Propellants for Rockets
Propellants for Rockets Credits - NASA
Rockets work because every action has an equal and opposite reaction (according to Sir Isaac Newton's third principle). In order for a rocket to rush forward, something has to rush backwards. That thing is the propellant. The propellant is a material that spews out of the back of the spacecraft giving it thrust, or a push forward. The most common types of propellants used for rockets are either solid fuels or liquid fuels.
Often the propellant is a kind of fuel that is burned with an oxidizer to produce large volumes of very hot gas. These gasses expand until they rush out of the back of the rocket, producing thrust. Sometimes the propellant is not burned, but pushed directly out of the spacecraft, also producing thrust. In ion propulsion, the propellant is made of electrically charged atoms, which are magnetically pushed out of the back of the spacecraft. For smaller attitude control thrusters, a compressed gas is pushed out of the spacecraft.
Rocket propellants are the fuels and the oxidizers carried by the rocket for propulsion. There are a variety of different fuels and oxidizers because some work better in particular situations or have various advantages and disadvantages.
Rocket propulsion is similar to jet propulsion with one major exception. The main difference between jet propulsion and rocket propulsion is that in rocket propulsion the oxidizer is carried with the vehicle, but in jet propulsion the oxidizer is the oxygen in the air sucked into the engine of the plane. Because there is no oxidizer in space, rockets need to carry their own oxidizers with them.
Fuels need an oxidizer to burn because burning is really a rapid chemical reaction and most fuels cannot burn by themselves. The burning that is seen and felt is the heat and the gases released from a rapid chemical reaction. The oxidizer makes that possible.