ESA GNC Conference Papers Repository

The Don Quijote mission is a precursor mission planned by ESA aiming at the demonstration of an active mitigation strategy against the impact risk of Near-Earth Asteroids. The mission concept foresees an Impactor Spacecraft (IS) that would impact the target asteroid at high velocity (around 10 km/s) while an Orbiter Spacecraft (OS) would measure the change in the asteroid orbital parameters caused by the impact. The nature of the mission requires full autonomy of the spacecraft during the final impact phase. This phase is a challenging one for the design of the Guidance, Navigation and Control (GNC) functions. Indeed, the tight design requirements consist in a probability of successful impact better than 95% and an impact accuracy better than 50 m (3 s). The use of autonomous optical navigation at least 2 days before impact is a critical constraint which requires an efficient navigation algorithm. The navigation function is required to estimate the spacecraft position and velocity relative to the moving impact point autonomously using only an optical device and knowledge of its initial states at the beginning of the impact phase. Then, the guidance is required to compute manoeuvres while ensuring the observability of the relative states and the proper reduction of the distance to target in the B-plane. These two requirements are contradictory since observability requires target drifting in the B-plane while impact success requires keeping the target in the centre of the B-plane frame. The attitude control is more conventional but requires a high stability performance in order to keep accurate pointing during thrusting. In this context, this paper focuses on the design and analysis of the Impactor innovative GNC algorithms developed in the framework of an ESA phase A study for the final impact phase. First, this paper presents the general spacecraft architecture with emphasis on the challenging design of the propulsion system layout. Then, it explains the analyses performed to select the navigation camera. Aslo addressed is the selection of the line-of-sight measurements-based navigation algorithms required to estimate the necessary correction DV to reduce the targeting error. Finally, different candidate guidance algorithms are presented. In order to validate the GNC algorithms, they have been integrated into a nonlinear simulator and tested by a Monte-Carlo campaign taking into account scattering on initial conditions, on initial state knowledge and on other critical parameters.