Three-axis Attitude Control using only Magnetorquers for a Sun-Pointing Microsatellite

The interest in adopting magnetic actuators for attitude control, increases as the interest in microsatellites arises. In fact, the magnetic control is a valid choice for missions in which satellites have a low weight and have no sub-degree requirement for pointing accuracy. In this work we analyze the scenario of the future UniSat5 mission that will be a microsatellite in a quasi-polar Low Earth Orbit. The primary purpose of this work is to extend the application of a three-axis magnetic control to a Sun-pointing mission. Three dierent phases are investigated: detumbling, Sun-pointing maneuver and pointing control. For the detumbling phase, the classic Bdot law and the modied Bdot law are used to dissipate the residual kinetic energy after the launcher release. Afterwards, to achieve the pointing to the Sun, a bang-o maneuver is applied. In this phase the solar panels are stowed and, according to the mass distribution, the satellite is considered with a spherical inertia. When attitude angle errors are in the range of 20 deg, the pointing control is activated. The pointing control algorithm is based on the average linearized dynamics in an orbit, assuming that the dynamics is almost periodic. The control gain matrix is found using the LQR approach. By introducing the gravity gradient there are constant torque components which lead to chose a PID controller. The stability of the controlled system is studied in the Floquet theory.