Method of manufacturing multi-layered propellant grains

A method of manufacturing a multi-layered propellant grain comprising the following steps:

• providing a first propellant formulation in the form of a paste;
• providing a die configured to produce a structure having an outer shell and a hollow interior when the first propellant formulation is extruded therethrough;
• extruding the first propellant formulation through said die using a ram press or screw extruder, to produce a first propellant layer having the outer shell defining the hollow interior in the form of a passageway having open ends;
• providing a second propellant formulation, said second propellant formulation being of low viscosity, wherein an as-extruded viscosity of the first propellant formulation exceeds said low viscosity, and wherein said second propellant formulation is of low viscosity such that it has an as-extruded viscosity of from 0.1 to 200 pascal·seconds and is in the form of a liquid or a gel;
• injecting said second propellant formulation into said passageway defined by said first propellant layer to form a second propellant layer disposed in said passageway, wherein the injecting of said second propellant formulation is performed such that the second propellant layer comprises a perforation in the center of the second propellant layer, wherein the second propellant formulation has said low viscosity immediately following injection into said passageway, wherein said injecting of said second propellant formulation is performed at the same time as the said extruding of said first propellant formulation and is performed through a pressure differential means selected from the group consisting of:
• pumps and pressurized vessels, wherein the pressure differential means requires less power and is smaller in size as compared to the ram press or screw extruder;
• and
• after the step of injecting, hardening said second propellant layer such that said second propellant layer achieves a viscosity that is greater than said low viscosity, said greater viscosity being sufficient to prevent flowing of the second propellant layer within said passageway,
• wherein the first and second propellant layers have different rates of burning.