The integration of high-speed airbreathing engines into dedicated small satellite launchers may allow for some of the stages of the launch system to be reused, resulting in improved cost efficiency and turnaround times. Designing a trajectory of this type is challenging, due to the high number of competing performance drivers and design constraints, which are often in opposition with each other between the different modes of flight (i.e. airbreathing, rocket, and glide). In this work the design of the trajectory for a partially airbreathing rocket–scramjet–rocket multistage launch system is studied by generating optimal trajectories using the pseudospectral method of optimal control for maximum payload-to-orbit. This optimization simultaneously determines the ascent of all three stages, as well as the return trajectory of the scramjet stage within the trajectory optimization. It is found that the scramjet accelerator is able to achieve fly-back to its initial launch site, but that it must ignite its scramjet engines during its return flight, causing this to become an important consideration in the optimal trajectory design. This work shows that the return of the scramjet stage of a rocket–scramjet–rocket launch system may be feasible, and indicates the trajectory features that may heavily influence future partially airbreathing launch system designs.
The structured grid is made up of 265 blocks and is generated using e3prep, the preprocessor and grid generation tool for The University of Queensland's compressible CFD code, Eilmer. Significant modification of vehicle geometry is possible while retaining acceptable grid quality. However, poor quality issues present themselves at swept geometry.In addition to a demonstration of the parametric nature of the tool, results of a proof of concept simulation of the complete vehicle are given. A short forebody study detailing the analysis of a widened, cambered forebody with a flattened windward side was completed as further demonstration. The modified geometry was found to improve the inlet onset flow iii and increase precompression. These results are presented without formal verification and validation and hence considered provisional.Recommendations are made on the continued development of the tool. These primarily address the quality issues preventing full functionality of the tool and include utilising sections of unstructured cells to form a patched grid and combining the current work with GridPro for the generation of a highly smoothed grid. The use of OpenFOAM for subsonic simulation is also discussed along with increased parallelisation of the simulations to decrease runtime.
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