Rocket propellant or rocket fuel means fuel for rockets. It may be in the form of solid, liquid or gas. Most rockets are chemical rockets propelled by fire. Most chemical rockets use two propellants: a fuel and an oxidizer. These two chemicals are sometimes mixed, and sometimes kept in separate containers. The Space Shuttle had solid fuel boosters with powdered aluminium as fuel and ammonium perchlorate as oxidant. The Space Shuttle main engines used liquid hydrogen as fuel and liquid oxygen as oxidant. A toy water rocket uses a gas, such as compressed air, as a propellant. References