Magnetorquer

A magnetorquer is an attitude control actuator consisting of a wire coil — often wound around a ferromagnetic core, or etched into a circuit board on small satellites — that creates a magnetic dipole when energised. That dipole interacts with Earth's magnetic field to produce torque on the spacecraft, exactly as a compass needle feels a twist. The virtues are robustness itself: no propellant, no moving parts, no plume, indefinite operation on modest electrical power. The physics imposes the limit: torque can only be generated perpendicular to the local field line, so full three-axis authority is impossible at any instant — control schemes exploit the field's changing direction around each orbit to reach all axes over time. In practice magnetorquers fill two roles: on larger satellites they quietly unload the momentum that accumulates in reaction wheels, replacing thruster firings and saving propellant; on CubeSats and small satellites they often *are* the attitude system, providing detumbling after deployment and coarse pointing at a few degrees. Beyond roughly 1,000 km their leverage fades with the field strength, making them a distinctly low-orbit technology.