Paraffin/HTPB blends for cubesat propulsion: experimental and numerical performance

As CubeSats revolutionize space exploration, the demand for agile, efficient hybrid propulsion has grown. While paraffin-based fuels offer high regression rates, their inherent brittleness limits practical application. This study investigates blending paraffin with Hydroxyl-Terminated Polybutadiene (HTPB) to balance energetic performance with structural resilience. Fuel grains with varying paraffin-to-HTPB ratios (100:0, 70:30, 50:50, 35:65, and 0:100 by weight) were tested in a lab-scale hybrid motor using gaseous oxygen. Performance was evaluated based on regression rate, combustion efficiency, and mechanical stability. Complementary Computational Fluid Dynamics (CFD) simulations modeled internal flow and heat transfer. Results indicate that HTPB significantly enhances mechanical integrity, preventing cracking during handling. While increasing HTPB content reduced regression rates compared to pure paraffin, the blended fuels maintained performance levels suitable for CubeSat missions. The CFD simulations provided robust numerical insights, delivering detailed predictions of the temperature, velocity, and water-mass-fraction profiles along the combustor.