Rockets Engines
A rocket engine is a type of jet engine that uses only stored rocket propellant mass for forming its high-speed propulsive jet. Rocket engines are reaction engines, obtaining thrust in accordance with Newton's third law. Most rocket engines are internal combustion engines, although non-combusting forms (such as cold gas thrusters) also exist. Vehicles propelled by rocket engines are commonly called rockets. Since they need no external material to form their jet, rocket engines can perform in a vacuum and thus can be used to propel spacecraft and ballistic missiles.
Compared to other types of jet engines, rocket engines are by far the lightest, and have the highest thrust, but are the least propellant-efficient (they have the lowest specific impulse). The ideal exhaust is hydrogen, the lightest of all gases, but chemical rockets produce a mix of heavier species, reducing the exhaust velocity. Rocket engines become more efficient at high velocities, due to greater propulsive efficiency and the Oberth effect. Since they do not require an atmosphere, they are well suited for uses at very high altitudes and in space. More details
Compared to other types of jet engines, rocket engines are by far the lightest, and have the highest thrust, but are the least propellant-efficient (they have the lowest specific impulse). The ideal exhaust is hydrogen, the lightest of all gases, but chemical rockets produce a mix of heavier species, reducing the exhaust velocity. Rocket engines become more efficient at high velocities, due to greater propulsive efficiency and the Oberth effect. Since they do not require an atmosphere, they are well suited for uses at very high altitudes and in space. More details