Wu Bo (first right), an associate professor of the Hong Kong Polytechnic University's Department of Land Surveying and Geo-Informatics, stands with his Chang’e-4 project team at China Academy of Space Technology in Beijing on Jan 4, 2019. (PHOTO PROVIDED TO CHINA DAILY)
A Hong Kong-based scientific team attributed their accomplishment of assisting the nation to land its first Mars rover in May to a full cooperative spirit.
The 20-member team of Hong Kong Polytechnic University had been racing against the clock for six weeks, from mid-March to early May, to find an ideal landing site for the lander/rover portion of the Tianwen-1 probe.
They were mainly graduates, doctoral and postdoctoral students of the Department of Land Surveying and Geo-Informatics, led by Wu Bo, associate head (research) and professor of the department.
The 20-member team, at the invitation of the China Academy of Space Technology, joined China’s first Mars exploration mission when it was launched in 2016.
Wu’s team stood out during the mission with its innovative topographic mapping and geomorphological analysis techniques, and experiences. They had helped with mapping and evaluating landing sites on the moon for China’s Chang’e-4 lander in 2019 and the Chang’e-5 lander in 2020. The latter also carried back to Earth lunar surface samples for the first time in 44 years.
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This time, they were responsible for analyzing the safest site on Mars to land a spacecraft. Such a site needed to be the flattest area with the gentlest slope.
Their suggestion could make or break the mission to the red planet as ground control is impossible during the landing, as the distance between Earth and Mars make it impossible to control the spacecraft’s descent in real time via radio signals. The event was described as “nine minutes of terror”.
Their major worry was the tight time schedule. The Hong Kong team was given a clear deadline – they had only about six weeks to conduct a thorough survey of an initial targeting landing zone of 12,600 square kilometers, which is 11 times the size of Hong Kong, or two-thirds that of Beijing. The image files and data piled up reached 100 gigabytes.
Racing against time, the entire team worked as if it was in a relay race. “Everybody was forever ready to answer calls” and to take over the work, said Wang Yiran, a PolyU postdoctoral fellow and one of the team members.
Racing against time, the entire team worked as if it was in a relay race. “Everybody was forever ready to answer calls” and to take over the work, said Wang Yiran, a PolyU postdoctoral fellow and one of the team members
To reduce interference of the Martian atmosphere in the images, Morgan Liu Wai-chung, another postdoctoral fellow in Wu’s team, improved his expertise in the shape-from-shading algorithm. It reconstructed the 2D images it received into three-dimensional models to reproduce the scene of the Martian surface despite atmospheric interference.
But he had to act quickly and deliver his work as early as possible to free up more time for the rest of the team. During the mission, Liu slept only four hours a day, the least among the team members.
The due date finally arrived. Based on the data from the students, Wu recommended to Beijing three safest oval-shaped areas within the targeting landing zone. Beijing settled for area No 16 — the least-risky one found by the team. It signaled the team had accomplished its mission.
The Hong Kong research team’s findings were later turned into reality with the Tianwen-1 lander had ending up landing right near the center of the area No 16 in the early morning of May 15. The coordinates of the landing site were 25.1 degrees north and 109.9 degrees east.
It made China the second country after the United States to land and operate a rover on Mars.
“The Tianwen-1 mission is a mega project, and we’re only a small part of the efforts of thousands of people, in supporting the mission’s accomplishments. All of my team members were fully dedicated to the undertaking over the past months,” Wu said.
“We’re not only witnessing history, we’re part of history,” he added.
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The spirit of collaboration shined not only within the team, but throughout the project, which attracted thousands of the country’s best scientists and technicians. Along with Wu’s team, another PolyU team, led by Professor Yung Kai-leung, associate head of the Department of Industrial and Systems Engineering, had developed a surveillance camera fixated on the Tianwen-1 lander. It was set to monitor the landing and photograph the surrounding Martian environment.
The 390-gram device — the equivalent of two iPhone 11s — would have to withstand an impact force of about 6,200 times the force of Earth’s gravity. “I’m so glad it did not break into parts”, Yung said in jest at a news conference in May celebrating the event.
Cherishing these memories of this spring on Earth, the young scientists have resumed their normal campus lives. But a goal was planted in their heart, for the next opportunity to contribute to another ambitious national space project, such as China’s explorations of the near-Earth asteroids scheduled in the next five years, or collecting samples from Mars in a decade’s time.