Propellant trade-off analysis for upper stage solid rocket motors performance

Aim of this paper is to perform a propellant trade-off analysis in order to determine the propellant formulation able to maximize solid rocket motor performance for upper stage solid rocket motors (SRMs). The study is performed with the use of a 0D quasi-steady model of SRM internal ballistics developed on this purpose, which assumes the chemical-equilibrium in the combustion chamber up to the nozzle throat, frozen flow conditions in the nozzle divergent, and takes into account the nozzle throat erosion using a validated semi-empirical correlation of the throat recession rate. Three different upper stage SRM configurations are selected for the propellant trade-off analysis. The SRM configurations are inspired in terms of design to the available data in the open literature of three Zefiro family SRMs: Zefiro 23 and Zefiro 9A, second and third stage of VEGA launcher, and Zefiro 40, candidate for the evolution of Zefiro 23. Results indicate that, with respect to the baseline propellant HTPB 1912 (19% aluminum - 12% HTPB), a gain in the performance can be obtained for propellant formulation with a higher aluminum loading and roughly the same HTPB mass fraction. The optimum aluminum loading increases with respect to the baseline formulation for SRM configurations characterized by high nozzle throat erosion.