Magnetorquers produce a magnetic field around the satellite which interacts with the Earth's own magnetic field, thus producing a torque on the satellite. In this manner the angular momentum of the satellite can be changed and controlled.

What is magnetic torque?

A magnetic field exerts a torque which tries to align the normal vector of a loop of current with the magnetic field. The size of the torque on a loop of current is torque = (# turns) * (current) * (loop area) * (mag field) * sin(theta) where theta is the angle between the magnetic field and the loop's normal vector.

What does a Magnetorquer do?

The magnetorquer creates a magnetic dipole that interfaces with an ambient magnetic field, usually Earth's, so that the counter-forces produced provide useful torque. ...