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Composite Rubber Fuel

Composite Propellant consists of a fuel and an oxidiser. A biding agent is usually used to maintain the required shape. These binding agents are usually organic componds, of which the vast majority have been synthetic rubbers. Some high energy propellants replace the synthetic rubber binder with a double-base explosive binder. These are usually refered to as composite modified double base, or cross-linked double-base propellants.

The earliest composite rubber fuels used thiokol polysulphide rubber. This was used in early guided missiles such as the Falcon and Genie air-to-air missiles, the Nike-Hercules surface-to-air missile, and the Sergeant surface-to-surface missile. This was replaced by polybutadiene rubber in latter missiles such as the Minuteman ICBM, the Peacekeeper ICBM, the Poseidon SLBM, and the Trident SLBM.

The only significant break from the polysulphide rubber evolution is the use of polyurethane rubber fuel in the early Polaris SLBMs.

Experimentation has resulted in a large number of different rubber fuel / binders and composite rubber fuel / oxidiser combinations. Numerous rubber binder chemistry solutions are still in use today. In addition, amateur rocket enthusiasts also us rubber based composite fuels. These usually combine a polybutadiene rubber polymer with potassium nitrate (fertiliser) as an oxidiser. Sugar is often added to increase the specific impulse, in the same way that powdered aluminium is added to industry manufactured composite rubber fuel.

The following table illustrates the basic range and developmental chronology of composite and composite modified double-base propellants within the US.


Missile or booster Motor manufacturer Propellant Isp * Grain configuration Operational date
Sergeant Thiokol AP/polysulfide ca. 185 5-point star 1962
Polaris A1
Stage 1 Aerojet AP/Al/polyurethane ca. 230 6-point star 1960
Stage 2 Aerojet
AP/Al/polyurethane ca. 255 6-point star 1960
Polaris A2
Stage 2 Hercules Powder Company AP/nitrocellulose/ nitroglycerine/Al ca. 260 12-point star 1962
Polaris A3
Stage 2 Hercules Powder Company HMX/Al/AP/nitrocellulose ca. 280 slotted cylindrical center port 1964
Minuteman I
Stage 1 Thiokol AP/PBAA/Al ca. 245 6-point star 1962
Stage 2 Aerojet AP/polyurethane/Al ca. 270 4-point star 1962
Stage 3
Hercules Powder Company AP/HMX/nitrocellulose/ nitroglycerine/Al ca. 275 core and slotted tube- modified end burner 1962
Titan 3 solid- rocket motor United Technology Corporation AP/PBAN/Al ca. 265 8-point star and circular perforations 1965
Space Shuttle SRB Thiokol AP/PBAN/Al ca. 245 11-point star and tapered perforations