Magnetorquers and reaction wheels?

[vanihba]

What is the physics behind magnetorquers and reaction wheels which help in satellite attitude determination and control?

 

[Drakkith]

When you accelerate a reaction wheel, the satellite moves in the opposite direction. (Newtons third law) Using a couple of these you can turn the satellite in any direction.

For the magnetorquer, I can give the explanation from the wikipedia article: en.wikipedia.org/wiki/Magnetorquer

In satellite systems, a magnetorquer or magnetic torquer is a system for attitude control, detumbling and stabilization built from electromagnetic coils. The magnetorquer develops a magnetic field which interfaces with an ambient magnetic field, usually the Earth's, so that the counter-forces produced provide useful torque.