The rocket-based combined cycle (RBCC) engines are a hybrid between rocket and air-breathing propulsion. They can offer performance gains when compared to traditional rocket engines. At the same time, they are relatively simple in design. Therefore, they generally do not require long development times or large funds so they could be an attractive alternative to rocket-only propulsion.

This thesis presents research on RBCC engines with the main goal to investigate possible use of this type of engine aboard the Mk-II Aurora suborbital spaceplane that is being developed by Dawn Aerospace. The main criterion used in the assessment was the impact of implementing the engine on spaceplane's performance compared to current rocket-only propulsion.

In this study a RBCC engine was designed based around the parameters of the core rocket motor. During the initial phase, the engine was optimized for performance using a developed and validated quasi-1D model. This design was then analysed using CFD methods to verify results of the early simulation. Later on the quasi-1D model was used to simulate engine operation in multiple flight conditions. Finally, the trajectory was optimised and compared with the trajectory of a rocket-propelled spaceplane to investigate the final performance gains. It was concluded that only a modified version with added compressor could possibly match or outperform rocket-only propulsion but only if its design does not add more than the threshold mass and drag to the existing spaceplane design.