Rocket propulsion systems are mechanisms that generate thrust to propel rockets into space. They work by expelling mass in the opposite direction, following Newton's third law of motion, which states that for every action, there is an equal and opposite reaction. These systems typically use either liquid or solid propellants to produce high-speed exhaust gases. Liquid propulsion systems, like those used in the Space Shuttle, allow for adjustable thrust and can be shut down if necessary. In contrast, solid propulsion systems, often found in military missiles, provide a simpler design but lack the ability to control thrust once ignited. Both types are essential for space exploration and satellite deployment.