Thruster is one of the most common and widely used actuators for spacecraft attitude control. Unlike the other actuators such as reaction wheels or control momentum gyroscopes(CMG), thruster has some inherent restrictions. First of all, it has limitation of fuel consumption. Generally, thruster is propellent-based system. To make torque for attitude control, the thruster should emit some chemical substances which are stored in propellent tank. Spacecraft can rotate or move to desired direction through the propulsion. However, because of weight and volume restriction of spacecraft, the tank capability cannot be increased much bigger. In space, absolutely, it is impossible to refuel or replace the tank as well. Consequently, fuel saving becomes an important issue for the spacecraft attitude control. At this perspective, optimization control can be a good alternative manner instead of the conventional. It can provide good performance with less fuel for the mission purpose. The resulting response absolutely depends on the objective function. Moreover, optimization control is very intuitive and convenient for engineers to impose their design purpose into the system performance. For instance, if it has more weight on the control input in the cost function, the spacecraft's performance becomes fuel-efficiency. Agile spacecraft attitude control can be fulfilled as well if the objective function is modified for the purpose.
There exist many different kinds of constraints in the design of spacecraft attitude control. Unfortunately, however, all of controllers cannot cope with them directly. Most of them are ignored or sometimes additional functions are required. In this paper, therefore, constrained optimization control which is able to take account of the constraints is introduced briefly. The comparison of various controllers' performance are shown in simulation works. The constrained optimization is also verified through some examples.