires 30.3% more time. It is also found that the take-off weight has an obvious influence on optimum trajectories, and a heavier vehicle needs more dynamic pressure before climbing.