Solid Fuel Rocket

Overview

Solid Fuel Rocket/ Solid Rocket is a rocket with a Rocket engine that uses a Solid propellant (Solid Fuel/Solid Oxidiser). The earlier Rockets used solid fuel in the form of gun powder. Most of the Rockets even today uses solid fuel in powder form to function. Liquid Rockets seem more reliable and efficient nowadays, that's the reason why Solid fuel rockets have by replaced by liquid fuel and other rockets.

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What is a Solid Rocket Motor ?

In a solid-rocket motor, the propellant consists of one or more pieces mounted directly in the motor case, which serves both as a propellant tank and combustion chamber. The propellant is usually arranged to protect the motor case from heating. Most modern propellant charges are formed by pouring a viscous mix into the motor case with suitable mold fixtures. The propellant undergoes solidification and then the mold fixtures are removed, leaving the propellant bonded to the motor case with a suitably shaped perforation down the middle. During operation the solid burns on the exposed inner surfaces. These burn away at a predictable rate to give the desired thrust.

The motor case is made up of steel or aluminum tubes. It has a head-end dome that contains an igniter and an aft-end dome that houses or supports the nozzle. The motor case has got insulation on their interior surfaces, especially those not covered by propellant, for protection against thermal failure during the burn.

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Ae

m

nozzel

Ve

pe

throat

exit - e

po

exhaust

V = Velocity

m = mass flow rate

p = pressure

Thrust = F = mVe + (pe - po)Ae

Where is it Used ?

Solid Fuel Rocket are used in air to air and air to ground missiles, in model rockets. Also, widely as boosters in satellite launchers. 

How does the Engine work ?

In Solid Fuel Rocket, fuel and oxidizer is mixed together into solid propellant and are packed into a cylinder. A hole is made into the cylinder which acts as a combustion chamber. When the mixture is ignited, combustion takes place on the surface of the propellant. A flame front is generated which burns into a mixture. The combustion produces a great number of exhaust gases at high temperatures and high pressure. The amount of exhaust gases produces depends upon the area of the flame front and engine designers use a variety of hole shapes to control the amount of thrust for a particular engine. The hot exhaust gas is passed through the nozzle which accelerates the flow. Rocket thrust is produced as per Newton's third law of motion which states, " For every action, there is an equal and opposite Reaction "

The amount of thrust released by the rocket engine is determined by the design of the nozzle. The smallest cross-sectional area of the nozzle is called the throat of the nozzle. The hot exhaust gas is restricted at the throat of the nozzle. The Mach number in the throat and mass flow rate 'm' are determined by the throat area. The area ratio from the throat to the exit Ae fixes the exit velocity Ve and the exit pressure pe. If the free stream pressure is given by p0, the thrust F equation becomes :

F = mVe + (pe - po)Ae

There is no free stream mass times free stream velocity term in the thrust equation because no external air is brought on board. Here the oxidizer is mixed into the propellant, therefore the solid rockets can generate thrust in a vacuum where there is no other source of oxygen. That's why a rocket will work in space, where there is no surrounding air, whereas a gas turbine or propeller will not work. Turbine engines and propellers rely on the atmosphere to provide the oxygen for combustion and as the working fluid in the generation of thrust.

Different Propellants Used

Propellants for solid-rocket motors are made from a wide variety of substances, selected for low cost, acceptable safety, and high performance. The selection is strongly affected by the specific application. Typical ingredients are ammonium perchlorate (a granular oxidizer), powdered aluminum (a fuel), and hydroxyl-terminated polybutadiene, or HTPB (a fuel that is liquid during mixing and that polymerizes to a rubbery binder during curing). This combination is used in major space boosters. Higher performance is achieved by the use of more energetic oxidizers (e.g., cyclotetramethylene tetranitramine [HMX]) and by energetic plasticizers in the binder or by energetic binders such as a nitrocellulose–nitroglycerin system.