Design and Verification of Multi-Functional Obstacle Avoidance Sensor for the Tianwen-1 Mars Probe.

China's first Mars probe, the Tianwen-1, successfully landed on the Martian Utopia Plain on May 15, 2021. The multi-functional obstacle avoidance sensor (MOAS) has been the key navigation equipment for the entry, descent, and landing (EDL) operation of Tianwen-1. The MOAS integrates a landing camera and a laser imaging module and can acquire sequential optical images of the landing process of Tianwen-1 and high-resolution topography of the Martian surface. As a navigation sensor, the MOAS plays a key role in the processes of back cover avoidance, coarse obstacle avoidance, and hovering fine obstacle avoidance from the height of 10 km to landing. The MOAS's laser imaging module uses a new-generation scanning component, a two-dimensional MEMS scanning mirror, which is a unique feature compared to other space lidars. In this paper, optical and electronic designs of the MOAS are analyzed in detail. Based on the open-loop control feature of a MEMS scanning mirror, an online training and calibration method is proposed to increase the accuracy of optical angle control to 0.02°. In addition, the ground performance validation and the space environment testing of MOAS are described in detail. The inflight performance of MOAS is evaluated based on the sequential camera images and 3D point cloud data. In addition, the MOAS combines the attributes of a scientific instrument. The images obtained by the sensor can reconstruct the descending trajectory of Tianwen-1, determine accurate landing coordinates, and acquire information on the topography, surface reflectivity, and sand and dust of Mars. [ABSTRACT FROM AUTHOR]