Rocket Engine : A rocket engine is like a jet engine generates thrust by the jet of exhaust gases is going out at high velocity at the rear.
A rocket differs from a jet engine as the former carries all its supplies of oxygen in addition to the fuel with it, whereas the latter is dependent upon a continuous feed upon of atmospheric oxygen.
There are two types of fuels are used in the rocket, the solid fuel and the liquid fuel. In the solid fuel rocket the oxygen is carried in the form of chemicals which are mixed with the fuel. But in the liquid fuel rocket, the oxygen is carried in separate fuel tanks. Thus a rocket does not depend upon the oxygen in the atmosphere for its working Hence a rocket can function in vacuum and its test is independent of the environments.