We know that rockets launch satellites. The rockets are fired from the ground into the outer space. Once the rocket reaches extremely thin air up, the rocket's navigational system releases the satellite. Rockets are fired once again to ensure some separation between the launch vehicle and the satellite itself. A rocket is controlled very precisely to insert a satellite into the desired orbit. Reaching the outer space it starts to revolve around a planet or smaller celestial body. A satellite could be designed to either orbit the earth, the moon or any other planet.
In order to go to the outer space, rockets have to escape the earth’s gravity. The speed that is necessary to break away from the gravitational pull of a planet or moon is called the escape velocity. In other words, escape velocity is the minimum velocity an object must have in order to escape the gravitational field of the earth so that it does not fall back to earth. Each planet has a different escape velocity.
Achieving escape velocity is one of the biggest challenges in the aerospace world. In the olden times, an enormous amount of fuel was required for achieving this task. More fuel demanded more space. Heavier became the object carrying the fuel and so more thrust was needed to lift it. This again demanded fuel. With the invention of more efficient fuel and new methods of propulsion, lighter vehicles are designed to achieve escape velocity.