China News Agency, Beijing, February 27th (Ma Shuaisha and Chen Baojuan) Land Exploration No. 1 Group 01 B star successfully entered the predetermined orbit on the 27th with the Long March 4C carrier rocket, and will run in formation with the A star launched in January. Provide strong space technical support in the fields of geological disasters, land survey, earthquake assessment, disaster prevention and mitigation, basic surveying and mapping, forestry survey, etc.
Double star join hands 1+1>2
As a formation satellite, the biggest difficulty lies in the control of the double-satellite orbiting mode.
"Just like the pair figure skating event in the Winter Olympics, two athletes jumped and rotated hand in hand to complete difficult dance moves while synchronizing high-speed skating on the ice." Satellite of the Control Institute of the Eighth Academy of China Aerospace Science and Technology Corporation Deputy Chief Designer Wang Wenyan explained, "The A and B double stars in the orbit also have a pair of invisible hands together, which we call the 'baseline'."
To accurately see the height changes of mountains and vegetation over a period of time, it is necessary for the two satellites to return to the same target point and maintain the same relative positional relationship after each regression cycle.
This invisible "baseline" is also a ruler, which specifies the relative positional relationship of the binary stars each time they arrive at the predetermined observation site.
Wang Wenyan said, "When flying around, the two satellites are close to each other, and observing at the same time is like two eyes of a person, one eye can only see the plane, and both eyes can see the height and depth, which can be used for steep highlands, Mapping of forest vegetation, etc.”
The A and B double stars will also change the formation configuration according to the different latitudes of the surveyed and mapped areas, so as to realize the switching of "protagonist" and "supporting role".
Wang Wenyan said, "For example, when surveying and mapping at low latitudes, star B rotates relative to star A at a certain distance and angle; when it reaches middle latitudes, star A rotates relative to star B in another state, which can maximize the Give full play to the working capabilities of the two satellites to achieve the effect of using the optimal observation baseline to achieve national terrestrial observation."
How "Big Man" Can Dance "Space Waltz"
In order to make Shuangxing dance this "space waltz" well, the Eighth Academy's attitude and orbit control sub-system team proposed and applied long-baseline formation and strict return to orbit collaborative control technology, so that Shuangxing can "dance" safely and accurately "appear" .
Du Yaoke, the chief designer of the satellite attitude and orbit control sub-system of the Land Exploration-1 Group 01, said that the "long baseline" is a major feature of the Land Exploration-1 Group 01 satellite that is different from the previous double-star formation.
Compared with other synthetic aperture radar satellites, the radars carried by this group of satellites are L-band and have longer wavelengths. The distance between the two satellites required to fly around during surveying and mapping is between 2 and 6 kilometers, plus the "size" of the satellites themselves. It is also relatively large, causing the entire double star configuration to be several times larger, but the control accuracy requirements are more stringent.
In this regard, the research and development team applied a combination of high-precision accelerometers and access to closed-loop control.
"Similar to the radar system when a car is driving autonomously, it feeds back the speed increment information of the satellite in real time, allowing the satellite to autonomously calculate whether to 'accelerate', 'decelerate' or 'turn' in the next step." Du Yaoke said.
At the same time, in order to achieve high-precision space-time revisit of the observation target point, the satellite needs to run on a strict regression orbit designed by precise calculation.
In the orbiting mode, the two satellites must not only maintain the "absolute lane", but also ensure a relative safe distance. This is the strict return-orbit coordinated control technology.
The R&D team has formulated a strategy for the main star to maintain the pipeline, and the auxiliary star to form an orbiting flight formation with respect to the main star. Measures such as fault classification diagnosis and autonomous safety escape provide multiple security guarantees.
In addition, in order to enable the two "big men" to "run fast" and "fine-tune in small steps" and execute the control system instructions quickly and accurately, the development team configured 36 thrusters for each of the two stars, and adopted " 5N+1N" combination strategy.
"The 5N thruster is powerful, and the 1N thruster is more accurate, which can take into account the control efficiency and control accuracy." Du Yaoke said.
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