The attitude control subsystem plays a significant role in the overall performance of the spacecraft. Attitude control subsystem is vitally important to design the control system with rapid response performance, high control precision and insensitive to external perturbations. In this paper a novel fault-tolerant control design technique against faulty thrusters is investigated. This technique uses adaptive sliding mode control with application to spacecraft attitude maneuvering control system. The principle of the proposed fault-tolerant control scheme is to design sliding mode attitude controller using the time variable sliding surface to compensate the effect of partial loss of the actuators effectiveness. This adaptive law calculates the ability of spacecraft maneuvering in following the control input based on kinematic energy of the estimated and real model of the spacecraft. It is shown that the presented controller can accommodate the actuator faults, even while resisting the external disturbances. Moreover, in the control law scheme the effect of actuator saturation/constraint has been considered. An additional advantage of the proposed fault-tolerant control strategy is that the control design does not require a fault detection and isolation mechanism to detect, separate, and identify the actuator faults on-line. The associated stability proof is constructive and accomplished by the development of Lyapunov function candidate, which shows that the attitude orientation and angular velocity will globally asymptotically converge to zero. Moreover, several numerical examples are presented to demonstrate the efficacy of the proposed controller despite the external perturbations, moment of inertia uncertainty and faulty actuators. The numerical results clearly demonstrate the good performance of the adaptive sliding mode control despite the actuator fault comparison with some other controllers.
Virtual simulation is one of the best methods for training students and understanding events and has been used in many fields of science yet, for example: space researches. For this reason, creating of an environment that can simulate the operations of satellites will be very usable and appropriate. This paper will present the details of a newly constructed 6-DoF experimental Satellite Virtual Simulator (SVS) facility at the Space Research Laboratory (SRL) at the K.N.Toosi University of Technology. SVS is used for studying the translational and rotational motions of a satellite and testing the control and communication concepts. The main components of the facility are 3-D screens, video projectors, user interface, central server system, 3-D glasses for users and its modeling software.
By considering transition-metal (Shiba-Rusinov model) and rare-earth metal impurities (Abrikosov-Gorkov theory) effect on a many-body system, i.e., a BCS s-wave superconductor, quantum bipartite entanglement of two electrons of the Cooper pairs in terms of the exchange interaction, J, the potential scattering, V(playing an important role, unexpectedly), and the distance of two electron spins of the Cooper pair is calculated at zero temperature by using two-electron spin-space density matrix (Werner state). In transition-metal case, we find new quantum phase transitions (QPTs). The changes of J, which causes to have localized excited state, V and the pairing interaction (via energy gap) lead to the displacement of the QPTs (interactions act in the same direction, however sometimes the pairing interaction causes the competition with other interactions), regardless of their effects on the value of concurrence. Determining the allowable values of all interactions by itself is not possible, due to the smallness of the perturbed Green’s functions (appearing in the density matrix). For non-magnetic and magnetic (rare-earth) impurity cases, concurrence versus the distance and collision times is discussed for all finite and infinite Debye frequency. The quantum correlation, instability of the system and what's more important QPT can be tuned by the impurity.
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