A solid rocket motor utilizes an internal propellant grain cast inside a high-strength pressure casing. When ignited, combustion regresses perpendicular to the exposed propellant surface area (A_b) according to Saint-Robert's empirical burn rate law. Internal chamber pressure reaches a steady-state equilibrium when the mass burning rate from the propellant grain matches the choked sonic mass discharge capacity through the convergent-divergent nozzle throat.