different forms of rockets

        Types of rockets

     

         From early invention of rockets to the present rockets there took a lot of changes in its construction, production and application and many different types of rockets took birth in this course.

       

        Generally these rockets are distinguished according to the type of engine they include and the type of engine, depend on their propellant. The early rockets are of liquid propellants, slowly the solid, the hybrid came into existence. Electric and nuclear propellants are the modern ones. Anyhow liquid propellants are most commonly used for the reasons we discuss later.

        

             Before getting into deep, let us know what is a propellant meant by? Ahh  it`s like the fuel for any other vehicles. In the case of liquid and solid propulsion, the propellants are generally chemicals, Ions or charged particles in electric propulsion. Now I guess we can move with the types of propellants.

 Liquid propellants

  

        Propellants in liquid state that consists fuel and oxidizer for combustion. The most commonly used liquid propellants are liquid hydrogen as fuel and liquid oxygen as oxidizer. We select the propellants that on combustion release maximum energy. Ignition is required for some of the propellants which are called Non-Hypergolic and the combination of propellants that doesn`t need any ignition are the HYPERGOLIC ones. The engine contains a fuel tank and an oxidizer tank filled with respective contents. They both are combined in a chamber and then ignited, resulting the combustion and then the gases are ejected out through nozzle with very high exhaust velocities. 

                                               

          To increase the exhaust velocities, the propellants are either pumped out or maintained at very high pressures. The other alternate is to maintain the propellants at very low temperatures to increase their specific densities (such a low temp. where the gases turn to liquid forms which is our sole aim) and then pumped into combustion chamber. The temperatures where these gases turn to liquid form are called the cryogenic temperatures and the engine using this process is called CRYOGENIC engine. We discuss about these cryogenic engines in later steps.

Solid propellants

               As the name states, propellants in solid state are solid propellants. These are generally used for booster rockets. The construction, arrangement and combustion process in it, differs completely with the liquid propellant rockets. Consists a single propellant, made in the form of small blocks called GRAINS and are arranged in highly mannered pattern in a chamber. The ignition starts from one end and slowly spreads to every grain. Higher the surface area, faster the combustion and faster the combustion, larger the thrust. Thus there are many patterns proposed for better results.

              Nitrocellulose, Nitroglycerine and nitramine products are the most common solid propellants. The above chemicals with some additives combine to form the grains. Gas released after the combustion is no2 which is very helpful in increasing the exhaust velocities and the thrust.

Hybrid propellants  

               When fuel and oxidizer are in different phases then it is referred to as hybrid propellant. It generally comprises of liquid oxidizer and solid fuel. In most cases the fuel taken is a polymer. The liquid oxidizer could be liquid O2, liquid HNO3 or liquid N2O4. We avoid using liquid fluorine due to its high reactivity and unstability.

Electric propellants

              In this, the propellants used are either ions or charged particles. Using high voltages and plasma content the rockets are propelled. Inert gases support a lot for this system and among them xenon works better and almost all the electric propulsion systems generally uses xenon as their propellant. Due to its low thrust production, these are not used for rocket launching into the orbit but they are used for satellite propulsion for adjusting their orbits.

Nuclear propellants

   We generally use hydrogen as the propellant due to its low molecular mass. The gas is heated in a nuclear reactor to very high temperatures and then expanded in a nozzle to generate thrust. Alternatively nuclear rocket is used to generate electricity to power electric rockets.

It`s all about the past and the present, who knows what`s going to be in future?