Rocket and space technology is based on the application of orbital mechanics or flight mechanics. Orbital mechanics deals with the motions of artificial satellites and space vehicles under the influence of gravity, atmospheric drag, and thrust. Orbital mechanics is a modern branch of celestial mechanics which is the study of the motions of natural celestial bodies such as the star, galaxies, moon and planets. Isaac Newton (1642-1727), a 17th century mathematician who put forward the laws of motion and formulated the law of universal gravitation is the theoretical founding principle of orbital mechanics. The engineering applications of orbital mechanics include ascent trajectories, reentry and landing, numerical modeling and simulations, lunar, interplanetary trajectories, communication satellites, space stations,space shuttles and inter-planetary communication.