Reaksjonshjul

Reaksjonshjul, also known as reaction wheels, are a type of momentum wheel used to control the orientation of a spacecraft. They are a form of reaction engine that uses a spinning rotor to generate torque. When the rotor's speed is changed, an equal and opposite torque is applied to the spacecraft, causing it to rotate.

The principle behind a reaction wheel is conservation of angular momentum. In a closed system, the total angular momentum remains constant. By changing the angular momentum of the rotor, the spacecraft's angular momentum must also change to compensate. This change in the spacecraft's angular momentum results in a change in its orientation.

Reaction wheels are commonly used in satellites for attitude control. They are particularly useful for making small, precise adjustments to a spacecraft's pointing direction. Unlike thrusters, which expel mass, reaction wheels do not consume propellant, making them an efficient solution for long-duration missions. However, reaction wheels have a limit to how much momentum they can store. If a spacecraft needs to maintain a constant rotation for an extended period, the reaction wheel will eventually reach its maximum speed. At this point, it can no longer provide torque in that direction. To overcome this, spacecraft often employ a desaturation process, which typically involves using thrusters to offload the excess momentum from the reaction wheel.

Modern reaction wheels are often digitally controlled, allowing for very fine adjustments and complex maneuvers. They are a critical component for many space missions, enabling precise pointing for telescopes, communication antennas, and other instruments.