Abstract
CubeSats are being increasingly specified for demanding Earth observation and astronomical applications where precise pointing, agility, and stability are critical requirements. Such precision is difficult to achieve in the case of CubeSats, mainly because of their small moment of inertia, means that even small disturbance torques, such as those due to a residual magnetic moment, have a significant effect on the attitude of spacecraft. In addition, hardware limitations make the task more challenging. The effect of magnetic disturbances has shown itself by the problem of high tumbling rates observed on several CubeSat missions, post-flight analyses indicate that this is often due to un-modelled magnetic moments, mainly caused by the current flowing in the spacecraft, and the fact that CubeSats are often not designed with magnetic cleanliness in mind. However, by contrast, the other typical attitude disturbance sources for spacecraft (gravity gradient, aerodynamic, and solar radiation pressure torques) decrease significantly when the satellites become small. We investigated in this research the source of the residual magnetic field in CubeSats and the effect of the resulting disturbance on the attitude of the spacecraft. It has been found that, although the disturbances may be minimised by good engineering practice, in terms of reducing the use of permeable materials and minimising current-loop areas, these disturbances can still be an issue when a high degree of stability is required. We, therefore, proposed a new technique using a network of magnetometers to characterise and then compensate the residual magnetic moment on the ground and in flight. A hardware prototype has been developed and successfully tested with the engineering model of the boom payload of Alsat-1N CubeSat, magnetic air coils, and permanent magnets in a Helmholtz coils arrangement by implementing a network of eight miniature 3-axis magnetometers. These are used to determine the strength, the centre, and the direction of the dipole of the magnetic source.