Design and Implementation of Attitude Control for 3-axes Magnetic Coil Stabilization of a Spacecraft

Abstract

Spacecrafts, especially satellites, play an ever greater rolein our daily lives as we increasingly depend on the services they provide,which in turn, more often than not, critically depend on maintainingcorrect payload attitude. As smaller educational satellites pavethe way for organization, group and privately owned pico-satellites, weexplore the possibilities of attitude control through magnetic coil actuation.We approach the whole problem, from control theory developmentto first prototype actualization and control algorithm implementation,presenting the steps taken in a user-friendly manner while pointing outthe pitfalls and drawbacks of different solutions. The control is based ona dissipative detumbling controller which after the initial phase is overriddenby the reference controller attaining final desired payload attitude.We find that a simple 8-bit, 16Mhz microcontroller unit has the su-cient processing power to continuously compute the geomagnetic fieldusing the complex International Geomagnetic Reference Field model,while simultaneously maintaining correct coil actuation. The powerconsumed by the controllers during the <300 minute control phase,from initial tumbling to desired attitude, given a typical tumbling velocityof absolute magnitude 0.2[rad/sec], is found to be no more than 150Joules across the randomly selected test scenarios. Thus we are able toconclude that three perpendicular magnetic coils, together with constantlypresent disturbances and complex geomagnetic field model preventingit from remaining at an ill-aligned attitude where one actuatingdegree of freedom is lost, provide sufficient actuation for reference controlof a spacecraft.