Robust Glideslope Guidance With Inner Loop Augmentation and Non-Uniform Maneuver Pulses for Propellant Optimization

This work presents a robust and fuel-efficient glideslope guidance framework for autonomous rendezvous and docking (RVD) operations. Conventional glideslope guidance executes maneuver burns at uniform time intervals, determined solely by the overall transfer duration and number of burns. Traditional approach also lacks robustness: errors incurred during maneuver execution propagate and are only corrected in subsequent burn, leading to potential trajectory deviations. Moreover, traditional formulations do not explicitly account for fuel optimization. To overcome these limitations, we introduce two key augmentations: (i) a inner-loop controller for real-time trajectory tracking, and (ii) Non-uniform maneuver burn time obtained via offline trajectory optimization to minimize total propellant consumption under state constraints. To enable low-complexity onboard implementation, the ground-optimized burn times are learned through regression-based function approximation. Simulation results demonstrate that the proposed enhancements significantly improve both robustness and fuel efficiency compared to uniform, open-loop glideslope guidance schemes.