5. Rocket Propellant

Rocket Propellant

* The propellants are chemical substances which on ignition provide thrust for the rocket to move forward. These substances are called rocket propellants.

(1) Types of rocket propellants : Depending upon the physical state, propellants  can be classified as.

(i) Solid propellants : The  solid propellants are mixtures of solid fuel and solid oxidiser. These are further divided into to classes.

(a) Composite propellants

(b) Double base propellants

(ii) Liquid propellants : These consist of an oxidizer such as liquid oxygen, nitrogen tetroxide (N₂O₄) or nitric acid and a fuel such as kerosene, alcohol, hydrazine or liquid hydrogen. These are further classified as,

(a) Monopropellants 

(b) Bipropellants

Advantages of Biliquid Propellants over Solid Propellants

The  biliquid propellants give higher thrust than solid propellants.

The thrust generated by liquid propellants can be controlled by switching on and off the flow of propellants. On the other hand, the thrust cannot be controlled in solid propellants.

(iii) Hybrid propellants : These are the propellants which consist of solid fuel and a liquid oxidiser. For
example, liquid  N₂O₄ (liquid oxidiser) and acrylic rubber (solid fuel).

(2) Examples of Propellants used in Different Rockets

(i) Saturn booster rocket of American space programme used a mixture of kerosene and liquid oxygen as the propellant in the initial stage where as liquid oxygen and liquid hydrogen were used as propellant in high altitudes.

(ii) Russian rockets such as Proton used a liquid propellent consisting of kerosene and liquid oxygen.

(iii) The Indian satellites SLV-3 and ASLV used composite solid propellants.

(iv) The rocket PLSV will use solid propellant in the first and third stages and liquid propellant in second and fourth stages. The liquid propellant will consist of N₂O₄ and unsymmetrical dimethyl hydrazine (UDMH) and N₂O₄ and monomethyl hydrazine (MMH) respectively.