title: HERA vision based GNC and autonomy
Creators: name: PELLACANI, Andrea
name: GRAZIANO, M.
name: FITTOCK, M.
name: GIL, J.
name: CARNELLI, I.
Publisher: name: Proceedings of the 8th European Conference for Aeronautics and Space Sciences. Madrid, Spain, 1-4 july 2019
Year: 2019
Subjects: VISION BASED NAVIGATION
GNC
SIMULATION
SPACE SITUATIONAL AWARENESS
AVIONICS

description: The Asteroid Impact and Deflection Assessment mission (AIDA) is a joint mission between ESA and NASA to demonstrate the kinetic impactor technique for planetary defence. A NASA spacecraft, DART, will impact the moon of the Didymos asteroid binary system and the HERA spacecraft, from ESA, will get closer to investigate what was the effect of such impact. The HERA mission is based on the extensive work done by the Agency and European industry between 2011 and 2016 in the frame of the Asteroid Impact Mission (AIM). In order to be able to detect the slightest change to the system and better understand the effect of the impact, close proximity operations are baselined in the mission timeline. Both AIM and HERA missions share the vision of a highly autonomous system, which is necessary to allow such close proximity operations. As it is the first time that a binary asteroid system will be studied from such a short distance, it is also important to remark the value of the scientific return of the mission. In order to guarantee a high level of autonomy, the first step is to give to the Spacecraft enough on-board information to estimate its position with respect to the asteroids and, based on that estimation, to act accordingly following a preloaded sequence of commands or objectives. To achieve this requirement, a vision based GNC has been designed, which includes image processing algorithms and a navigation filter capable of processing the visual information and to get the desired estimation. The HERA GNC baseline presented here will not only use a visual camera but also several other payloads, involving data fusion with a hyperspectral/thermal camera and a laser altimeter (PALT). These additional instruments will be able to increase the robustness of the strategy: the hyperspectral/thermal imager will be able to see where the AFC is limited by shadows and phase angle issues; PALT will be able to give observability on the radial direction, which is poorly estimated in a vision based GNC (especially if the low gravity environment does not allow stable orbits and hyperbolic arcs are preferred for safety reasons). HERA close proximity operations have been investigated and the design will be consolidated by the end of Phase B1. A specific distance of 8 km is identified from a GNC driving factor. If the Spacecraft will be outside the 8km sphere centred in the main asteroid, the AFC will give a full visibility of the body and centroiding techniques can be used for the state estimation. For closer fly-bys the entire camera FoV will be covered by the asteroid and a feature tracking technique is baselined to maintain the relative state estimation. Image Processing and navigation functions have been designed taking into account this factor and a detailed designed showed its feasibility taking into account ground segment operations and pushing the validation of the on-board algorithms up to TRL 5/6 with Hardware-In-the-Loop tests. This paper will include the consolidated strategies of the vision based GNC designed for the HERA mission, together with the test campaign results. Additionally, the required future developments will be addressed.