Principles of Design of Magnetic Devices for Attitude Control of Satellites

Satellites with directional instrumentation, such as the antenna system of the communications satellites, require attitude control to keep this instrumentation properly on target. For example, a spin imparted to the satellite at time of launch gives it a sort of gyroscopic stability. However, complete attitude control requires some available torque to correct the direction of the spin axis. In the orbiting satellite the earth's gravitational field is balanced by centrifugal force, leaving the earth's magnetic field as a convenient means for interaction torque. Suitable interaction with the earth's magnetic field can be set up by electromagnets, or by air-core coils of large area, either of which can be turned on or off at will to provide attitude correction as needed. Small permanent magnets can be designed and installed to cancel out residual magnetic moment in the satellite, which if permitted to interact with the earth's field could cause precession of the spin axis. Other miscellaneous torque applica893