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Anti-unwinding Attitude Control of Spacecraft using Back-Stepping Technique with Finite Time Convergence

Quaternion representation of spacecraft has double equilibrium points associated with it, which may cause unwinding phenomenon in attitude control if both equilibria are not treated as stable during control law design procedure. This paper presents anti-unwinding attitude tracking control of rigid body spacecraft in presence of external disturbance and model uncertainties. In pursuit of our goal, anti-unwinding attitude tracking control law using back-stepping technique (BT) is developed, in accomplice with sliding mode control (SMC). Sliding surface using initial value of scalar component of quaternion is formulated. Furthermore, system dynamics are transformed to facilitate application of observer for estimation of lumped uncertainties. Extended state observer (ESO) is employed to compensate for total system uncertainties. The proposed controller gives faster transient response. Furthermore, controller output is chattering free and smooth. In addition, proposed control law has superior disturbance rejection capabilities and is robust against model uncertainties. Stability analysis of closed loop system is performed using Lyapunovs theory and Barbalats lemma in finite time (FT). Numerical simulations are performed to show the efficiency of proposed control scheme.