Cryogenic and semi-cryogenic propellants are the most commonly used liquid propellants for applications in medium-lift launch vehicles. Despite their high performance, the storage requirements for these propellants often lead to complex, heavy, and voluminous structures. The only storable propellant used in medium-lift launch vehicles, UDMH/NTO, comes with its own problems of high toxicity and reduced performance. A promising alternative to this could be storable fuels with highly concentrated hydrogen peroxide (HTP) as an oxidiser. Despite a shorter history of dedicated development, HTP has proved itself an effective oxidiser for in-space applications and small-lift launch vehicles. Therefore, the question could be raised towards the potential of this oxidiser for applications in medium-lift launch vehicles. In this study, the application potential of an HTP-based storable bi-propellant for medium-lift expendable launch vehicles was investigated. To this extent, a large selection of green storable fuels was considered to find the most suitable propellant for this application.

Both the integration and compatibility potential of the propellants and the propulsive and mass performance potential were investigated. The integration and compatibility potential were evaluated through a qualitative assessment based on non-performance-related propellant characteristics. Furthermore, eight fuels were subjected to a more detailed assessment covering the criteria of handling toxicity, environmental toxicity, material compatibility, handling and storage, development level, and coolant qualities. RP-1 was found to be the most suitable fuel with respect to the specific criteria, while ethanol, methanol, isooctane, and isopropanol were also found to be promising alternatives. A launch vehicle model was created to evaluate the propulsive and mass potential of twelve fuels proposed based on earlier findings. This model included a propulsion model, a mass and sizing model, and an aerodynamics and trajectory model, which were all connected through a global optimisation model. In terms of propulsive potential, the cryogenic propellant hydrolox was predicted to have a 25% higher vacuum specific impulse than the best-performing HTP-based propellant DMAZ/HTP. In terms of the specific impulse density, kerosene-derivative fuels in combination with HTP were predicted to have a better performance than hydrolox and than that other conventional storable propellant UDMH/NTO. The optimised gross lift-off mass for the launch vehicle concepts employing HTP was found to be 42-61% higher than the gross lift-off mass of Ariane 6 predicted through the model. Separately, the payload capability of the HTP-based launch vehicle concepts was predicted to be at least 38% lower. In both cases, RP-1/HTP was reported to be the HTP-based propellant with the best performance, while DMAZ, isooctane, and isopropanol could be regarded as suitable alternatives. All of these propellants also outperformed UDMH/NTO. Through a sensitivity analysis, it was discovered that up to 270kg additional payload could be taken to GTO upon considering elevated chamber pressures in the HTP-based engine design. In the end, the high potential and promise of HTP were confirmed as it was concluded that increased development efforts towards HTP-based storable bi-propellant rocket engines could not only lead to a promising alternative to cryogenic propellants but could also allow for the complete replacement of toxic hydrazine-derivative fuels.