A Phased Landmark Navigation Method for Lunar Exploration

This paper proposes a phased landmark navigation method for the pinpoint landing problem during lunar exploration, which divides the navigation process into two phases: control landmarks phase and random landmarks phase. The control landmarks are ground markers containing terrain information extracted from the topographic map of the known landing area, and the random landmarks are image markers extracted between successive images of the spacecraft. In the control landmark phase, the control landmarks are matched with the images taken during the spacecraft landing for localization. To ensure that the control point positions on each landing image frame are extracted accurately, this paper first passes the position of the control points between adjacent frames by homograph transformation and splits small template images near the positions to match the template images with the control landmarks for template matching and search for the sub-pixel image point positions. The last landing image that can match with the control landmarks is used as the reference map in the random landmarks phase, and Harris feature points are extracted on the subsequent landing images to make random landmarks and then matched with the reference map for positioning. Finally, the method is verified using the images taken by Chang’e-4 landing camera and the terrain data of 5m resolution in the landing area. The experimental results show that this method can effectively increase the working range of visual navigation and achieve a pinpoint landing accuracy of about 10m at the same time.