Rocket Propellants and their characteristicsIntroductionRocket propellants are the fuels and the oxidizers carried by the rocket for propulsion. Itis the mass that is stored in some form of propellant tank, prior to being used as the propulsive mass that is ejected from a rocket engine in the form of a fluid jet to producethrust. A fuel propellant is often burned with an oxidizer propellant to produce largevolumes of very hot gas. There are a variety of different fuels and oxidizers because theyall have some tradeoffs. For example, the cryogenic propellants have a better specificimpulse but they are harder to handle and tend to have low densities. A higher specificimpulse helps by increasing the efficiency of the thrust per amount fuel spent. However there is a tradeoff in terms of difficulty in handling and the low densities which require alarger tank Chemical rocket propellants are most commonly used, which undergoexothermicchemical reactionsto produce hot gas used by arocketfor propulsive purposes. There are three main types of propellants: solid, liquid, and hybrid.Main Properties of Rocket propellantsRocket propellants possess unique properties, such as a capability to self-sustain the burning process, generate thermal energy, and simultaneously produce propulsive mass.Some types of propellants are even able to self-ignite (initiate burning without outside power input). Unlike most other combustible chemicals, rocket propellants can burn invacuum. This is because a propellant consists of two integral components: a fuel that burns and produces propulsive mass and an oxidizer that facilitates and sustainsoxidation. In this respect, rocket propellants are more like explosives rather than likeautomobile and aviation fuels which require atmospheric air for oxidation.The major difference between explosives and rocket propellants is the gas expansion ratewhich is much slower in propellants and makes it possible to contain and control the process of burning inside the rocket engine.The gases produced when a fuel propellant is burned, expand and push on a nozzle,which accelerates them until they rush out of the back of therocketat extremely highspeed, making thrust. Sometimes the propellant is not burned, but can be externallyheated for more performance. For smaller attitude controlthrusters, a compressed gasescapes the spacecraft through a propelling nozzle.Inion propulsion, the propellant is made of electrically charged atoms (ions
), which areelectromagneticallypushed out of the back of the spacecraft. Magnetically acceleratedion drives are not usually considered to be rockets however, but a similar class of thrusters use electrical heating and magnetic nozzles. Burning is the chemical process of decomposition and oxidation of the propellant. The resulting highly heated andcompressed gas (propulsive mass) is ejected from a combustion chamber and facilitates
propulsion—movement of the aggregate attached to the rocket engine. In physical terms,combustion converts chemical energy into kinetic energy.How do rocket propellants help in rocket propulsion?Rockets create thrust by expellingmass backwards in a high speed jet, making use of Newton's Third Law
of motion. Chemical rockets create thrust by reacting propellantswithin a combustion chamber into a very hotgasat high pressure, which is then expandedand accelerated by passage through a nozzle at the rear of the rocket. The amount of theresulting forward force, known as thrust, that is produced is themass flow rateof the propellants multiplied by their exhaust velocity (relative to the rocket), as specified by Newton's third law of motion.Thrust is therefore the equal and opposite reaction that moves the rocket, and not byinteraction of the exhaust stream with air around the rocket. Equivalently, one can think of a rocket being accelerated upwards by the pressure of the combusting gases against thecombustion chamber and nozzle.This...
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