Electromagnetic Attitude Control System Providing Small Residual Accelerations on Board the Spacecraft

We investigate the electromagnetic attitude control system of the spacecraft Foton that uses three current-carrying coils as its actuators. Each coil has a few turns lying along a great circle of the sphere that is outer shell of the landing capsule. The coils are in three mutually perpendicular planes. The center of the sphere is the point of intersection of the planes. One of the lines of intersection coincides with the spacecraft longitudinal axis. Electric currents in the coils produce the magnetic moment, which interacts with the Earth magnetic field and makes a torque acting upon the spacecraft. The spacecraft attitude control is implemented by change of the currents in the coils. We investigate two control laws that reduce the spacecraft angular rate and stabilize the spacecraft gravity gradient orientation. Measurements of a triaxial magnetometer need only to form these laws. Realization of the laws requires a few watts of electric power. We test the laws by the mathematical modeling and show that their use in the spacecraft Foton provides decrease of residual accelerations on its board up to ten times.