Modular rocket motors and methods of making modular rocket motors

A method of making a modular rocket motor, the modular rocket motor comprising:

• a. a cylindrical composite case, the cylindrical composite case having a forward end and an aft end, the aft end having a nozzle;
• b. a plurality of cartridges suspended inside the cylindrical composite case;
• c. wherein the cartridges house a propellant;
• d. wherein the cartridges are retained co-axially with the cylindrical composite case;
• e. wherein said forward end comprises the forward cartridge, the forward cartridge comprising a radial retention interface comprising a plurality of radial tabs;
• f. wherein the aft end comprises the aft cartridge;
• g. wherein a gas gap is formed between the cartridges and the cylindrical composite case;
• and
• h. wherein the gas gap permits the cylindrical composite case to swell both radially and axially during ignition and burn, the method comprising the steps of:
• a. fabricating a mandrel that supports a cure temperature of at least 300 F;
• b. fabricating a mold for a charging gap;
• c. Molding a polar boss using boss molding material with minor machining, wherein the polar boss comprises the plurality of radial tabs;
• d. Curing ethylene propylene diene monomer (EPDM) to a face of the polar boss to form a polar boss pre-mold;
• e. adding the polar boss to the mandrel and lying up EPDM sheets over a forward cartridge resin;
• f. laying up dry fabric over the forward cartridge resin;
• and
• g. applying a vacuum bag and infusing resin on the cylindrical composite case.

A method of making a forward cartridge of a modular rocket motor, the modular rocket motor comprising:

• a. a cylindrical composite case, the cylindrical composite case having a forward end and an aft end, the aft end having a nozzle;
• b. a plurality of cartridges, including the forward cartridge, suspended inside the cylindrical composite case;
• c. wherein the cartridges house a propellant;
• d. wherein the cartridges are retained co-axially with the cylindrical composite case;
• e. wherein said forward end comprises the forward cartridge, the forward cartridge comprising a radial retention interface comprising a plurality of radial tabs;
• f. wherein the aft end comprises the aft cartridge;
• g. wherein a gas gap is formed between the cartridges and the cylindrical composite case;
• and
• h. wherein the gas gap permits the cylindrical composite case to swell both radially and axially during ignition and burn, the method comprising the steps of:
• a. laying up fiberglass fabric sheet over uncured ethylene propylene diene monomer (EPDM) to form EPDM sheets;
• b. laying the EPDM sheets over a mandrel;
• c. laying fiberglass pre-peg sheets over the mandrel;
• d. curing the pre-preg sheets, wherein the pre-preg sheets are defined by a pre-preg thickness;
• e. fabricating a vinyl ester forward cartridge resin using an infusion process;
• f. reinforcing the vinyl ester with a molding compound;
• g. forming the radial retention interface, wherein the radial retention interface comprises a polar boss, a forward polar boss enclosure;
• h. molding the polar boss using boss molding material with minor machining, wherein the polar boss is molded into the plurality of radial tabs, the plurality of radial tabs including at least six radial tabs;
• and
• i. where the plurality of radial tabs are located on the forward cartridge.