A Preliminary Design Approach to Solid Propellant Formulations for Variable-Thrust Rocket Motors Using CEA Code

Pintle-driven thrust modulation in solid rocket motors imposes strict constraints on propellant flame temperature, pressure sensitivity and manufacturability.Conventional HTPB (Hydroxyl-Terminated Polybutadiene)/AP (Ammonium Perchlorate) composite propellants are widely used but offer limited flexibility when these competing constraints must be balanced.In this work, a preliminary formulation methodology based on the NASA CEA (Chemical Equilibrium with Application) code is employed to systematically investigate NEPE (Nitrate Ester Plasticized Polyether) propellants for variable-thrust applications.HTPB/AP propellants are first analyzed as a baseline to clarify the respective roles of AP and nitramine additives on flame temperature behavior.The results show that flame temperature is dominated by AP content, while excessive nitramine loading may impose unfavorable thermal and operational penalties for pintle-driven hardware.Subsequently, NEPE propellant formulated with inert polymer binders are examined, revealing a restricted compositional design due to coupled constraints on oxidizer loading and flame temperature.In contrast, GAP (Glycidyl Azide Polymer) -based propellants provide a significantly expanded formulation window, enabling improved trade-offs among energetic performance, thermal management, and processability.Overall, the present study demonstrates the effectiveness of a CEA-based approach for preliminary screening and down-selection of propellant formulation prior to experimental development.