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Solid-fuel Rocket Engines

Liquid Propellant Rockets

Rockets

One of the most amazing endeavors man has ever undertaken is the exploratoin of space. A big part of amazement is the complexity. Space exploration is complicated because there are so many interesting problems to solve and obstacles to overcome. Rocket engines are on the one hand so simple that you can build and fly your own model rockets very inexpensively. On the other hand, rocket engines (and their fuel systems) are so complicated that only two countries have actually ever put people in orbit.

Rocket engines are reaction engines. The basic principle driving a rocket engine is the famous Newtonian principle that "to every action there is an equal and opposite reaction". A rocket engine is throwing mass in one direction and benefiting from the reaction that occurs in the other direction as a result
A rocket engine is generally throwing mass in the form of a high-pressure gs. The engine throws the mass of gas out in one direction in order to get a reaction in the opposite direction. The mass comes from the weight of the fuel that the rocket engine burns. The burning process accelerates the mass of fuel so that it comes out of the rocket nozzle at high speed. The fact that the fuel turns from a solid or liquid into a gas when it burns does not change its mass. If you burn a pound of rocket fuel, a pound of exhaust comes out the nozzle in the form of a high-temperature, high-velocity gas. The form changes, but the mass does not. The burning process accelerates the mass.

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Photo Courtesy NASA