This is are hybrid rocket engines designed and built by one of my customers and friends, Dan Moser from Compositex. About Hybrid Rockets A hybrid rocket is one that uses a solid fuel, usually some type of rubber or plastic, and a liquid oxidizer, such as liquid oxygen or hydrogen peroxide. The fuel is most often shaped into a cylinder with a hole down the middle through which the oxidizer passes or with special geometry shapes to increase the surface area. The fuel is vaporized and burns with the oxidizer, the products of which pass through a De Laval rocket nozzle, thereby producing thrust. Hybrid rockets are more reliable than their liquid counterparts (partially due a significant reduction in the number of moving parts) and they can't experience a "hard" or explosive start like is the case of the bi-propellant rockets in case the fuel and oxidizer are not ignited on time. Unlike solid rocket motors, hybrid rocket motors are not explosive by nature. Also unlike solids, hybrids can be shutdown and restarted, and they can be throttled, though not to the degree generally available with a liquid mono-propellant rocket motors. Almost all the hydrogen peroxide monopropellant rockets can be converted to a hybrid rocket by the addition of a solid fuel charge in the combustion chamber, this increases the ISP a lot and is significantly less costly that liquid bi-propellant rockets. In the hydrogen peroxide hybrid rockets you don't need a igniter because the temperature of the reaction ignites the solid fuel. The most popular solid fuel used with hydrogen peroxide hybrid rocket engine is polyethylene or polymethylmetacrylate, also both have ablative cooling caracteristics on the nozzle.