Jet engines work by forcing air into a chamber, igniting fuel and allowing the resulting gasses escape, pushing the aircraft forwards.

But in space, there is no air.  So rockets have to bring their own fuel.

There are many types of rocket engine:

Liquid propellant

Liquid propellant rockets have two fuel parts that are pumped and mixed together and ignited.

Here are some common fuels used in rockets today:

  • Kerosene and LOX or Liquid Oxygen - oxygen which is turned into a liquid by freezing it - used in Saturn V and Russian Soyuz rockets
  • Liquid Hydrogen and LOX (Liquid Oxygen) - used in the Space Shuttle and European rockets and upper stages of Staurn V
  • Nitrogen tetroxide - used in Russian and Chinese rockets

Liquid propellants can be turned off, making them useful for control. 
Few moving parts.
Can be throttled, meaning speed can be increased or decreased.


Solid rockets are made of a chemical which burns at a reasonably constant rate.  Solid fuel was used to power the earliest form of rocket, made with black powder.

Once ignited it cannot be switched off.
They are also often unstable and can easily catch fire.

They are very powerful, hence their use.

Some common fuels used in solid rockets include:

  • Ammonium Perchlorate mixed with aluminum - used in the Space Shuttle solid rocket boosters
  • Potassium nitrate and sugar-based fuels such as dextrose or sucrose - used by amateur experimental rocket makers

Russian Soyuz rocket, first launched in 1967 is still in use today, taking astronauts and cosmonauts to the International Space Station.