SolidFuel

A solid propellant is a monopropellant fuel-a single mixture of several chemicals (the oxidizing agent and the reducing agent or fuel). This fuel, as implied, is in its solid state and has a preformed or molded shape. The propellant grain, this interior shape of the core is an important factor in determining a rocket's performance. The variables determining grain-relative performance are core surface area and specific impulse. The composite solid propellant for rocket motors of ISRO uses ammonium perchlorate (oxidiser), fine aluminium powder (fuel) and hydroxyl terminated polybutadiene (binder).

The solid motors produced in ISRO include those for the first stage booster motor of the Polar Satellite Launch Vehicle (PSLV) - a five segmented motor of 2.8 m diameter and 22 m length, weighing 160 tons with a thrust level of 450 tons. Pitch and yaw control of the PSLV during the thrust phase of the solid motor is achieved by injection of an aqueous solution of strontium perchlorate in the nozzle to constitute Secondary Injection Thrust Vector Control System (SITVC). The shuttle's reusable solid rocket motor is the largest solid rocket motor ever flown, the only one rated for human flight and the first designed for reuse. Each shuttle launch requires the boost of two reusable solid rocket motors to lift the 4.5-million-pound shuttle vehicle.During space shuttle flights, solid rocket motors provide 80 percent of the thrust during the first two minutes of flight. Each motor generates an average thrust of 2.6 million pounds and is just over 126 feet long and 12 feet in diameter. It is the primary component of the shuttle's twin solid rocket boosters.During a shuttle launch, the solid propellant rockets take the shuttle to an altitude of 28 miles at a speed of 3,094 mph before they separate and fall into the ocean to be retrieved, then refurbished and prepared for another flight. The Ariane 5 launcher is fitted with two P230 boosters, each 30 m high and containing 237 t of propellant grain in three segments. Each booster has a thrust of 540 t, equal to that of the most powerful Ariane 4 (the Ariane 44l version), which makes it the most powerful booster ever built in Europe.It also uses a new binder For space shuttle solid rocket boosters or SRB sthe propellant mixture in each SRB motor consists of an ammonium perchlorate (oxidizer, 69.6 percent by weight), aluminum (fuel, ,16 percent), iron oxide (a catalyst, 0.4 percent), a polymer (a binder that holds the mixture together, 12.04 percent), and an epoxy curing agent (1.96 percent). The propellant is an 11-point star- shaped perforation in the forward motor segment and a double- truncated- cone perforation in each of the aft segments and aft closure. This configuration provides high thrust at ignition and then reduces the thrust by approximately a third 50 seconds after lift-off to prevent overstressing the vehicle during maximum dynamic pressure. Surface area is the amount of propellant exposed to interior combustion flames, existing in a direct relationship with thrust. An increase in surface area will increase thrust but will reduce burn-time since the propellant is being consumed at an accelerated rate. The optimal thrust is typically a constant one, which can be achieved by maintaining a constant surface area throughout the burn. Examples of constant surface area grain designs include: end burning, internal-core and outer-core burning, and internal star core burning (figure 3). Various shapes are used for the optimization of grain-thrust relationships since some rockets may require an initially high thrust component for takeoff while a lower thrust will suffice its post-launch regressive thrust requirements. Such a compromise has implications as seen, but it optimizes overall rocket performance. Complicated grain core patterns, in controlling the exposed surface area of the rocket's fuel, often have parts coated with a non-flammable plastic (such as cellulose acetate). This coat prevents internal combustion flames from igniting that portion of fuel, ignited only later when the burn reaches the fuel directly. Specific Impulse, the thrust per unit propellant burned each second, measures rocket performance and more specifically, internal thrust production a product of pressure and heat. Thrust in chemical rockets (inclusive of both solid and liquid fueled rockets, is a product of the hot and expanding gasses created in the combustion of an explosive fuel (a reduction-oxidation reaction). The degree of the fuel's explosive power coupled with the rate of combustion is the specific impulse. In designing the rocket's propellant grain specific impulse must be taken into account since it can be the difference betwixt a conflagration of failure (explosion), and a successfully optimized thrust producing rocket. If a propellant with a high specific impulse is used as the fuel for a rocket whose grain design offers a high surface area ratio, high amounts of thrust will ensue ignition. And if the engine grain casing cannot withstand the extreme pressure and temperature it will rupture and explode. Thus, the function involving the variables of both specific impulse and surface area must be considered in grain design. The departure from the use of gunpowder to more powerful fuels (higher specific impulses) marks the development of modern solid fueled rockets. Once the chemistry behind rocket fuels (fuels provide their own "air" to burn) was discovered, scientists sought the evermore-powerful fuel, constantly approaching new limits. A composite propellant is a mechanically mixed combination of the oxidizer and the fuel. Some common solid oxidizers are: ammonium perchlorate (NH4-ClO4) and ammonium nitrate (NH4-KNO3), chemicals providing far more oxygen than potassium nitrate (KNO3), the oxidizing agent in gunpowder. These oxidizers are often mixed, in making composite propellants, with synthetic rubbers such as: polystyrenes, polysulfides, and polyurethanes. Another type of propellant is homogeneous where the oxidizer and the fuel are combined as one molecule. Propellants of this type often use a double-base (combination of two propellants) of nitrocellulose and nitroglycerin (C3H5(ONO2)3). Advantages/Disadvantages: Solid fueled rockets are relatively simple rockets. This is their chief advantage, but it also has its drawbacks. Once a solid rocket is ignited it will consume the entirety of its fuel, without any option for shutoff or thrust adjustment. Another key disadvantage is the danger involved in the premixed fuels of monopropellant rockets. In the double-base homogeneous nitrocellulose-nitroglycerin propellant, for example the nitroglycerin is too unstable (sufficient shock will detonate) to use individually add thus a more stable propellant like nitrocellulose (a form of gunpowder) is added. Composite engines, having the fuel and oxidizer as separately mixed elements, are less sensitive to shock and therefore safer to use. A relatively low specific impulse limits the use of solid rockets when large amounts of thrust precondition. The Saturn V moon rocket used nearly 8 million pounds of thrust that would not have been feasible with the use of solid propellant, requiring a high specific impulse liquid propellant. The ease of storage of solid propellant rockets is another main advantage employing a high level use in the military. Some of these rockets are small missiles such as Honest John and Nike Hercules; others are large ballistic missiles such as Polaris, Sergeant, and Vanguard. Liquid propellants may offer better performance, but the difficulties in propellant storage and handling of liquids near absolute zero (0 degrees Kelvin) has limited their use unable to meet the stringent demands the military requires of its firepower.