Visual Localization of the Tianwen-1 Lander Using Orbital, Descent and Rover Images

Wenhui Wan,Tianyi Yu,Jia Wang,Man Peng,Runzhi Wang,Zheng Bo,Meiping Yang,Lejia Ye,Zhaoqin Liu,Bin Liu,Lichun Li,Kaichang Di,Yexin Wang,Li Yin,Shuo Bao,Zuoyu Zhang,Ke Shi,Hui Zhang,Xiufeng He ,Hao Lü

doi:10.3390/rs13173439

Abstract

Tianwen-1, China’s first Mars exploration mission, was successfully landed in the southern part of Utopia Planitia on 15 May 2021 (UTC+8). Timely and accurately determining the landing location is critical for the subsequent mission operations. For timely localization, the remote landmarks, selected from the panorama generated by the earliest received Navigation and Terrain Cameras (NaTeCam) images, were matched with the Digital Orthophoto Map (DOM) generated by high resolution imaging camera (HiRIC) images to obtain the initial result based on the triangulation method. Then, the initial localization result was refined by the descent images received later and the NaTeCam DOM. Finally, the lander location was determined to be (25.066°N, 109.925°E). Verified by the new orbital image with the lander and Zhurong rover visible, the localization accuracy was within a pixel of the HiRIC DOM.

Highlights

Tianwen-1, China’s first independent Mars exploration mission, was launched fromWenchang Space Launch Center in Hainan province by the Long March-5 heavy-lift carrier rocket on 23 July 2020 (UTC+8) [1]
To decrease the localization error caused by the slight offset between the descent camera and the center of the lander, the Navigation and Terrain Cameras (NaTeCam) Digital Orthophoto Map (DOM), produced by the images captured with a pitch angle of −30°, was employed to refine the landing position from the matching of the lowest descent image and the base map
To achieve the accurate landing location in a timely manner, the remote landmarks found in the earliest received NaTeCam images were identified in the orbital DOM of the landing area to conduct the landmark triangulation-based lander localization

Summary

Introduction

Tianwen-1, China’s first independent Mars exploration mission, was launched from. Wenchang Space Launch Center in Hainan province by the Long March-5 heavy-lift carrier rocket on 23 July 2020 (UTC+8) [1]. The downlinked single descent image covered a very small area and has a highly different ground resolution (about 0.05 m/pixel) with the orbital DOM (0.7 m/pixel). It was ground resolution (about 0.05 m/pixel) with the orbital DOM (0.7 m/pixel). The remote landmarks, found in NaTeCam images in horizontal view angle, were were identified in the orbital DOM and used to triangulate the lander position as the identified in the orbital DOM and used to triangulate the lander position as the initial initial localization result. The NaTeCam DOM of landing site was taken to determine the lander location by DOM matching with descent the landing was taken to determine theproposed lander location images. 2 shows the workflow of our method.by DOM matching with descent images.

Data and Methodology

Initial Localization Based on Landmark Triangulation

Refined Localization Based on Image Matching

Results

Verification

Conclusions