Simple Parametric Relations for Solid Rocket Stage Inert Mass Estimation

This study quantifies the relationship between propellant mass and inert mass for solid rocket stages with steel and composite casings. Regression models reveal that steel-cased stages exhibit sub-linear scaling due to structural overhead, while composite-cased stages show lower inert mass and near-linear scaling, partly reflecting modern design improvements. Statistical analysis highlights substantial variability arising from stage-specific design choices, safety factors, and subsystem configurations. The results provide practical guidance for preliminary design, including conservative upper-bound estimates for inert mass and insights into the influence of casing material and stage design.