The algorithm to control the in-plane relative motion of a spacecraft for contactless space debris removal

1Khoroshylov, SV
1Institute of Technical Mechanics of the National Academy of Science of Ukraine and the State Space Agency of Ukraine, Dnipropetrovsk, Ukraine
Space Sci. & Technol. 2019, 25 ;(1):14-26
Publication Language: Russian
The article is devoted to the improvement of the technology for contactless space debris removal called "Ion Beam Shepherd". The control law has been synthesized to maintain the required position of the shepherd spacecraft relative to the space debris object in the orbital plane by changing the thrust of only one compensating ion thruster in a certain small range compared to its nominal value. The synthesis is carried out using the method of mixed sensitivity. The method provides the necessary trade-off between robust stability, performance, and control costs.  This takes into account the impact of the ion beam, external disturbances, inaccurate determination of the relative position, as well as non-ideal reactive actuator. The requirements for the synthesized controller are set in the frequency domain using the selected weight functions.
         The results of the synthesis are verified using a formal criterion based on the concept of structured singular values and by computer simulation using a non-linear mathematical model.  The latter takes into account a wide range of orbital perturbations acting on the system. The control law ensures that the shepherd spacecraft moves at a certain small distance in front of a debris object while the ion beam effectively transfers the de-orbiting impulse to it. A significant advantage of the proposed control from the point of view of the propellant consumption is shown in comparison with the traditional approach based on the use of hydrazine thrusters. This advantage is one of the key factors for the choice of control due to the significant duration of the phase of space debris removal.
Keywords: compensating thruster, control law, ion beam shepherd, propellant consumption, robustness, space debris