A propellant is a substance that produces thrust to propel an object, typically in the context of rockets or engines. It can be in the form of a gas, liquid, or solid, and works by rapidly expanding or burning to create a force that pushes against the opposite direction. Common examples of propellants include liquid oxygen and kerosene used in rocket engines, as well as solid rocket fuels. In the aerospace industry, propellants are crucial for launching spacecraft and missiles. The efficiency and performance of a propellant are measured by its specific impulse, which indicates how effectively it converts stored energy into thrust. Understanding propellants is essential for advancements in space exploration and technology, including missions to Mars and beyond.