Guaranteed Safe Spacecraft Docking with Control Barrier Functions

TL;DR

This paper develops a control strategy using Robust Control Barrier Functions to ensure safe spacecraft docking despite disturbances, guaranteeing finite-time docking within a safe set, validated through simulations.

Contribution

It introduces a novel control approach that guarantees safe docking under disturbances by incorporating worst-case disturbance considerations into the control barrier framework.

Findings

Guarantees safe docking within a set despite disturbances

Validated approach through simulations of asteroid landing and spacecraft docking

Ensures finite-time docking while maintaining safety constraints

Abstract

This paper presents a strategy for control of a spacecraft docking with a non-maneuvering target in the presence of safety constraints and bounded disturbances. The presence of disturbances prevents convergence to a unique docking state, so in our formulation, docking is defined as occurring within a set constructed using prescribed tolerances. Safety is ensured via application of Robust Control Barrier Functions to render a designated safe set forward invariant for any allowable disturbance. However, this safety strategy necessarily presumes a worst-case disturbance, and thus restricts trajectories to a subset of the safe set when a worst-case disturbance is not present. The presented controller accounts for this restriction, and guarantees that the spacecraft both remains safe and achieves docking in finite time for any allowable disturbance. The controller is then validated in simulation for a spacecraft landing on an asteroid, and two spacecraft docking in low Earth orbit.