ESA GNC Conference Papers Repository

This paper discusses the challenges of navigating in close-proximity of an asteroid of diameter < 300 m, which is at the small end of the NEO population. Such objects are of current research interest since they are likely candidates for the next major Earth impactor and gained an increasing interest by the asteroid mining community. An autonomous near-inertial controlled hovering AOCS/GNC mode designed by Airbus Defence & Space in Friedrichshafen in Germany, appropriate for typical research goals like momentum enhancement factor determination in such a low gravity environment is presented. Stable close-proximity observation is challenging due the inherent high perturbations-gravity acceleration ratio near such small bodies. Therefore, the state-of-the-art hyperbolic flyby's or terminator orbits, flown by the Rosetta and OSIRIS-REx spacecraft that are governed dominantly by the gravitational pull of the body do not guarantee a stable motion anymore. The proposed spacecraft GNC architectural design and the on-board GNC/AOCS algorithms are built upon a landmark based pose estimation technique using a single mono camera . The sensitivity of the spacecraft dynamics predictions to thruster errors, solar radiation pressure, reaction wheel offloading manoeuvres and to the accurate mathematical model or digital terrain map of the asteroid's shape is shown. The relative spacecraft navigation errors and operational GNC performance is demonstrated via closed-loop simulations where image processing algorithms are stimulated using synthetic images generated with the Planet and Asteroid Natural scene Generation Utility (PANGU). Performance results are discussed for a simulated reference scenario where an orbiter spacecraft operates at close proximity of the Near-Earth Object 2001 QC34 (d=230 m, a\b elongation ratio = 1.4). The presented concept is directly applicable to the OSIRIS-REx and AIDA/AIM mission but also to future missions targeting even smaller asteroids.