Multi-loop robust control of dumbbell structure spacecraft attitude

Attitude maneuvers of dumbbell-shaped flexible spacecraft are bottlenecked by rigid-flexible cross-coupling and dense, extremely low-frequency structural modes. In this paper, consider the case of large flexible spacecraft with low flexural modes and coupling with the bandwidth of the control system. To circumvent the frequency aliasing and dimensionality explosion inherent in complex online adaptive estimators, this paper proposes a passivity-based, dual-loop robust control framework. At the trajectory level, a sinusoidal spectral-notch path planning algorithm is formulated to analytically enforce source energy isolation precisely at the structural fundamental frequency. At the execution level, an outer-loop robust PD controller accommodates lumped uncertainties, while an inner-loop, collocated Positive Position Feedback (PPF) controller redistributes robustness through a wide-notch damping envelope ( ξ ci ∈ [ 0.5 , 1 ] ) to tolerate extreme parameter mismatches. Simulation results demonstrate that the proposed strategy improves steady-state pointing accuracy by two orders of magnitude (from 2 × 10 − 4 ∘ / s to 8 × 10 − 6 ∘ / s ) and suppresses flexible disturbance torque by 88.3%. Furthermore, the attitude stabilization time is reduced by 36% (23.7 s), and global asymptotic stability is strictly maintained even under severe, synchronous perturbations (e.g., ± 20 % inertia and ± 15 % resonance frequency shifts).