— In this paper, multiple on-board sensors are used to assess the terrain safety in real-time during spacecraft descent. A linguistic, fuzzy rule-based reasoning engine is used to determine terrain safety from sensor measurements and, together with information about required fuel consumption and site science return, provide a figure-of-merit for all possible landing sites. Additional fuzzy rule-sets are used to address spatial and temporal dependence in the reasoning process in order to arrive at a final score for each potential landing site. This landing score is used to retarget the spacecraft if the original landing site is found to be hazardous. Simulation studies are presented for illustration.