Sensitivity Study Regarding ABS Formulation on Hybrid Rocket Performance

Acrylonitrile butadiene styrene (ABS) has emerged as a widely adopted solid fuel for hybrid rocket propulsion due to its compatibility with fused deposition modeling and favorable regression characteristics. As a terpolymer, however, ABS monomer mass fractions vary across commercial sources, introducing thermochemical variability that is rarely accounted for in propulsion modeling. This study presents a sensitivity analysis examining how compositional variability among ten commercially available ABS feedstock propagates into hybrid rocket performance predictions. Each source was characterized using bomb calorimetry and Fourier-transform infrared spectroscopy to derive source-specific constituent mass fractions and enthalpies of formation, which were supplied to NASA’s Chemical Equilibrium with Applications code to evaluate characteristic velocity under gaseous oxygen combustion. The second objective of this work is to determine which characterization and modeling workflow is sufficient for that purpose by quantifying the sensitivity of characteristic velocity predictions to the enthalpy of formation values derived from bomb calorimetry versus Fourier-transform infrared spectroscopy combined with the Van Krevelen group-contribution method. The two pathways yield enthalpy estimates that differ by 2.4–25.9 kJ/mol, but these differences propagate to less than 0.5% in predicted characteristic velocity across all 3D-printed filaments, indicating that the simpler group-contribution approach is adequate for routine performance prediction while direct calorimetry retains independent values for material qualification. The results demonstrate that assuming a single canonical ABS formulation introduces meaningful uncertainty in predicted characteristic velocity and that experimental feedstock characterization should be considered standard practice in hybrid propellant development.