They can be in solid or liquid state and there are even some hybrid fuel engines.
Most people have seen the launching of a spacecraft or rocket by some video transmission. Around there can be multiple questions, for example, do they use the same fuel as a truck or a vehicle?
The answer is no, because it is designed to perform other functions, therefore, it needs a different machinery and that requires much more power.
What fuel do they use?
So far, most space missions have used jet engines, known as rocket motors, which operate by ejecting gases, which they store in the combustion chamber, into the atmosphere.
In general, these are hydrogen and oxygen, which function as fuel and oxidant to propel the ship. They can be in solid or liquid state, and there are even some hybrid fuel engines.
For years, plutonium-238 – a radioactive isotope that does not exist in nature and is obtained by bombarding other isotopes? It has been used for space missions, because the heat produced by its decomposition is used to generate electrical energy. The drawback of this compound is that it is scarce and expensive to produce.