Rocket Fuels

When fuel burns, it combines with oxygen in the air. Without oxygen, fuel will not burn. Rockets have to function in space, where there is no air to supply oxygen, and so they carry their own supply of oxygen-or a chemical that contains oxygen, called the oxidizer – for burning the fuel. The fuel and the oxidizer also are called propellants.

Rockets can use kerosene fuel, just as aircraft do. The rocket fuel RP-1 is kerosene. The first stage of the giant Saturn V rocket that launched astro­nauts to the Moon during Project Apollo burned RP-1.

Hydrogen is another popular rocket fuel. The Space Shuttle’s main engines burn hydrogen and oxygen from an external tank. Hydrogen and oxygen are normally gases, but the tanks needed to carry enough of these gases to launch a heavy rocket into space would be gigantic. Hydrogen and oxygen, there­fore, are cooled and compressed until

TYPES OF FUEL

Every fuel has a flash point. The flash point is the lowest temperature at which a fuel can be set on fire by a spark or flame. A fuel with a low flash point catches fire more easily than a fuel with a high flash point. Avgas has a lower flash point than jet fuel.

they change to liquids, which take up much less space. Hydrogen has to be cooled to -423°F (-253°C). Oxygen has to be cooled to -298°F (-183°C). Super­cold propellants such as these are known as cryogenic propellants.

There are some chemicals that burst into flames as soon as they meet. They are useful as rocket propellants because they do not need a spark or flame to start them burning. Propellants of this type are called hypergolic propellants. Turning off the supply of hypergolic propellants stops a rocket from working. Turning them on makes the rocket fire again. Hypergolic propellants are used by small rockets that have to start and stop frequently, such as those that help the Space Shuttle maneuver in space.

O A solid rocket booster is maneuvered into place on a Delta II rocket that is being prepared for launch by NASA at Cape Canaveral Air Force Station in Florida.

The simplest rockets burn solid fuel, like giant fireworks. The fuel and oxidizer are mixed while liquid and then poured into the rocket, where they set hard. To fire a solid fuel rocket, a flame is sent down a hole through the middle of the rocket. Once a solid fuel rocket starts firing, it keeps going until all the propellant is used up. Small solid rockets are often strapped to the side of a bigger rocket to supply extra thrust for takeoff. The biggest solid fuel rockets ever built are the two solid rocket boost­ers (SRBs) that help to launch the Space Shuttle.