Magnetic-torquers-only attitude control with estimation and compensation of the residual magnetic moment

Abstract

The estimation of the Residual Magnetic Moment in a CubeSat controlled only by Magnetic Torque Bars is critical to achieving accurate attitude pointing. This process can be divided into two phases: an initial ground-based estimation using a testbed to characterize the magnetic moment prior to launch and a subsequent in-orbit estimation. This work proposes a low-cost, fully autonomous in-orbit estimation and compensation approach, incorporating several improvements over recently published methods. Moreover, we present results obtained using a magnetic-only feedback control scheme, which poses additional challenges to the robustness of the combined controller+estimator+compensator system. The analysis also includes scenarios with intermittent attitude information caused by typical eclipse periods in Low Earth Orbits. In addition, a nadir-pointing mode is evaluated under near-inertial pointing conditions to assess the behaviour of the estimator. Finally, the observability of the residual magnetic moment estimator is verified using an appropriate time-varying formulation of the innovation process.