The Aerospike :: physics aerospike rocket engine

When a rocket's fuel ignites, the molecules in the fuel release a tremendous amount of energy in the forms of heat, light, and sound. They expand rapidly as they move from the "throat" of the nozzle into the "bell." The compressed air inside the balloon wants to expand outward. Therefore it presses against the walls of the balloon in every direction except the place where there is no wall - the "nozzle" of the balloon. Because there is no force vector in this location, adding the vectors yields a net force to the right. A bell nozzle, where a fuel (liquid Hydrogen) mixes with an oxidizer (liquid Oxygen) at a rate "m." As they ignite they are forced into the throat, where they are compressed substantially. As they move out into the bell, they steadily expand, pushing against the nozzle and creating a net upward thrust, similar to the compressed air pushing on the walls of the balloon. Luckily, a rocket can be controlled more than a released balloon. Nozzles do not have to be bell shaped - as long as gas is expanding and pushing against a surface, creating thrust, any shape can be used! One alternative to the bell engine is the spike configuration. In particular, the Aerospike engine will be described and analyzed. The "Spike," or annular, engine is one of three basic engine designs: cones, bells, and annulars.The Cone is the simplest engine design. A cone with a narrow angle provides the greatest thrust, but a longer engine means increased weight. A short, wide-angle cone tends to be unstable under pressure (in the atmosphere). For example, the Apollo Saturn 5 featured long, relatively thin nozzles for optimum thrust at sea level. The Command Module, which operated only in space, utilized a comparatively wider engine for more expansion in space. The Bell nozzle is a compromise, opening up more rapidly near the throat and then opening more slowly near the end. However, bell nozzles are optimized for specific altitudes, therefore they will only provide their maximum thrust at a given altitude - at all other points they will provide less-than-optimum thrust. The annular, or "altitude compensating" engine is a more recently developed design. Commonly referred to as Spike engines, annulars operate with exhaust flow outside what is typically thought of as the nozzle. The exhaust flows around a central spike, rather than being contained by walls. They are called "annular" because the throat is donut-shaped, with the spike protruding from the middle.