Dynamic Event-triggered Spacecraft Attittude Control

Cell Sat is a kind of standardized microsatellites with its character of plug-andplay and free-separation-assembly,which is capable of large-scale on-orbit construction,on-orbit service,and on-orbit maintenance.Consequently,Cell Sat has got a lot of attention since it was proposed.A typical application scenario is the attitude takeover control of large disabled spacecraft.In this scenario,dozens of Cell Sat will be attached on the surface of a disabled spacecraft to take over the attitude and orbit control system of the disabled spacecraft,then all the other available functions of the disabled spacecraft will be recovered with the help of a fullyfunctioning attitude and orbit control system(AOCS).In the scenario of spacecraft attitude takeover control,there exist two problems,one of them is(local)limited communication,the other one is input saturation.Consider that the sensor Cell Sat and the controller Cell Sat attach on the different position of a disabled spacecraft,it’s unavoidable to adopt wireless network to transmit the measured attitude information from the sensor Cell Sat to the controller Cell Sat.Therefore,there exists a serious problem of(local)limited communication.Besides,the size of a standardized Cell Sat is limited.Although the actuator consists of dozens of actuator Cell Sat,the resultant moment of all these actuator Cell Sat is still very low.Thus,there exists a serious problem of actuator saturation in spacecraft attitude take over control.At last,it’s necessary to ensure the high control precision of the AOCS to make sure that the devices on the controlled spacecraft can work normally.In this paper,a dynamic event-triggered mechanism(DETM)is proposed to cope with the problem of(local)limited communication in spacecraft attitude take over control.An adaptive neural network(NN)attitude tracking control system is designed on the basis of this DETM.Corresponding control stability analysis,Zeno behavior analysis,and numerical simulation demonstrate that the proposed control system is capable of improving the minimum inter-event time(MIET)between any contiguous triggering instants significantly without decreasing the control precision,which means the proposed control system is effective in dealing with(local)limited communication in spacecraft attitude take over control.Then a dynamic-loop gain function based control system with an extra adaptive compensate term and the ability to deal with input saturation is proposed on the second part,which is an extension of the proposed Dynamic event-triggered adaptive NN attitude control system.Both the theoretical analysis and the numerical simulation demonstrate that this control system can solve the problem of input saturation and(local)limited communication at the same time without decreasing the control precision.Finally,on the basis of the dynamic event-triggered spacecraft attitude takeover control system with input saturation proposed in the second part,an estimated dynamics system in correspondence with the spacecraft dynamics system is inserted in the controller Cell Sat and a consecutive controller is designed with the estimated states generated from the estimated model.Under the premise of high control precision,it’s possible to improve the MIET maximally with the application of this model-based control system,the possibility of limited communication can be cleared thoroughly and the actuator saturation can also be avoided.