Two research teams at The Hong Kong Polytechnic University (PolyU) contributed to the Nation’s first Mars exploration project Tianwen-1. By harnessing their extensive experience in the field of aerospace science and technology, as well as their commitment to research excellence, PolyU researchers played a vital role in the Tianwen-1 mission, in collaboration with the China Academy of Space Technology (CAST). Professor WU Bo helped identify possible landing regions with advanced topographic mapping and geomorphological analysis technologies. Professor YUNG Kai-leung developed a sophisticated space instrument, the “Mars Landing Surveillance Camera (Mars Camera)”, for capturing images of the surroundings of the Red Planet and monitoring the status of the Zhurong Mars rover.
Mars landing site mapping and evaluation
Landing on Mars is a challenging endeavour due to several reasons, such as the complicated Martian surface, the very thin atmosphere as well as possible dust storms. There is also a 5-20 minutes time delay between Mars and Earth communications. It is therefore of paramount importance to select a landing site that is safe and of scientific significance.
From 2017-2020, upon invitation by CAST, Professor WU Bo from PolyU’s Department of Land Surveying and Geo-Informatics led a team to carry out global-scale analysis and evaluation to help shortlist three candidate landing regions, namely the Amazonis Planitia, Chryse Planitia, and Utopia Planitia, that are all located within a latitude ranging from 5° - 30°N on Mars. These regions have adequate solar illumination for optimised power generation and moderate temperature, lower elevation for longer deceleration time, and a flat terrain surface for safe landing.
The team further conducted detailed topographic and geomorphological mapping and analysis of the candidate landing regions, including their elevations, slopes, rock abundances, crater densities, and geological contexts. As a result of the evaluation, a region in the southern Utopia Planitia, the largest recognised impact basin in the northern hemisphere of Mars, was selected as the target landing region. Some features in the Utopia Basin like extensive sedimentary materials on the surface have been interpreted as morphological indicators of potential water-ice underneath, which are of great scientific interest since they may offer new insights into the existence of life on Mars and the evolutionary history of the Red Planet.
Since entering the orbit of Mars on 10 February 2021, the Tianwen-1 probe has collected and sent back a large quantity of sub-meter-resolution images of the target landing region covering an area of about 70km × 180km, which is about 11 times larger than the size of Hong Kong’s territory. Using the high-resolution images from Tianwen-1, Professor Wu and his team generated high-resolution and high-precision 3D digital topographic models of the target landing region using the self-developed integrated 3D mapping model, to analyse the detailed topography and identify large slopes hazardous for landing.
To facilitate safe landing and roving on Mars, Professor Wu’s team also developed AI-based techniques for more automated and robust analysis of geomorphological features like craters and rocks from the high-resolution images in a short period of time. Professor Wu said, “With the aid of the AI-based techniques, we analysed over 670,000 craters, over two million rocks, and hundreds of volcanic cones distributed over the target landing region in 1.5 months. We achieved much higher efficiency in the automatic extraction of rocks and craters with about 85% correctness.” From the topographic and geomorphological mapping results, the team successfully identified several landing ellipses for the mission management team to finalise the landing site.
hazard map:
Professor Wu felt very honoured to be able to participate in and contribute to the Nation’s Mars exploration project. He said, “The Tianwen-1 mission is a mega project, and we are only a small part of an effort of thousands of people, to support the accomplishments of the mission. All of my team members were fully dedicated to the undertaking over the past months. I am thankful to them for working around the clock to get the task completed on time, yet without comprising accuracy and details.”
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