On this slide, we show a picture of a Atlas rocket at the left and a picture of the Space Shuttle at the right. The Atlas rocket was developed in the late 1950’s and used small Vernier rockets on the sides of the missile to provide maneuvering and balance. The Space Shuttle was designed in the late 1970’s and employed the more modern gimbaling of the main engines to provide for control during launch.
There are four major components to any full scale rocket; the structural system or frame, the payload system, the guidance system, and the propulsion system. The guidance system of a rocket includes very sophisticated sensors, on-board computers, radars, and communication equipment. The guidance system has two main roles during the launch of a rocket; to provide stability for the rocket, and to control the rocket during maneuvers.
The motion of any object in flight is a combination of the translation of the center of gravity and the rotation of the object about its center of gravity. Many different methods have been developed to control rockets in flight. All of the control methods produce a torque about the rocket’s center of gravity which causes the rocket to rotate in flight. Through an understanding of the forces acting on the rocket and the resulting motion, the rocket guidance system can be programmed to intercept targets, or to fly into orbit.
Stability of a Rocket
A stable rocket is one which naturally returns to its flight configuration when it is perturbed from that configuration. For simple rockets flying within the atmosphere, stability is assured if the aerodynamic forces acting through the center of pressure are kept below the rocket center of gravity. Fins located at the bottom of the rocket, or weight added to the top of the rocket help to establish this condition. For complex rockets, or for rockets flying above the atmosphere, stability can be provided by the guidance system, using the same methods employed for maneuvers.