Composite back stepping anti-unwinding control of spacecraft with finite time convergence

Quaternion representation of spacecraft results in dual equilibrium points. Unwinding phenomenon occurs if both the points are not considered stable while designing control law. This research note proposes anti-unwinding attitude stabilization control of rigid body spacecraft in presence of external disturbance and inertial uncertainties. In pursuit of our goal, we formulated sliding surface using scalar component of quaternion and developed composite anti-unwinding control law using back-stepping technique (BT), in accomplice with sliding mode control (SMC). Furthermore, state transformation is performed to facilitate application of observer for estimation of lumped uncertainties. We employed extended state observer (ESO) to compensate for external disturbance and inertial uncertainties. The control law gives precise and smooth steady state performance along with faster transient response. Additionally, it has better uncertainty rejection capabilities and alleviates chattering phenomenon. Close loop stability of the system is proved using Lyapunov's theory and Barbalat's lemma in finite time (FT). Simulation results demonstrate effectiveness of the presented control law.