Study On Dynamics And Control Of Electromagnetic Docking For Microsatellites

With the development of space telescopes and other large spacecraft, the on-orbit reconfiguration and on-orbit assembly of on-orbit servicing in aerospace field have caused more and more attention of researchers. With standardization, modularization, short development cycle consisting and easy to constitute constellations, Cube Sat have important research value both in on-orbit reconfiguration and on-orbit assembly. The technology of rendezvous and docking has a central role in the on-orbit reconfiguration and on-orbit assembly. Propellants employed in the traditional rendezvous and docking cause fuel consumption, optics pollution, plume impact, heat emissions and other issues. While electromagnetic rendezvous and docking, a new rendezvous and docking technology, has advantages of no fuel consumption, no docking impact, effectively avoiding pollution of optical elements caused by plume. Combining Cube Sat and the technology of electromagnetic docking, this article will research the space electromagnetic docking problem of Cube Sat. The main contents include the following aspects:Firstly, this paper establishes the“CM” orbit coordinate system and “CM” calculation coordinate system with the centroid “CM” of two spacecraft systems as the origin of coordinates. For the complexity of the electromagnetic force and electromagnetic torque models generated by the energized solenoids without research foundation yet, the electromagnetic docking device is simplified. This paper establishes the magnetic dipole far-field model of single coil. Afterwards, the electromagnetic force and electromagnetic torque models during space electromagnetic docking are established. On the basis of verifying the reliability of electromagnetic simulation software Ansoft Maxwell, this paper makes data correction from the solenoid model with core to the single coil model.Secondly, the influences of disturbance force and disturbance torque caused by geomagnetic field and other disturbances are analyzed in the process of docking, and on this basis, the space electromagnetic docking dynamics model is established. First, the problem of one-dimensional orbit without attitude during space electromagnetic docking is considered, and one-dimensional flexible docking trajectory is designed. With respect to one-dimensional electromagnetic docking problem, the sliding mode controller based on reaching law is proposed according to the reference trajectory. For the chattering problem in the sliding mode control process, the quasi-sliding mode control approach is adopted.Then, the control problem of one-dimensional orbit and attitude of small angle is considered. With respect to one-dimensional electromagnetic docking problem of small angle, considering the case of different current in the energized solenoid of spacecraft, this paper derives and simplifies the one-dimensional electromagnetic force and electromagnetic torque of small angle in the process of space electromagnetic docking, and comparisons with the far-field model are made to analyze error characteristics, and the one-dimensional electromagnetic force and electromagnetic torque models of small angle are established. In the process of one-dimensional orbit control and attitude control of small angle, the flexible docking trajectory of attitude control is designed. The sliding mode control method is adopted to achieve one-dimensional electromagnetic docking of small angle and that the system state will reach the sliding surface in a finite time and the stable state finally is proved. The simulation results show that the sliding mode control method can achieve the flexible docking for one-dimensional orbit and attitude of small angle, and the tracking performance regarding reference trajectory is good.Finally, considering the two-dimensional electromagnetic docking problem in the case of same current in the energized solenoid of spacecraft, assuming that the electromagnetic docking satisfies self-docking condition. The electromagnetic force expressions of two-dimensional electromagnetic docking case of small angle are derived and compared with the far-field model to analyze error characteristics, and the two-dimensional electromagnetic force and electromagnetic torque models of small angle are established. And on this basis, the two-dimensional electromagnetic docking dynamics equations of small angle are established, and feedback linearization is conducted. With respect to the control problem of two-dimensional electromagnetic docking, the reference trajectory designed before is used, and the robust mixed H₂/H_∞ controller under poles assignment constraint is designed. With rational poles allocation, the system can reach steady state quickly, thus achieve the purpose of two-dimensional electromagnetic docking of small angle. The simulation results show that the robust mixed H₂/H_∞ control method can achieve the two-dimensional flexible docking of small angle, and the tracking performance regarding reference trajectory is good.