ESA GNC Conference Papers Repository

Current and future GNC systems for exploration missions to small celestial bodies, planets and moons require an increasing level of on-board autonomy. Drivers for this increase include the lack of direct ground control because of communication delays, the operation in partly unknown environments, and the enhancement of the scientific exploitation through increased mission availability. To fulfill the increasing demand for more autonomous missions, key technologies for the GNC system have to be developed, which enable on-board intelligence, online monitoring for safety-critical operations, adaptable robust control, planning, and decision making. This paper focuses on the particular challenges of autonomous precise mobility on Small Solar System Bodies (SSSBs). The developed solutions from the research projects Astrone [1] and NEO-MAPP [2] are jointly presented. They consist of 1) vision-based navigation (VBN), 2) hazard detection and avoidance (HDA), 3) path planning and trajectory generators, fault detection isolation and recovery (FDIR), and 4) verification and validation (V&V) methods. VBN is necessary for SSSB missions because of their GPS-denied environment. Its two main functionalities are the spacecraft state estimation with respect to the target body and the generation of a geometrical map. The two functions are typically accomplished by including visual and ranging sensors in the GNC system, such as LiDARs, cameras (optical and/or infrared), and Laser Range Finders (LFRs). HDA accesses the generated map and the sensor inputs from the VBN module and selects possible new safer landing sites. It processes data obtained from the multiple sensors in order to evaluate various surface characteristics such as slope, roughness, and illumination. A decision making logic has to be established to pick the most suitable landing site. When the HDA selects a new landing site, the precomputed nominal trajectory has to be modified on-board based on the sensors information. This requires real-time capable guidance algorithms, which includes the various constraints of the GNC system and the mission operational requirements. In the safety-critical landing scenario, the GNC system has to be monitored on-board through the FDIR system for increased reliability. Lastly, all these novel autonomous functionalities have to be tested with adequate V&V methods and facilities. In the full paper, the solutions to the challenges 1) to 4) are discussed in more detail by presenting the novel GNC architectures of the two projects. Whereas the NEO-MAPP project focuses on the landing scenario, Astrone covers autonomous mobility functionalities for close surface operations. Taken together, they present a novel autonomous precise mobility on SSSBs to increase the scientific return for future missions. These technologies are not just applicable to SSSB missions, but can also be transferred to other planetary landings such as the Moon and Mars. Furthermore, traditional model-based solutions are compared to non-traditional AI-based solutions. For instance, HDA can either rely on maps generated from LiDARs using geometrical metrics or on images from cameras directly using convolutional neural networks. The applicability and pros and cons of AI solutions for each of the key technologies are discussed. [1] Martin, M., et al., “Astrone – GNC for Enhanced Surface Mobility on Small Solar System Bodies,” ESA GNC Conference 2021. [2] Caroselli, E., Belien, F., Falke, A., Curti, F. and Förstner, R., “NEO-MAPP µLander GN&C for Safe Autonomous Landing on Small Solar System Bodies”, AAS GNC 2022 Conference.