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Whats the difference between liquid fuel and solid fuel rockets?
Liquid fuel and solid fuel are used at different times of a spacecrafts flight because of their different qualities. Solid fuel is cheaper than liquid fuel but it cannot be controlled as well. When a rocket launches from Earth it uses solid rocket boosters with solid fuel to gain enough thrust to leave the atmosphere. Liquid fuel often involves a mixture of liquid hydrogen and liquid oxygen. It is different than solid fuel in that it can be controlled, or throttled. But it also is more complicated and requires extra weight on the spacecraft (it needs more "stuff" like piping and pumps). You can see a picture of both types of fuel here. You can read about liquid and solid fueled rockets here.