Trajectory Recovery and Terrain Reconstruction Based on Descent Images under Dual-Restrained Conditions: Tianwen-1

Chen Qi,Aigong Xu,Yongzhe Yan,Youqing Ma,Shaochuang Liu,Jianli Zhang,Xinchao Xu,Huan Yang,Yaming Xu,Minglei Li

doi:10.3390/rs14030709

Abstract

Tianwen-1 is the first Mars probe launched by China and the first mission in the world to successfully complete the three steps of exploration (orbiting, landing, and roving) at the one time. Based on the unverifiable descent images which cover the full range of the landing area, trajectory recovery and fine terrain reconstruction are important parts of the planetary exploration process. In this paper, a novel trajectory recovery and terrain reconstruction (TR-TR) algorithm employing descent images is proposed for the dual-restrained conditions: restraints of the flat terrain resulting in an unstable solution of the descent trajectory and of the parabolic descent trajectory causing low accuracy of terrain reconstruction, respectively. A landing simulation experiment on a landing field with Mars-like landform was carried out to test the robustness and feasibility of the algorithm. The experiment result showed that the horizontal error of the recovered trajectory didn’t exceed 0.397 m, and the elevation error of the reconstructed terrain was no more than 0.462 m. The algorithm successfully recovered the descent trajectory and generated high-resolution terrain products using in-orbit data of Tianwen-1, which provided effective support for the mission planning of the Zhurong rover. The analysis of the results indicated that the descent trajectory has parabolic properties. In addition, the reconstructed terrain contains abundant information and the vertical root mean square error (RMSE) of ground control points is smaller than 1.612 m. Terrain accuracy obtained by in-orbit data is lower than that obtained by field experiment. The work in this paper has made important contributions to the surveying and mapping of Tianwen-1 and has great application value.

Highlights

This paper presents the work of obtaining the position and pose information of the landing camera and reconstructing the terrain of the landing area
Comparison of the refined motion of selected images after bundle adjustment using feature feature points extracted by the methods of this paper and Scale-invariant feature transform (SIFT). (a) Comparison of normalized points extracted by the methods of this paper and SIFT. (a) Comparison of normalized horizontal horizontal error. (b) Comparison of pitch error. (c) Comparison of roll error. (d) Comparison of error.yaw (b) error
The terrain condition in the landing area leads to the inability to calculate the motion of the landing camera robustly, and the forward motion of the landing camera along the parabolic trajectory leads to the inability to reconstruct the accurate terrain

Summary

Introduction

Planetary exploration began in the 1950s, developed to launch various planetary probes in the late 1980s, and entered a new era of planetary exploration with the help of the computer and other technologies by the beginning of the 21st century [1]. The moon and Mars are the primary targets for exploration [2]. China was a late starter in planetary exploration, the series of missions from Chang’e-1 to Chang’e-5 marked the success of the three-step mission of “around, down, and back”. In the lunar exploration project [3,4,5]. In addition to the lunar exploration project, Mars 4.0/).

Methods

Discussion

Conclusion