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.
The spacecraft for the Tianwen-1 probe comprises an orbiter, a lander and the Zhurong rover, aiming to complete orbiting, landing and roving in one single mission, which is the first such attempt in global aerospace history. The mission aims to obtain scientific exploration data on the Red Planet, and currently, Tianwen-1 has completed orbiting Mars and has successfully landed on a pre-selected landing region on the Utopia Planitia of Mars. The Mars rover Zhurong is also due to begin Martian exploration.
Dr LAM Tai-fai, Chairman of Council, PolyU, offered his warmest congratulations to the Nation on the successful soft landing of Tianwen-1. He said, “The Nation has developed an impressive track record in deep space exploration, such as its lunar exploration and lunar sample return missions. This time the Nation begins its planetary exploration journey by setting its sights on Mars for the first time, which further cements China’s advanced space capabilities. We are immensely encouraged that PolyU played a pivotal part in facilitating the Tianwen-1 mission. With extraordinary creativity, perseverance and innovative minds, our researchers will continue to contribute to the well-being of mankind in various scientific fields.”
Mr Alfred SIT, Secretary for Innovation and Technology of the HKSAR Government, said, “I would like to extend my heartfelt congratulations to our Nation on the successful landing of the Nation’s first Mars exploration project. Basic research is the strength of local universities, and the fact that PolyU was invited to participate in another major national space mission with its scientific research capabilities is a clear demonstration of Hong Kong’s exceptional strength in research and innovation. Hong Kong is also a place where many hidden talents emerge, forming an important force in national technological advancement. They will contribute to the Nation’s ‘Megascience’ projects with their expertise. I hope that local universities take advantage of research collaboration opportunities with institutions in the Mainland to create synergies that bring about complementary advantages.”
Professor Jin-Guang TENG, PolyU’s President, said, “We sincerely thank our Nation for trusting PolyU and inviting two of our Professors to participate in this national Mars exploration project. We are proud to have the opportunity to once again contribute to a major national aerospace technology mission. Leveraging the achievements of PolyU in the field of aerospace technology, we have decided to increase our support in this area by establishing the University Research Centre for Deep Space Explorations led by Professor Yung Kai-leung. We aim to pool together experts in different fields such as Geology, Architecture, Machinery, Physics, and Remote Sensing to conduct in-depth research in different aspects of aerospace technology. We truly hope that the mission of Tianwen-1 will be a great success and that the world will learn more about the Red Planet.”
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.
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.”
Mars Landing Surveillance Camera (Mars Camera)
With a wealth of experience in developing sophisticated space instruments, Professor Yung Kai-leung, PolyU’s Sir Sze-yuen Chung Professor in Precision Engineering, Chair Professor of Precision Engineering and Associate Head of Department of Industrial and Systems Engineering, has led a team to undertake the research, design and manufacturing of the Mars Camera since 2017. Thanks to their dedication and perseverance, as well as the support of the University, the team successfully completed and delivered the Mars Camera with the corresponding space qualification experiments in less than three years.
The PolyU-developed Mars Camera is located on the outside top surface of the lander platform, for monitoring the landing status, the surrounding environment of Mars and the movements of the Zhurong rover with respect to the unfolding and status of the solar panels and antennae. This information is critical for the successful movement of the Mars rover on the surface of Mars.
The Mars Camera is light in weight (around 390g), yet strong and durable enough to withstand the extreme temperature differences of about 150 degrees Celsius experienced during the nine-month journey between Earth and Mars, followed by immediate operation under the extremely low temperatures on the surface of Mars. As the Mars Camera is designed for the lander, it also has to withstand huge impact shocks of 6,200G (i.e. 6,200 times the force of Earth’s gravity). Despite having a wide-angle field of view (a maximum of 120 degrees horizontally and a maximum of 170 degrees diagonal), the Mars Camera has low image distortion.
Professor Yung explained, “To capture ultra-wide angle images on Mars for scientific research, the Mars Camera has to have a wide field of vision with low distortion optics within the little allowable payload, but at the same time must also be able to withstand extreme temperature variation, high radiation, mechanical impact and vibration within the little available mass, whereas maintaining high reliability under the extreme space travel environment such as high radiation.”
Professor Yung further shared that he was relieved that the PolyU-developed Mars Camera survived the Earth to Mars journey, “It was a real thrill when we learned that Tianwen-1 successfully touched down onto the Martian surface. A photo recently released by the China National Space Administration shows our Mars Camera on the Red Planet, and I am particularly excited to observe from the photo that our Camera remains intact. I look forward to seeing our Mars Camera capturing the spectacular views of Mars and providing images of the unfolding and movement of the Zhurong rover.”
「天問一號」探測器由環繞器、著陸器和巡視器 (又名「祝融」火星車) 組成，目標是一次過完成「繞、落、巡」(即「環繞」、「著陸」和「巡視」)三大工作，是世界航天史上的首次嘗試；這次任務旨在獲取有關火星的科學勘探數據。目前，「天問一號」已完成火星軌道環繞及著陸預選著陸區烏托邦平原，「祝融」火星車正侍機展開巡視及勘探工作。
「天問一號」自2021年2月10日進入環火軌道後，已收集並傳回大量覆蓋目標著陸區的亞米級高解像度圖像回地球。是次任務的目標著陸區面積達70公里 x 180公里，即比整個香港的面積大11倍。吳波教授及其團隊利用自行研發的「三維集成測量模型」，將「天問一號」傳回的高解像度圖像，製成高精確度、高解像度的三維數碼地形模型，以詳細分析地形特徵，識別可能影響著陸安全的大型斜坡。
[From PolyU Media Release]
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