Implementation and testing of a passive magnetic attitude control system for the 3U AstroBio CubeSat orbiting in the Van Alllen belt

AstroBio CubeSat (ABCS) is a mission funded by the Italian Space Agency (ASI) aimed at validating novel lab-on-chip technology that would enable the use of micro- and nano-satellites as autonomous orbiting laboratories for research in astrobiology. The 3U CubeSat ABCS will be deployed by Vega-C launch system in a circular orbit with altitude of 5900 km and inclination of 70 degrees which crosses the harsh radiative environment of the inner Van Allen belt. In fact, the operative life of ABCS is expected to be significantly shorter than Low Earth Orbit (LEO) CubeSats, therefore a passive magnetic attitude control system (PMACS) was designed to (i) detumble the satellite and (ii) control its attitude to maximize the exposure of the body-mounted solar panels to the solar radiation. The PMACS consists of permanent magnets, producing a control torque rotating the satellite in the direction of the geomagnetic field vector, and soft-magnetic alloy strips, or hysteresis strips, performing the detumbling and stabilization of the satellite. The characterization of the hysteresis strips is not trivial and pivotal for estimating the performance of the PMACS. In this work, the hysteresis loop and the magnetic permeability for the hysteresis strips were determined experimentally using a Helmholtz cage facility with feedback control. Once characterized, the magnetic devices were installed onto a test unit of ABCS and integrated to a spherical air-bearing facility, which allows friction-less rotation. The use of the air-bearing together with the Helmholtz cage, recreating the magnetic field that will be experienced by ABCS in orbit, allows testing the PMACS in an environment which is significantly similar to the real operative one. The PMACS was tested under several detumbling conditions and experimental data allowed a quantitative evaluation the dissipative effect due to magnetic hysteresis, contributing in determining the optimal configuration for the PMACS devices.