In the aerospace context, ACS stands for "Attitude Control System." This system is responsible for controlling the orientation or attitude of a spacecraft or aircraft.
It typically consists of sensors, actuators, and control algorithms that work together to maintain the desired orientation of the vehicle relative to a reference frame. The ACS can use a variety of methods to control the attitude of the vehicle, such as thrusters, reaction wheels, or gimbal-mounted propulsion systems. The ACS is an essential component of a spacecraft or aircraft, as it is responsible for maintaining stability and control during flight.