Magnetic Cleanliness Program on CubeSats and Nanosatellites for Improved Attitude Stability

CubeSats are being increasingly specified and utilized for demanding astronomical and Earth observation missions where precise pointing and stability are critical requirements. Such precision is difficult to achieve in the case of CubeSats, mainly because of their small moment of inertia, this means that even small disturbance torques, such as those due to a residual magnetic moment are an issue and have a significant effect on the attitude of nanosatellites, when a high degree of stability is required. Also, hardware limitations in terms of power, weight and size, make the task more challenging. Recently, a PhD research program has been undertaken at the University of Surrey, to investigate the magnetic characteristics of CubeSats, it has been found that the disturbances may be mitigated by good engineering practice, in terms of reducing the use of permeable materials and minimizing current-loop area. This paper discusses the dominant source nanosatellites disturbances and presents a survey and a short description of magnetic cleanliness techniques to minimize the effect of the residual magnetic field. It is mainly intended to supply a guide for CubeSat community to design future CubeSats with improved attitude stability. We present then our findings to date of a new technique of the residual magnetic dipole determination for CubeSats and Nanosatellites. This method is performed by implementing a network of eight miniature 3-axis magnetometers on the spacecraft. These are used to determine the strength, the direction and the center of the magnetic dipole of the spacecraft dynamically in-orbit and in real-time. This technique will contribute to reduce the effect of magnetic disturbances and improve the stability of CubeSats. A software model and a hardware prototype using eight magnetometers controlled via a Raspberry-Pi were developed and successfully tested with the boom payload of the Alsat-1N CubeSat and a magnetic air coil developed for validation purposes.