Ammonium perchlorate composite propellant

Ammonium Perchlorate Composite Propellant, or APCP, is a rocket fuel composed of Ammonium perchlorate (AP), an elastomer binder such as Hydroxyl-terminated polybutadiene (HTPB) or Polybutadiene Acrylic Acid Acrylonitrile Prepolymer (PBAN), small amounts of powdered aluminum, and various catalysts. The AP serves as the oxidizer, while the binder and aluminum serve as the fuel. Burn rate catalysts determine how quickly the mixture burns. This fuel, which is rubbery in consistency, is used in high-power model rocketry, and in larger applications such as military weapons and space exploration vehicles.

Commercial APCP rocket engines usually come in the form of reloadable motor systems, which require the rocketeer to assemble the motor prior to use. The APCP itself comes in long cylinders which are loaded into the reusable motor casing, which is machined from aluminum.

Black powder is another model rocket propellant, which is used in lower power rocket engines because of its cheaper nature. Compacted black powder slugs become too fragile as the size and power of rocket engines increase. APCP's rubbery nature makes it ideal for larger engines, not only because it is almost three times as powerful as black powder by weight, but also because it does not crack like black powder slugs would if subjected to accidental shock. Such cracks in black powder engines can cause the engine to fail catastrophically, destroying the rocket and placing the spectators and rocketeer in danger.

Commercial model APCP engine manufacturers produce different propellant formulations that create different performance and visual effects. For example, in the same reloadable motor casing, one can purchase a propellant that produces dense black smoke and less power, or a laser-red flame with white smoke and more power.