Modular rocket motors and methods of making modular rocket motors

1 . A 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.

2 . The modular rocket motor of claim 1 , wherein the radial retention interface comprises a polar boss, and a forward polar boss enclosure.

3 . The modular rocket motor of claim 2 , wherein the radial retention interface is formed by molding the polar boss using boss molding material.

4 . The modular rocket motor of claim 2 , wherein the polar boss is wound into the cylindrical composite case, allowing the cylindrical composite case to expand in response to pressure increases during ignition and burn.

5 . The modular rocket motor of claim 3 , wherein the boss molding material comprises a molding compound.

6 . The modular rocket motor of claim 5 , wherein the polar boss is centered in the cylindrical composite case.

7 . The modular rocket motor of claim 3 , wherein the polar boss comprises the plurality of radial tabs, the plurality of radial tabs comprising at least six radial tabs.

8 . The modular rocket motor of claim 5 , wherein the cylindrical composite case comprises the forward cartridge, the forward cartridge comprises a composite case material, and wherein the composite case material comprises vinyl ester.

9 . The modular rocket motor of claim 5 , wherein the cylindrical composite case comprises the forward cartridge, the forward cartridge comprises a composite case material, and wherein the modular rocket motor further comprises es a central joint and an aft joint.

10 . The modular rocket motor of claim 9 , wherein the gas gap is vented to a central combustion chamber.

11 . 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.

12 . The method of claim 11 , further comprising curing the cartridges under pressure and temperature.

13 . The method of claim 12 , wherein curing occurs at a temperature of at least 284 F.

14 . The method of claim 13 , further comprising trimming a closure of the cartridges such that adjacent cartridges overlap in fitted engagement.

15 . The method of claim 14 , wherein said mold comprises aluminum.

16 . The method of claim 15 , further comprising making a plurality of holes proximate to the closure for a plurality of joints, the plurality of joints securing the adjacent cartridges in fitted engagement.

17 . The method of claim 16 , wherein the plurality of joints are secured in fitted engagement with steel pins that epoxy into machined grooves of the cartridges.

18 . The method of claim 17 , the method further comprising adding EPDM to the closure inner diameter for an enhanced heat seal.

19 . 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.