Control barrier functions improve safety for robotic spacecraft capture
Control Barrier Functions for Safe Free-Flying Robotic Spacecraft Operations in Tumbling Target Capture
Robotics
Summary
Capturing a tumbling spacecraft safely is challenging because the target keeps spinning unpredictably. The authors present a new modular approach that uses control barrier functions to keep a robotic spacecraft within safe zones while it approaches, matches rotation, and grabs the target. This method breaks down the spacecraft's movements into parts, each with safety rules that adjust commands just enough to avoid problems without slowing down operations. They tested their system using a detailed space simulator and found it runs quickly and keeps the mission safe even with different spinning speeds.
What this means in practice
- •For space mission operators: Enable safe automated servicing or capture of tumbling satellites by applying modular safety filters to spacecraft controls during approach and capture phases.
- •For robotic system designers: Incorporate modular control barrier functions to ensure safe interactions between a robot arm and a moving, spinning target in low-gravity or space-like conditions.
Authors
Alexander Meinert, Peter Stadler, Niklas Baldauf, Alen Turnwald
Abstract
This paper presents a modular control barrier function (CBF) framework for safe free-flying robotic spacecraft operations during tumbling target capture. Motivated by latest ESA guidelines for safe close proximity operations, safety zones and requirements are translated into dedicated CBFs. The 13-DoF system is decomposed into translational, attitude, and robotic subsystems, each equipped with a safety filter that minimally modifies nominal control inputs in a lightweight quadratic program. The filters enforce a conical approach corridor, collision avoidance zone, attitude line-of-sight pointing, angular velocity limits, robotic joint limits, link-base collision avoidance, and actuator constraints. Dynamic coupling between subsystems is handled by treating upstream safe control commands as known interconnection inputs in the downstream safety filters, preserving modularity while supporting system-level safety. The framework is validated in an on-orbit servicing scenario, including final approach, angular rate synchronization, and tumbling target grasping, using the high-fidelity astrodynamics simulator Basilisk. Monte Carlo simulation results demonstrate runtime efficiency and operational safety for various tumbling rates.