In this method of propulsion techniques, propellants used are basically chemicals, which produces high amount of energy on burning.
Depending upon the physical state of the propellant used they can be classified as:
a) Propulsion using solid propellants: -
When the solid fuel is ignited, it burns along the walls of the combustion chamber. As discussed earlier, solid fuels have perforation. This is to increase the surface area and eventually to increase the thrust produced by the rocket. As the combustion proceeds, the perforation shape changes into a circle. This provides high thrust initially and thrust lowers during the middle of the flight.
Solid-fuel rocket engines have three important advantages:
They also have two disadvantages:
b) Propulsion using liquid propellants: – liquid propellants (see liquid propellants) are used to propel the rockets.
In liquid propellant rockets, fuel and oxidizer are pumped into the combustion chamber. They are ignited to produce high pressure, high velocity gases. These gases are then directed towards the nozzle to provide thrust to the rocket.
Liquid propellant rockets encounter a problem in cooling the combustion chamber and nozzle. For this purpose, cryogenic fuels (super cooled liquids) are circulated to cool these parts.
The next propulsion technique is nuclear propulsion.