Reaction wheel

A reaction wheel is like a toy top. When you spin a top, it stays upright and doesn't fall over. A reaction wheel is a machine that works the same way, but it's much bigger and much faster. Instead of spinning on the floor like a top, a reaction wheel spins inside a spacecraft or satellite.

When a spacecraft needs to change direction, it uses the reaction wheel. If you try to turn a car while it's not moving, it's hard to turn. But if you're driving, it's easier to turn. That's because the car has something called momentum. When the spacecraft moves, it has momentum too. When the spacecraft needs to change direction, the reaction wheel will spin faster or slower, depending on the direction it needs to go. This makes the spacecraft change its direction, just like the toy top stays upright even though you turn it.

It's important to note that reaction wheels don't work forever. They eventually slow down and need to be reset. Satellites can use other methods to maintain their position, including small rockets, but reaction wheels are popular because they are low-impact -- they require less fuel and are less likely to damage the satellite.