Extended state observer-based safe hovering control for spacecraft around asteroids

Abstract

A hierarchical safe-hovering architecture combining a linear extended state observer (ESO) and a high-order control barrier function (HOCBF) safety filter is developed for spacecraft proximity operations around irregular asteroids. In an asteroid-fixed frame, gravity-model mismatch, nonspherical gravity, environmental perturbations, and actuator errors are lumped into a total disturbance. A bandwidth-parameterized ESO estimates velocity and disturbance online for a disturbancecompensated nominal controller. Relative-degree-two HOCBF constraints enforce minimum surface clearance and maximum mission radius, while componentwise thrust limits are imposed through a real-time quadratic program (QP). Bennu-scale simulations include a 12.1% gravitational-parameter mismatch, periodic and impulsive disturbances, measurement noise, and actuator degradation. The method maintains a 0.582 m minimum safety margin with no violation, reduces steady-stage position RMSE by $\mathbf{1 1. 9 {\unicode{0x0025}}}$ relative to conventional PD control, and lowers final position error from 2.790 to 2.253 m. The QP has only three decision variables, although execution time on representative space-grade hardware remains to be measured.