ESA GNC Conference Papers Repository
Design and validation of a GNC system for missions to asteroids - the AIM scenario
The Asteroid Impact Mission (AIM) is a small ESA mission of opportunity which has the goal to demonstrate and consolidate new technologies for future exploration missions to asteroids, to perform scientific observations of a binary asteroid system (Didymos) and to assess planetary defence capabilities in the context of the AIDA program, in collaboration with NASA. The AIM main spacecraft is designed to carry and deploy three smaller spacecraft - the MASCOT-2 asteroid lander, provided by DLR, and two CubeSats (COPINS). To operate all the payloads on-board the spacecraft, to perform the science experiments and to obtain valuable data of the binary system, it is mandatory to perform operations in close proximity to the asteroids. This imposes significant challenges on the GNC subsystem in terms of performance and reliability, especially considering that some level of autonomy is needed for such operations. In particular, the release of the MASCOT-2 lander and COPINS cubesats and the execution of the RSE (Radio Science experiment) will require a relative distance to the binary system in the order of hundreds of meters. For this reason, a vision based GNC has been designed and validated in the GMV facilities. This vision based GNC will rely only on star trackers, IMU and a navigation camera (AIM Framing Camera - AFC, provided by the Max Planck Institute) to track unknown features on asteroid surfaces. The in-house heritage acquired in the frame of the Marco Polo / Marco Polo - R missions has been re-used to the maximum possible extent and has been consolidated in the frame of the AIM project adapting the strategy to a fly-by approach that guarantees always collision free trajectories. The validation of the algorithm has been performed at MIL (Model in the loop) level, including the PANGU image generator to test the feature tracking image processing used for relative navigation. Thanks to the qualification model of the AFC available at GMV, also HIL (Hardware in the loop) tests have been performed, both in the optical lab and in the robotic facility of GMV, the <i>platform-art</i>. This paper describes the design and validation of the precise and robust GNC for relative navigation with respect to the Didymos asteroid including the solutions used at FDIR level to ensure safety (e.g. Collision Avoidance Manoeuvre triggering). This autonomous GNC subsystem achieves the safety requirements of the AIM mission and at the same time guarantees relative distances to the body that could not be achieved by operating the spacecraft from ground.