Satellite attitude control and power tracking with momentum wheels

A control law for an Integrated Power/Attitude Control System (IPACS) for a satellite is presented in this paper. Four or more momentum wheels in an arbitrary non-coplanar configuration, and a set of three thrusters are used to implement the torque inputs. The momentum wheels are used as attitude control actuators, as well as an energy storage mechanism, providing power to the spacecraft. In that respect, they can be used to replace the currently used heavy chemical batteries, The thrusters are used to implement large torques for large and fast (slew) maneuvers and provide for the momentum management strategies. The momentum wheels are used to provide the reference-tracking torques and the torques for speeding up or slowing down the wheels for storing and releasing kinetic energy. The attitude tracking controller published in a previous work is adopted here. Power tracking for charging and discharging the momentum wheels is added to complete the IPACS framework, The torques applied by the momentum wheels are decomposed into two spaces which are orthogonal to each other, with the attitude control torques and power tracking torques in each space. This control law can be easily incorporated in an IPACS system on-board a satellite. The possibility of occurrence of singularities, where no arbitrary energy profile can be tracked, is studied for the wheel cluster considered in the paper A generic momentum management scheme is considered to null the total angular momentum of the wheels so as to minimize the gyroscopic effects and prevent the singularity from occurring. A numerical example for a low earth near polar orbital satellite is provided to test the proposed IPACS algorithm, The satellite's boresight axis is required to track a ground station. In addition, the satellite is required to rotate about its boresight axis so that the solar panel axis is perpendicular to the satellite-sun vector.