On December 1, 2020, the Chang'e-5 probe landed steadily and softly in the area north of the Lumke Mountains, a frontal storm on the moon, and the laser ranging velocimetry sensor and laser three-dimensional imaging sensor developed by the Shanghai Institute of Technical Physics of the Chinese Academy of Sciences (hereinafter referred to as the "Shanghai Institute of Technology") played an important role in the process of setting the moon.
"Continents carry out lunar and deep space exploration, one is to take pictures, the second is to go to a strange planet to actually know its geological structure first, which is a basic investigation." Shu Rong, deputy director of Shanghai Institute of Technology, was recently introduced in an interview with CBN.
Active optoelectronic technology mainly uses laser interaction with the target to accurately obtain target distance, speed, three-dimensional morphology, spectral characteristics, etc. Not only the Chang'e series of lunar probes, but also the major engineering and scientific tasks such as the Tianwen-1 Zhurong Mars Rover, the Quantum Science Satellite, and the Gaofen-7 Satellite, are inseparable from the active optoelectronic instruments developed by Shanghai Technology, and behind these key autonomous technologies is the space active photoelectric payload development team with an average age of less than 40 years old.
Since 2002, the team has undertaken the task of developing scientific and engineering payloads from Chang'e 1 to No. 5, developed a series of rangefinders, speed sensors, laser three-dimensional imaging sensors, etc., key technologies are independent and controllable, and the self-developed scheme proves China's ability to achieve accurate obstacle avoidance of landers on the lunar surface, and has won the first prize of National Science and Technology Progress Award, the Outstanding Achievement Award of the Chinese Academy of Sciences, and the first prize of Shanghai Science and Technology Progress Award.
Researchers discuss the testing process Photo courtesy of the interviewer
The key technology behind lunar fire detection
With the exploration experience of the previous lunar exploration project, the team also undertook the development of the Tianwen-1 Mars rover "Zhurong".
Among the payloads of Zhurong weighing 25 kilograms, the Mars surface composition detector developed by the space active photoelectric payload development team of the Shanghai Institute of Technology accounted for 15 kilograms. "Although the weight of 15 kilograms is given, in fact, this weight is still relatively demanding, the load has multiple functions such as microscopic camera, transient plasma spectrum detection and calibration, laser emission and self-focusing adjustment, and can withstand harsh conditions such as landing impact and low temperature." Shu Rong recently introduced to reporters.
As one of the core scientific payloads of the rover, the detector should use laser-induced plasma spectroscopy technology to measure rock elements and their content and detect the geological composition of Mars.
Shu Rong said that the working principle of the component detector is to focus a laser to the target, and use high temperature to vaporize it to produce plasma. In the process of cooling, the spectral information that produces radiation is measured to know what its elements are. "However, the Mars surface composition detector is installed outside the cabin, and it will reach minus 96 degrees Celsius at night, which is relatively easy to break the equipment at this low temperature, and how to withstand low temperatures while maintaining accuracy is a big problem."
In his opinion, the biggest difficulty in this load at the beginning is the problem of heat source. Because there is an isotope heat source on the lunar rover, the spectrometer on board the rover will not encounter this situation, but the rover does not contain an isotope heat source. Therefore, in the development process, in order to adapt to low temperature conditions, the team did countless experiments, only taking one of the links - the lens holder of the telescope as an example, and designed a variety of schemes to repeatedly compare, consider, and verify, and finally made a decision.
Not only the lunar and deep space exploration related technical research, but also the success of the continent's first quantum science experiment satellite Micius also has some thrilling research and development stories.
Micius Quantum Science Experiment Satellite payload field test (profile photo)
At that time, Zhang Liang, a researcher at the Shanghai Institute of Technology and a doctoral student and head of the quantum optical transmission project of the medium and high-orbit quantum science experiment satellite, and his brothers often went to Qinghai Lake. "Micius is mainly involved in quantum communication, why should we do it? Because it provides a physically and absolutely secure way to generate passwords, thus guaranteeing secure communication. ”
He explained to reporters that the reason for making quantum satellites is mainly affected by the curvature of the ground earth and ground optical fibers when on the ground, which will lose quantum signals, so the distance of quantum communication on the ground is only hundreds of kilometers, so it is difficult to even cross the whole of China, let alone the world, "so we want to use satellites to achieve quantum communication and achieve global cryptographic sharing."
However, verification and experimentation are not so easy. Once in order to simulate the state of the payload flying on the satellite, the team released a hot air balloon at night, but they did not expect that the location was selected in a wind vent, the balloon suddenly flew up more than 20 meters, and when it was recovered, it slammed into the ground, which scared them a lot.
"Because the quantum signal is very weak, we want to minimize its loss, that is, how to make the quantum signal from the satellite as much as possible to reduce the loss, aim to the ground, improve the accuracy, this is a difficult point we have to solve." Zhang Liang explained.
At present, the team has also formed a pyramid-shaped old, middle-aged and young group team. "Post-50s" academician Wang Jianyu carefully guided the top-level planning and design of the project, including the backbone of the "post-70s" Shu Rong and He Zhiping, and the "post-80s" and "post-90s" post-waves such as Huang Genghua and Zhang Liang. At this stage, the team is carrying out the development of follow-up engineering tasks such as lunar and deep space exploration, medium and high orbit quantum satellites, and space infrastructure.
It can be used in the civil field
In addition to the aerospace field, meteorology and geology are also inseparable from the instruments developed by the team.
In the laboratory of the Shanghai Institute of Technology located in Yutian Road, Hongkou District, Shanghai, the 300-kilogram Gaofen-7 satellite laser altimeter prototype occupies a lot of space in the laboratory, and it is this instrument that can improve the three-dimensional mapping accuracy from 1:50,000 scale to 1:10,000, and the plane positioning accuracy jumps directly from the 50-meter accuracy scale to less than 10 meters.
Team members told the first financial reporter that traditional passive imaging satellites can only roughly sense the target distance, and the photos taken are difficult to accurately fit the target surface, but the elevation control points collected by this laser altimeter are like pushpins on the photo, which can fix the image to the three-dimensional coordinate system. Since its launch in November 2019, the laser altimeter has provided millions of accurate elevation control points to mapping departments, significantly reducing the amount of field work for mappers.
Huang Genghua, chief designer of the Gaofen No. 7 02 star laser altimeter, made an analogy to describe the accuracy, which is equivalent to from the top of the Oriental Pearl, to accurately know and keep which stripe the laser falls on the ground milk carton barcode, there can be no misalignment. He introduced that multidisciplinary and cross-unit scientific research cooperation also makes the development of instruments possible, for example, the assembly accuracy of key optical lenses can reach the order of microns, thousand-fold thinner than a hair.
Gold leaf/photo
Huang Genghua believes that laser altimeters can be used not only for large surveying and mapping satellites, but also for small commercial satellite constellations. However, first of all, it is necessary to solve the problems of light miniaturization and low cost, such as replacing materials and adjusting the structure, etc., to reduce the weight of the 300 kg instrument to less than 40 kg, and the cost is reduced to the affordable range of commercial spaceflight.