What are Magnetorquer?

A magnetorquer or magnetic torque (torque rod) is used in satellites to provide attitude control and helps in stabilizing and maintaining the satellite’s orientation. Magnetorquers act as actuators for satellites and are usually built from electromagnetic coils.

Magnetorquer works on the principle of laws of electromagnetics. A current-carrying loop acquires a magnetic dipole moment and as a result, in the presence of an external magnetic field, the loop experiences a torque. Since outer space has a magnetic field due to earth, in the presence of this field the magnetorquer can exert torque on the satellite when current is passed through it. As a result, the magnetic field around the satellite interacts with the Earth’s magnetic field, thus producing torque on the satellite. In this manner, the angular momentum of the satellite can be changed and controlled. 

Magnetorquers are classified based on the realization of the coil and the number of turns of the coil. Unlike thrusters, they do not require propellant, so they could  work indefinitely as long as sufficient power is available to match the resistive load of the coils.

Magnetorquers are also used as a part of a three-axis control system when low power and little physical volume are available onboard the spacecraft. They can be stably mounted on surfaces of the satellite body and can provide three-axis stabilization if three magnetorquers are mounted orthogonal to each other. They can sometimes be used to unload the momentum of control actuators such as reaction wheels.