Rocket fuels are substances that provide the energy needed to propel rockets into space. They can be classified into two main types: liquid fuels and solid fuels. Liquid fuels, like liquid oxygen and kerosene, are stored in separate tanks and mixed before combustion. Solid fuels, on the other hand, are pre-mixed and packed into a solid form, making them simpler to handle. The choice of rocket fuel affects the rocket's performance and efficiency. For example, NASA often uses hydrogen and oxygen in its space missions due to their high energy output. Understanding rocket fuels is essential for designing effective space vehicles.