A satellite has to keep pointing the right way. A sensor measures its attitude, a computer picks a thruster, and a tiny jet turns it round — without pushing it off course.
Attitude control means keeping a spacecraft pointed the right way. A satellite must aim its antennas at the ground and its solar panels at the Sun, and it must do so while slowly drifting and turning. Small thrusters around the body give it the tiny pushes needed to correct its pointing, without sending it off its orbit.
Attitude control is a closed loop: measure, decide, push, measure again. Opening the spacecraft shows the whole loop — the sensor that watches the stars, the computer that decides, and the thrusters that do the nudging — working together.
The attitude sensor works out which way the spacecraft is currently facing, often by taking pictures of the stars and matching them to a map. This measurement is the starting point for every correction.
The control computer compares the measured pointing with the target. If they differ, it works out which thrusters to fire and for how long, and turns that into commands for the valves.
Opening the right valve lets propellant flow from the tank, along the feed lines, to the chosen thruster. Only a very short pulse is needed for a small correction.
The thruster burns or expels its little charge of propellant and throws it out as a jet. By reaction the spacecraft feels a small push, just as a rocket does, but far gentler.
To turn without drifting, the computer fires two matched thrusters on opposite sides in the same direction. Their pushes cancel out so the spacecraft's centre stays put, yet the pair together rotates it. The loop then repeats, measuring again until the pointing is right.
Attitude is which way the spacecraft is pointing. Attitude control keeps a satellite aimed correctly so its antennas face the ground and its solar panels face the Sun.
Fire a thruster off to one side and its push turns the spacecraft as well as moving it. Placing thrusters around the edges lets the computer make turning forces on purpose, and cancel out unwanted ones.
By firing two matched thrusters on opposite sides in the same direction. Their pushes cancel out so the centre of the spacecraft stays put, but the pair together still rotates it.
Each pulse gives a small, repeatable kick. Many short pulses let the computer steer very precisely and stop the moment the pointing is right, instead of overshooting with one long burn.
Its job is only to change the pointing, not the orbit. Any small drift it does cause is corrected separately, and the amount of propellant used is tiny.