This paper presents a robust artificial time delay based attitude regulation control of a small spacecraft under the influence of parametric uncertainties, surrounding disturbances, and time-varying actuator faults. In the artificial time delay (ATD) approach, the input-output information of the previous time instant is utilized to estimate the uncertain dynamical parts. The proposed attitude controller is designed by integrating the time delay approach with a feedback control technique. Under the proposed composite control scheme, the system states are proved to be uniformly ultimately bounded (UUB) stable using the Lyapunov analysis. Moreover, the problem of unwinding in the quaternion representation, due to which the spacecraft consumes more time and energy, is also resolved under the proposed scheme. The performance of the proposed control methodology has been validated using numerical simulations. Furthermore, two different control schemes are also compared to illustrate the efficacy of the proposed strategy.

The active magnetic bearings (AMB) play an essential role in supporting the shaft of fast rotating machines and controlling the displacements in the rotors due to the deviation in the shaft. In this paper, an adaptive integral third-order sliding mode control (AITOSMC) is proposed. The controller suppresses the deviations in the rotor and rejects the system uncertainties and unknown disturbances present in the five DOF AMB system. The application of AITOSMC alleviates the problem of high-frequency switching called chattering, which would otherwise restrict the practical application of sliding mode control (SMC). Moreover, adaptive laws are also incorporated in the proposed approach for estimating the controller gains. Further, it also prevents the problem of overestimation and avoids the use of a priori assumption about the upper bound knowledge of total disturbance. The Lyapunov and homogeneity theories are exploited for the stability proof, which guarantees the finite-time convergence of closed-loop and output signals. The numerical analysis of the proposed strategy illustrates the effective performance. Furthermore, the comparative analysis with the existing control schemes demonstrates the efficacy of the proposed controller.

The re-entry phase of the reusable launch vehicle (RLV) is a challenging optimal control problem because of its high nonlinearity and numerical sensitivity. In this paper, a recently proposed metaheuristic optimization algorithm, Sine-Cosine Algorithm(SCA) is employed to solve the re-entry trajectory problem for space shuttle vehicle. A cost function which maximizes the cross range along with satisfying certain boundary conditions is selected for the problem. Control inputs are parameterized with defined ranges for the implementation of SCA to solve the optimal control problem. The results demonstrate the optimal trajectory. The results obtained show efficiency and applicability of SCA for solving the trajectory optimal control problem.

This paper proposes the use of Legendre pseudospectral method (PSM) to obtain the optimal guidance strategy for a two-dimensional interceptor problem. An optimal control problem is formulated that addresses the conflicting objective of minimizing the energy usage, along with minimizing the time taken by missile to capture the target. The PSM-based guidance strategy is compared with other conventional guidance laws such as pure proportional navigation (PPN) guidance law and also evolutionary algorithm inspired differential evolution tuned proportional navigation (DEPN) guidance law. A scheme by which the PSM guidance strategy can be applied online is also included in this paper. The cost function value and the interception time indicates the superiority of the PSM-based guidance strategy.