Rocket Fuels- Solid vs. Liquid

There are two types of rockets in use today: Solid fuel rockets, and Liquid fuel rockets. How these two types of rockets work is very different. Each have their respective advantages and disadvantages.

Solid Fuel Rockets:

The first rockets invented were solid fuel rockets. Solid fuel rockets work by burning a solid substance that burns quickly but does not explode. One such substance would be the compound containing 72% nitrate, 24% carbon and 4% sulfur. This compound is very much like gunpowder, but due to the different proportions of the materials, it burns rapidly rather than exploding. When loaded into the rocket, the fuel is shaped as a cylinder with a tube drilled down the middle. After ignition, the fuel burns along the walls of this tube, gradually consuming the fuel until there is none left (see diagram)

Solid Fuel Rocket - Before & After
Image courtesy of

In the above diagram, the fuel is in green and the tube is in blue. Once ignited, the tube is shown in orange because it is burning. In addition to a tube shaped perforation, there can be other shapes used. For example, the fuel in the space shuttles SRB's or solid Rocket boosters is often drilled with a 11 pointed star shape. This increases the surface area that is currently burning, thus increasing the resulting thrust. A common description of the fuel used in the shuttles SRB's is this:

Advantages of Solid Rocket boosters:

In spite of these advantages, there are also several disadvantages to solid rocket boosters:

To couteract these disadvantages, the Liquid fuel rocket was created.