Attitude control — III

THE AGE OF SATELLITES is here. With it has come some interesting attitude control problems. For many uses, it is desirable to have a satellite oriented in a unique attitude with respect to the earth. If such a unique stable attitude exists, the attitude-control problem is reduced to a damping problem. Two methods have been proposed to obtain a stable attitude. These methods use (1) the gradient in the earth´s gravitational field, and (2) aerodynamic torques. Each method requires that the vehicle have certain properties. In gravity gradient stabilization, it is necessary that the vehicle have a single axis about which the moment of inertia is a minimum. In the stabilized position, this axis becomes aligned to the vertical.^1–4 In aerodynamic stabilization, it is necessary that the center of pressure lie behind the center of mass in the direction of the vehicle´s velocity.