From today, there is another Chinese satellite in the vast space. In the early morning of November 15, the fourth star of our country’s second-generation polar-orbiting meteorological satellite Fengyun-3 was successfully launched in Taiyuan. And this star, like the other 15 Fengyun meteorological satellites launched by our country, embodies the glory and dream of Shanghai astronauts.
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Compared with its three "older brothers", Fengyun-3D satellite can be said to have undergone a reborn change. A variety of payloads have been upgraded, and infrared hyperspectral atmospheric detectors, hyperspectral greenhouse gas monitors, and wide-angle aurora imagers have been added, thus gradually meeting the growing new needs of atmospheric detection accuracy, greenhouse gas monitoring capabilities, and comprehensive space environment detection capabilities in the meteorological field. At the Shanghai Academy of Aerospace Technology, the reporter heard the story behind this brand new "China Star".
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Busy as if obsessed
The Fengyun-3 D-star is loaded with a total of 10 payloads. Compared with the C-star, the D-star has added 4 payloads, and there are 2 that have improved performance and upgraded. Many people think that the Fengyun-3 D-star is a mature model, but the indicator of the 6 new payloads is to reach the international advanced level. The technical status is complex and the development progress is extremely tight.
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"The high-precision 250-meter split window of the medium-resolution spectral imager is the first in the world, the signal-to-noise ratio of the hyperspectral greenhouse gas monitor in the same spectral range is twice as high as that of GOSAT, the infrared hyperspectral atmospheric detector is consistent with the CrIS index, and the wide-angle aurora imager and ionospheric photometer are both developed for the first time in our country…" Li Yefei, the general director of Fengyun No. 3, used a series of first conveys the extraordinary "origin" of the D star.
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The six new loads all start from the plan, go through the initial prototype development, and then go through the normal development. The determination of each technical status has to go through countless technical coordination. In the project implementation stage, each load has to sign the interface data sheet, and each load has mandatory inspection points, calibration tests, and ring mold tests.
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"Sometimes it’s like being obsessed with something all day long. If you say you go to work overtime, you go to work overtime, and if you say you go to work at home, you leave. We really don’t understand." Zhao Qichang, the chief designer of Fengyun No. 3 D star payload, missed the first enrollment of his three-year-old son while working overtime. Faced with his family’s complaints, he can only make up for his "sins" by doing more housework and smiling more.
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It cannot be looked down upon abroad
With so many new payloads facing such a short development cycle, the progress of the whole satellite is facing challenges, and the progress of the infrared hyperspectral atmospheric detector and the medium resolution spectral imager is particularly tight. "In the first half of 2015, we had to go to the payload unit every day to follow the production, and over time, this batch of designers and the payload unit designers also established a special friendship." Zhao Qichang recalled this period of time deeply.
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The biggest feature of the Fengyun-3 D satellite data is the global broadcast. Scientists in the global meteorological field are using the Fengyun-3 data, and any problems will be exposed in front of people all over the world. Therefore, the user’s product quality and data quality requirements for the D satellite can be described as "abnormal", from data preprocessing to data application are unmatched by other satellite users, which requires the team to also have data processing capabilities and cannot be underestimated by foreign countries.
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The Shanghai Aerospace Technology Team started from the original code of the data to analyze, calculate the sensitivity, signal to noise ratio, calibration accuracy, stability, linearity of the instrument, etc., and compare, discuss, negotiate, and finally agree with the user and the load undertaking unit. Users also often praise the Fengyun team as a generalist, not only understanding machines, heat, light, electricity, magnetism, and mechanisms, but also data processing, which is really amazing. However, these are all completed under the condition that the Fengyun team is understaffed. With such a limited number of people, it is really not easy to be both "father" and "mother". But when the satellite is operating stably in orbit, the payload data plays a role in the national economy and people’s livelihood, and international colleagues talk about the evaluation of Fengyun-3’s significant contribution to the world’s numerical weather forecasting, all the ups and downs in the process are nothing.
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Overcoming micro-vibration difficulties
Fengyun-3 D satellite is loaded with more than ten loads and more than ten moving parts at the same time. The abnormally complex vibration environment leads to an abnormally prominent contradiction in the dynamic compatibility of the star. If you don’t pay attention, the wish of one-star multi-function will not only not be realized, but multiple loads will interfere with each other. In particular, the loaded interferometric infrared hyperspectral detector is the first application on our country’s low-orbit remote sensing satellite. It has the advantages of high spatial resolution and high spectral resolution. Even small vibrations greatly reduce its performance.
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"In order to solve the dynamic compatibility problem of multi-load coexistence, provide an ultra-quiet working environment for sensitive load detectors, and improve the accuracy of infrared hyperspectral load detection, we developed a micro-vibration monitoring and suppression system, and applied the’liquid damping vibration isolation ‘technology on domestic remote sensing satellites for the first time to achieve resonant peak and high-frequency vibration suppression." Liu Xingtian, the general development unit of Fengyun Satellite, Shanghai Aerospace 509 Institute, is also a direct participant in the research of micro-vibration monitoring and suppression technology, and has a fresh memory of the process of micro-vibration research.
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After the research and demonstration of the on-board dynamic spectrum characteristics, the potential mutual interference between the loads was effectively avoided. At the same time, the development of the relaxed "liquid damping vibration isolation" technology can not only effectively control the magnification at the resonance peak, but also attenuate the high-frequency vibration by more than 90%, overcoming the technical problems of traditional passive vibration reduction. At the same time, the research team repeatedly carried out a series of comparison tests, parameter adjustment one by one, and test verification one by one, finally ensuring the harmonious coexistence of multiple loads in orbit and ensuring the imaging performance of the satellite.
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As a new generation polar-orbiting meteorological satellite in our country, since the launch of Fengyun-3 in 2008, its satellite remote sensing data has provided an important basis for national and local government decision-making. It has played an important role in the meteorological service guarantee of major events such as the "Belt and Road Initiative" International Cooperation Summit Forum, the 13th National Games, the 9th BRICS Leaders’ Meeting, and the 19th National Congress of the Communist Party of China.
