  This paper proposes a Guidance, Navigation, and Control (GNC) architecture
for planetary rovers targeting the conditions of upcoming Mars exploration
missions such as Mars 2020 and the Sample Fetching Rover (SFR). The navigation
requirements of these missions demand a control architecture featuring
autonomous capabilities to achieve a fast and long traverse. The proposed
solution presents a two-level architecture where the efficient navigation (low)
level is always active and the full navigation (upper) level is enabled
according to the difficulty of the terrain. The first level is an efficient
implementation of the basic functionalities for autonomous navigation based on
hazard detection, local path replanning, and trajectory control with visual
odometry. The second level implements an adaptive SLAM algorithm that improves
the relative localization, evaluates the traversability of the terrain ahead
for a more optimal path planning, and performs global (absolute) localization
that corrects the pose drift during longer traverses. The architecture provides
a solution for long range, low supervision and fast planetary exploration. Both
navigation levels have been validated on planetary analogue field test
campaigns.
