How a Rocket Engine Works

    A rocket engine is not like a conventional engine.  A conventional engine ignites fuel which then pushes on some pistons, and it turns a crank.  Therefore, it uses rotational energy to turn the wheels of the vehicle.  Electric motors also use rotational energy to turn fans, and spin disks.  A rocket engine does not use rotational energy to run.  They are reaction engines.  The principle of it is that the fuel contained within the body of the rocket goes through a chemical reaction as it comes out of the end of the rocket.  This reaction then causes thrust and propels the rocket forward.  This is an example of one of Sir Isaac Newton's fundamental laws.  "For every action, there is an equal and opposite reaction" (How Rocket Engines Work.)

This is a representation of Newton's law.

This is a picture of a space shuttle rocket engine during a test burn.
Notice the blue flame of the fuel igniting.  This cause thrust, and pushes
the rocket in the opposite direction.

    The strength of a rocket is measured in pounds of thrust.  A pound of thrust is the amount of force required to keep a one pound object stationary against gravity (How Rocket Engines Work.)  In order to generate this thrust, rockets burn one of two types of fuel, solid fuel or liquid fuel.  Because of this fact, rockets are often classified by the type of fuel that they burn.

Solid Fuel Rockets

    Solid fuel rockets are the first rockets to be recorded in history.  They were first invented in ancient China, and have been used ever since (How Rocket Engines Work.)  The chemical make up of a solid rocket fuel is very similar to the chemical makeup of gunpowder.  However, the exact chemical make up is not the same.  To make a rocket work, a fast burning nonexclusive fuel is needed.  Gunpowder explodes, making it unusable.  So the chemical composition was altered to make it burn fast, but not explode.  One of the biggest problems with solid fuel rocket engines is that once started, the reaction cannot be stopped or restarted.  This makes them considered uncontrollable.  Therefore, solid fuel rockets are more widely used for missiles, or as booster rockets.


This is a diagram of how A solid fuel rocket engine looks before and after ignition.
The solid fuel is in dark green, and then in orange as it is ignited to propel the rocket.

Liquid Fuel Rockets

    The first liquid fuel rocket was produced by Robert Goddard in 1926 (How Rocket Engines Work.)  The idea of liquid fueled rocket is easy to grasp.  A fuel and an oxidizer ,in Goddards case he used gasoline and liquid oxygen, are pumped into a combustion chamber.  A reaction takes place, and it expands propelling the rocket forward.  The expanding gas is then forced through a nozzle that makes them accelerate to a higher velocity (How Rocket Engines Work.)


This diagram is a basic model of how a liquid fuel rocket engine works.
It is easy to see that a liquid fueled rocket is much more complex that a solid fueled one.

Rocket Bodies and Nose Cones
Practical Application