Autonomous GNC systems are one of the enabling technologies for many of the future ESA exploration
missions. One of those innovative missions is an asteroid sample return mission aiming at small (<1 km) near-
Earth asteroids. During the proximity, landing and sampling (PLS) operations, the GNC system will be
challenged by some critical factors, namely (1)the extremely tight requirement on the landing accuracy of few
metres (3-sigma), (2)the large uncertainties in the asteroid characteristics that define the dynamics during the
PLS operation, (3) the weak gravity field creates a small sphere of influence where the orbits around the
asteroid are strongly perturbed by the solar radiation pressure, the Sun third body effect and the irregularities
of the asteroid gravity field, (4) cost and technological limitations also constrain the selection of the navigation
sensor suite and the GNC strategy. The design of possible autonomous GNC solutions will be presented for
different proximity operations phases. The proximity operations shall considering the realistic a priori
knowledge, the ground involvement and the on-board autonomy periods. High-fidelity simulations will provide
the performances of the GNC systems in the different phases of the NEO proximity and landing operations
