How does the five-star red flag of Tianwen 1 unfold on Mars

　　On June 11, the National Space Administration held the unveiling ceremony of the first batch of scientific image maps of the Tianwen-1 rover landing on Mars, and announced the panoramic view of the landing site, the topography of Mars, the “Chinese Imprint” and the “Chinese Imprint” taken by the "Zhurong" rover. Photographs such as a group photo with a tour.

The release of these scientific image maps marked the complete success of my country's first Mars exploration mission.

　　In the two images of "Chinese Imprints" and "Photographs of the Tour", the bright red and square Chinese flag is clearly visible.

The Chinese flag locking and deployment mechanism independently designed and developed by the team of Professor Leng Jinsong of the School of Astronautics of Harbin Institute of Technology. After 202-day-to-earth-fire transfer and 93-day orbital detection, after flying 475 million kilometers, it will be in Tianwen on May 15, 2021. The successful completion of the controllable and dynamic deployment of the Chinese flag on the No. 1 lander made my country the first country in the world to apply shape memory polymer smart structures to deep space exploration projects.

　　In the early 1990s, under the guidance and support of Academician Du Shanyi, the Institute of Composite Materials and Structures, School of Aerospace, Harbin Institute of Technology, established the research direction of smart materials and structures earlier in China.

Under the guidance of the development concept of "Integration of Science and Engineering, Serving Aerospace", Professor Leng Jinsong's team has intensively cultivated and made innovations in the research fields of intelligent structural mechanics, design and its aerospace applications.

The team took the lead in developing a series of Shape Memory Polymer (SMP) such as epoxy group, cyanate ester group and polyimide group with independent intellectual property rights in China. The glass transition temperature is adjustable (37℃). -322℃), to meet the requirements for use in extremely harsh environments.

　　According to the overall mission requirements of the Tianwen-1 Mars exploration mission, the team of Professor Leng Jinsong, supported by the China Academy of Space Technology, is based on shape memory polymer composites with independent intellectual property rights, through fine mechanical theoretical analysis and ingenious intelligent structures Designed and successfully developed a locking and unfolding mechanism for the Chinese flag.

　　It took more than 9 months for Tianwen-1 from launching into orbit to landing on Mars. The detection risk is high and difficult. The flag-locking and deployment mechanism faces challenges such as the interplanetary space environment, the thin atmosphere of Mars, and the Martian wind. At the same time, there are problems in the landing environment. Difficulties such as determination and inability to intervene on the ground put strict requirements on the reliability of the product.

"By simulating the mechanics, thermal vacuum, thermal cycle, and locking and unfolding functions of the Martian environment, we have repeatedly iteratively tested and verified in extreme environments. We have innovatively designed and prepared a winding lock-unfold mode flag locking and unfolding mechanism for the landing platform. The deployment process of the national flag is similar to the deployment method of traditional Chinese calligraphy and painting, which solves the key technical problems of long-term lock-in, low-impact and reliable deployment under extremely harsh operating environments such as low temperature and irradiation." Leng Jinsong said.

　　According to Leng Jinsong, before landing on Mars, the flag locking and unfolding mechanism is in a coiled storage state, and long-term locking is achieved through a shape memory polymer composite structure.

After landing on Mars, the ultra-low impact unlocking and controllable deployment are achieved by heating the shape memory composite material, and the five-star red flag (developed by the Lanzhou Institute of Space Technology Physics) is released and deployed.

After unfolding, the stiffness of the shape memory polymer composite material returns to a level equivalent to that of the conventional composite material, providing a high-rigidity load-bearing function.

Compared with the way of carrying the national flag, such as mounting, folding, storing and unfolding, the self-designed and developed national flag locking and unfolding mechanism is lighter in weight and higher in storage ratio, and can be applied to larger-sized national flags.

Compared with the deployment structure based on pyrotechnics, which has a transient impact of more than 10,000g, the flag locking and deployment mechanism has almost no impact.

　　The flag locking and deployment mechanism developed by the team realized the controllable and dynamic deployment of the Chinese flag on Mars for the first time. After the deployment, the five-star red flag fluttered in the wind bathed in the Martian wind, marking the Chinese probe on Mars with the "Chinese logo" and building the party. 100th anniversary gift.

　　It is reported that this is the first international realization of shape memory polymer after the successful verification of shape memory polymer composite material and its flexible solar cell system in the geosynchronous orbit environment by the scientific research team of Harbin Institute of Technology in 2016 and 2020. The application of smart structures in Mars exploration projects indicates that my country is in the forefront of the world in the field of smart materials and their applications in spacecraft structures.

　　In the future, related technologies such as smart structures based on shape memory polymer composites are expected to be applied to my country's space stations, lunar exploration projects, manned lunar landings, Mars exploration, Jupiter exploration, asteroid exploration, ice giant exploration, deep space exploration and other major aerospace Engineering also has broad application prospects in the fields of aerospace, aviation, automobiles, high-end equipment, intelligent manufacturing, robotics and biomedicine.

(Our reporter Zhang Shiying)