Attitude control is how a satellite points: sensing which way it faces with star trackers, Sun sensors and gyroscopes, then commanding torques from reaction wheels, magnetorquers or thrusters. Every mission depends on it — antennas at Earth, solar panels at the Sun, telescopes at targets.
Understanding Attitude Control
The pointing budget
Engineers decompose performance into knowledge (how well orientation is measured), control (how tightly the commanded attitude is held) and stability (how much it jitters over an exposure). Each layer has its own error tree — sensor noise, misalignments, thermal flexing between the star tracker and the payload, wheel micro-vibrations — and the system is designed against the toughest requirement, usually the payload's. The star-tracker-plus-wheels architecture that dominates today delivers hundredths-of-a-degree routinely.
Momentum management
Wheels absorb disturbance torques by spinning faster — but only up to a speed limit. Persistent one-sided disturbances (aerodynamic torque on a LEO satellite, solar pressure on a big array) pump momentum in until wheels saturate, so the ADCS periodically "dumps" it: magnetorquers torque against Earth's field, or thrusters fire in couples, letting the wheels spin back down. Momentum accounting — how much builds per orbit, how it is unloaded — quietly shapes satellite design and propellant budgets.