How does grain geometry affect solid rocket motor performance?

Grain geometry determines burn area evolution and thus thrust profile. Common configurations: Star/wagon wheel (progressive or neutral burn, high volumetric loading), End burner (regressive, low thrust long duration), Cylindrical bore (progressive, simple), and Finocyl (neutral, complex). Progressive burns produce increasing thrust, regressive decreasing, neutral constant. Design considerations: Desired thrust profile for mission, Structural integrity under pressure/acceleration, Propellant loading efficiency (85-95% volumetric), Burn surface web thickness for total impulse, and Erosive burning at high port velocities. Analysis uses burning rate law (r = a*Pc^n) and geometry evolution models. Testing validates performance predictions.