A rocket engine is a type of jet engine that uses only stored rocket propellant mass for forming its high speed propulsive jet.
A propellant or propellent is a chemical substance used in the production of energy or pressurized gas that is subsequently used to create movement of a fluid or to generate propulsion of a vehicle, projectile, or other object.
Rocket propellant is either a high oxygen containing fuel or a mixture of fuel plus oxidant, whose combustion takes place, in a definite and controlled manner with the evolution of a huge volume of gas.
A rocket is a missile, spacecraft, aircraft or other vehicle that obtains thrust from a rocket engine.
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Rocket engines are reaction engines, obtaining thrust in accordance with Newton's third law.
A reaction engine is an engine or motor which provides thrust by expelling reaction mass, in accordance with Newton's third law of motion.
Newton's laws of motion are three physical laws that, together, laid the foundation for classical mechanics.
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Most rocket engines are internal combustion engines, although non-combusting forms also exist.
An internal combustion engine is a heat engine where the combustion of a fuel occurs with an oxidizer in a combustion chamber that is an integral part of the working fluid flow circuit.
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.
A ballistic missile is a missile that follows a ballistic trajectory with the objective of delivering one or more warheads to a predetermined target.
Compared to other types of jet engines, rocket engines have the highest thrust, are by far the lightest, but are the least propellant efficient.
The ideal exhaust is hydrogen, the lightest of all gases, but chemical rockets produce a mix of heavier species, reducing the exhaust velocity.
The velocity of an object is the rate of change of its position with respect to a frame of reference, and is a function of time.
Hydrogen is a chemical element with chemical symbol H and atomic number 1.
Since they do not require an atmosphere, they are well suited for uses at very high altitude and in space.