Validation of the Attitude Determination and Control System of a Deorbit Device Equipped with an Electrodynamic Tether Using Hardware in the Loop Testing

The functionality of the attitude determination and control system (ADCS) of an autonomous deorbit device based on electrodynamic tether technology was validated in ground and under space representative conditions by using Hardware-in-the-loop (HIL) testing. A nano attitude dynamics experimental setup with an air bearing table, mass balancing mechanism, Sun emulator, and attitude heading and reference system (AHRS), was designed and fabricated. It provides three degrees of freedom and emulates orbital conditions for HIL experiments. The work evaluated the ADCS performance through two stages of HIL testing. In the first stage, an internal Extended Kalman Filter (EKF) was assessed for attitude determination by feeding the AHRS measurements under dynamic conditions. The results show that the EKF accurately tracks the reference attitude of the AHRS with a maximum error of 0.42º. In the second stage, the EKF was fed with the measurements of the ADCS system of the deorbit device, which include a magnetometer, sun sensors and a gyroscope. The maximum attitude error was 0.82º during eclipse and improved to 0.38º in sunlit conditions. In addition, the potential interference sources impacting on the ADCS system were characterized by using a dedicated experimental setup based on the measurements of a network of magnetometers. The residual magnetic dipole and the magnetic field generated by the actuation of the cold-gas valve and the motors of the tether deployment mechanism were measured. The maximum residual dipole moment of the deorbit device was 0.0214 Am^2, whereas the dipole of the valve was ≃ 0.0109 Am^2. The motor actuation is the dominant source because, as shown by the experiments, it can produce errors on the magnetic field direction exceeding 10º. As consequence, it was decided not to use the measurement of the magnetometer during the tether deployment phase.