The GREEN FOXFIRE project sustainable hybrid propulsion for cubesats based on paraffin-HTPB

The growing relevance of small satellites in space exploration, which in 2023 accounted for 97% of all spacecraft launched worldwide, requires addressing the challenges of propulsion miniaturization. To meet these needs, the GREEN FOXFIRE (Green Fuel and OXidizer For Innovative hybrid Rocket Engines) project investigates compact, efficient, and environmentally responsible hybrid systems, aiming to develop a sustainable hybrid rocket engine (HRE) capable of inserting a 24U CubeSat into Martian orbit from an Earth-orbit transfer. In this work, the performance of paraffin/HTPB fuel blends using gaseous oxygen as oxidizer was evaluated through a combination of numerical simulations and experimental ballistic tests. Paraffin offers high regression rates but limited mechanical strength, whereas HTPB improves structural integrity with lower combustion efficiency. Blended formulations (70/30, 50/50, 35/65, and 25/75 paraffin/HTPB ratios) were analyzed using NASA’s Chemical Equilibrium with Applications (CEA) code and validated experimentally. Results confirmed that paraffin enhances regression rate and combustion efficiency, while HTPB contributes to mechanical robustness. Preliminary design activities also included a four-cluster thruster configuration with dual oxidizer tanks optimized for CubeSat mission requirements. Overall, the study demonstrates the feasibility of green hybrid propulsion as an enabling technology for interplanetary small-satellite missions, combining environmental sustainability with system scalability and performance.