Satellite attitude control and power tracking with energy/momentum wheels

A control law for an integrated power/attitude control system (IPACS) for a satellite is presented. Four or more energy/momentum wheels in an arbitrar y noncoplanar configuration and a set of three thrusters are used to implem ent the torque inputs. The energy/momentum wheels are used as attitude-cont rol actuators, as well as an energy storage mechanism, providing power to t he spacecraft. In that respect, they can replace the currently used heavy c hemical batteries. The thrusters are used to implement the torques for larg e and fast (slew) maneuvers during the attitude-initialization and target-a cquisition phases and to implement the momentum management strategies. The energy/momentum wheels are used to provide the reference-tracking torques a nd the torques for spinning up or down the wheels for storing or releasing kinetic energy. The controller published in a previous work by the authors is adopted here for the attitude-tracking function of the wheels. Power tra cking for charging and discharging the wheels is added to complete the IPAC S framework. The torques applied by the energy/momentum wheels are decompos ed into two spaces that are orthogonal to each other, with the attitude-con trol torques and power-tracking torques in each space. This control law can be easily incorporated in an IPACS system onboard a satellite. The possibi lity of the occurrence of singularities, in which no arbitrary energy profi le can be tracked, is studied for a generic wheel cluster configuration. A standard momentum management scheme is considered to null the total angular momentum of the wheels so as to minimize the gyroscopic effects and preven t the singularity from occurring. A numerical example for a satellite in a low Earth near-polar orbit is provided to test the proposed IPACS algorithm . The satellite's boresight axis is required to track a ground station, and the satellite is required to rotate about its boresight axis so that the s olar panel axis is perpendicular to the satellite-sun vector.