Reaktiopyöriä

Reaktiopyöriä, also known as reaction wheels, are a type of flywheel used for attitude control of spacecraft and satellites. They are a form of angular momentum control device that operates by conserving angular momentum. A reaction wheel consists of a motor connected to a flywheel. When the motor spins the flywheel, a torque is exerted on the spacecraft in the opposite direction. This torque can be used to change the orientation of the spacecraft.

The principle behind reaction wheels is Newton's third law of motion, which states that for every action, there is an equal and opposite reaction. By accelerating or decelerating the flywheel, a controlled torque is generated, allowing the spacecraft to rotate around its axes. This is a reaction to the internal change in angular momentum within the spacecraft.

Reaction wheels are particularly useful for making small, precise adjustments to a spacecraft's attitude over long periods. They are also highly energy-efficient compared to other attitude control systems like thrusters. However, reaction wheels have a limitation known as saturation. If a spacecraft needs to maintain a continuous rotation for an extended time, the flywheel can spin up to its maximum speed. At this point, the reaction wheel cannot provide any further torque, and the spacecraft's attitude can no longer be controlled by that wheel alone. To overcome saturation, spacecraft often employ other methods, such as using thrusters to desaturate the wheels, which involves spinning them down to their nominal speeds.