A Map Relative Localization System for Planetary Landing

The Mars 2020 Entry Descent and Landing (EDL) system successfully delivered the Perseverance rover to the surface of Mars on February 18th, 2021. A large fraction of the 8km wide Jezero Crater landing ellipse is covered with landing hazards including cliffs, inescapable dune fields and rocks. To mitigate the risk of these hazards, a novel Terrain Relative Navigation system was developed and integrated with the heritage Mars Science Laboratory EDL system. First the hazards were identified or inferred using orbital imagery and stored on-board the spacecraft as a hazard map. During parachute descent, the Lander Vision System (LVS) estimated map relative position by fusing landmarks matched between descent imagery and a map of the landing site with inertial measurement unit data. This position estimate and the hazard map were used by the powered descent guidance and control system to identify and then fly to the safest target for landing that was also reachable given fuel and other constraints. Post-flight analysis indicated that the horizontal error between the targeted location and actual landing location was 5m relative to a 60m requirement, which indicated that all required systems worked much better than designed. In particular, the fully autonomous LVS generated a position estimate in 10s that was in error by only a few meters relative to a 40m requirement. This paper describes the LVS design, how it was tested before launch and the LVS performance during EDL.