Performance of a Crater Navigation Method for Lunar South Pole Landing

Abstract

Many future missions are aiming to land at, or close to, the lunar south pole - an immensely challenging landing site. It provides very challenging illumination conditions and is defined by very rough terrain. Landing in such a terrain will call for precision navigation abilities, a feature not only required by future missions aiming for the poles but also by others. Precision navigation can be enabled by including an absolute navigation system into the landing suite. In this paper one such absolute navigation method is presented: CNav, a vision based crater matching method. CNav can detect and match craters using on-board images and can thereby enable precision navigation. CNav’s crater catalogs are based on a database of more than 40 million craters, which can be further enhanced for the landing site location. A detailed analysis of the illumination conditions at the south pole has shown that the illumination conditions are very challenging, but possible mission timeliness and trajectories exist that satisfy CNav’s operational needs. One of these has been selected, and the images that a lander would acquire during this mission have been rendered using digital elevation models of the Moon. Using this data, it has been demonstrated that CNav can be operated successfully during a south pole landing approach until approximately 1 km above the landing site. CNav can provide frequent solutions at about 1 Hz, provided that the terrain seen by the camera allows for it, i.e., is not shaded and contains craters.