Abstract: The main subjects of the present invention are: a process for obtaining a solid composite propellant (with a polyurethane binder filled with ammonium perchlorate and with aluminum): characteristically, the ammonium perchlorate charge of said propellant is obtained from at least two charges each having a specific monomodal particle size distribution. It is thus sought to reduce the thrust oscillations and the alumina deposits at the back of the engine; a solid composite propellant, the solid propellant charges and the associated rocket engines.