Rocket propellants are substances used to produce thrust in rockets. They can be classified into two main types: liquid propellants and solid propellants. Liquid propellants, such as liquid oxygen and kerosene, are stored in separate tanks and mixed before combustion. Solid propellants, on the other hand, are pre-mixed and packed into a solid form, making them simpler to handle. The choice of propellant affects a rocket's performance, efficiency, and mission capabilities. For example, NASA often uses liquid hydrogen and liquid oxygen for their Space Launch System due to their high energy output. Understanding rocket propellants is essential for designing effective space missions.