Challenges of Pinpoint Landing for Planetary Exploration : the Lion Absolute Vision-based Navigation System Step-wise Validation Approach

After ExoMars in 2016 and 2018, future ESA missions to Mars, the Moon, or asteroids will require safe and pinpoint precision landing capabilities, with for example a specified accuracy of typically 100 m at touchdown for a Moon landing. The safe landing requirement can be met thanks to state-of-the-art Terrain-Relative Navigation (TRN) sensors such as Wide-Field-of-View vision-based navigation cameras (VBNC), with appropriate hazard detection and avoidance algorithms. To reach the pinpoint precision requirement, on-board absolute navigation with respect to the landing site is mandatory, with a typical accuracy better than 100 m at touchdown for a Lunar mission, or below 10 km at entry interface for a Mars landing missions. In this paper, we present the validation approach and experimental results of an Absolute Visual Navigation system (AVN) known as Lion. The Lion functional architecture will be first presented, as well as the implemented incremental validation and verification approach ; experimental set-up and end-to-end tests results will be summarized. Finally, way forward and lessons learned will be discussed.