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The Yaogan-30 constellation has already been the subject of two previous articles , but this should be the last: Following the launch of the seventh trio of satellites, the constellation now has six orbital planes distributed evenly. It has therefore reached its full capacity and its final form.
The six orbital planes of the constellation
Having only six orbital planes with seven launches might seem odd. As pointed out in a previous article , the third and fourth launches injected their satellites into the same orbital plane, and created a "train" of five satellites that follow each other very closely. This makes it possible to have an extremely high revisit rate when this train passes over a region of interest.
A satellite out of service
The other particularity of the constellation is that one of the satellites of the sixth group is out of service, or in any case that its propulsion system is: Yaogan 30T (international designator 2020-021C) is not correctly positioned in its orbital plane. Normally the three satellites of the same plane are phased at 120 ° from each other, to maximize the coverage of the constellation. On the other hand, Yaogan 30T and 30S are currently very close to each other, which makes one of the two redundant.
The one with the problem is Yaogan 30T, as can be seen in this graph comparing the orbital elements of the sixth group:
Evolution over time of the number of revolutions per day for the 6th group
The 30T satellite has not made any maneuvers since it entered orbit, and therefore performs more revolutions per day around the Earth than the other two. This means that its position in the orbital plane is constantly changing, and the fact that it is currently close to 30S is only a coincidence. He will move away from it in the thick of time.
We can compare with what happens in the case of a group whose three satellites are perfectly functional, as is the case for the last launch:
Evolution over time of the number of revolutions per day for the 7th group
The satellites were launched together and therefore at the beginning the curves are confused. Then they used their thrusters to maneuver and each have a different number of revolutions per day. This allowed them to position themselves on a different sector of the orbit. They let this position drift until the 120 ° phase between the satellites was reached, then froze their orbital configuration by maneuvering again so that they all had exactly the same number of revolutions per day. This ensures that they stay synchronized in their orbit.
It is possible that China will end up replacing the satellite that is out of service, because that would improve the coverage offered by the constellation, making it more regular with fewer interruptions. This would be a good opportunity for one of the new small Chinese launchers like the CZ-11 rocket, since a single Yaogan-30 type satellite represents a small payload.
Blanket
Speaking of coverage, let's take a look at what the constellation can do. Given its inclination, it is optimized to observe the environment close to China, in particular the approaches to its Pacific coast. Taipei, the capital of Taiwan, is therefore a very representative area of interest, especially since the recent rearmament efforts of the Republic of China with the United States have heightened tensions in the region.
Based on the 3D models of the satellites that Chinese TV broadcast, they don't appear to carry radar or imaging systems, so they are probably used for electronic intelligence, possibly with a communications function as well. These types of sensors generally need to see their target at an angle of incidence of at least 5 °. Based on this assumption, we can calculate Taipei's coverage over a 24-hour period:
In cyan, the periods of coverage.
We see that the coverage is almost constant, with the longest interruption lasting around 30 minutes, and most interruptions lasting 10 minutes every half hour. The following video shows satellite position and coverage opportunities (in the form of a purple link between the satellite and the ground):
However, if we assume that the satellites carry an imaging payload, then the constraints on the angle of incidence are greater, which reduces the coverage. By taking 30 ° as the minimum angle of incidence, it then becomes:
In cyan, the periods of coverage.
The result is much more sparse, which is all in all logical because each satellite must be much higher above the horizon to take an image. However, there is still a very high revisit rate with imaging opportunities every 30 minutes. This allows almost permanent cover, and would give China the ability to track the mobile military assets of its adversaries such as missile batteries or ships.
Plans for the future
This revisiting rate is already the highest among all known constellations in China or elsewhere, but the middle country does not intend to stop there, as academician Li Deren explains in a recent interview :
“The first step is to provide local (local) coverage from the South China Sea to the North China region . This requires around 20 remote sensing satellites and 1 to 3 communication satellites in geostationary orbit to achieve a time resolution of 15 minutes. High-resolution target images and sub-meter navigation and positioning accuracy are sent to users' mobile phones and other smart terminals;
The second step is regional coverage of China and neighboring countries along the Belt and Road. This requires a hundred remote sensing satellites. Among them, half of the remote sensing satellites are optical satellites and the other half are radar satellites to ensure the broadcasting of images day and night, plus 150 communication satellites;
The third stage is global . To achieve a worldwide service, it is estimated that 200 remote sensing satellites and 300 communications satellites will be required. The service index is the time resolution of 5 minutes, that is, the required image target is found within 5 minutes, the resolution and navigation accuracy reach 0.5m, and the time In-orbit processing and communication time is less than 1 minute before being delivered to the user's mobile phone. "
Yaogan-30 is the first step, with 21 satellites optimized for the Chinese coastline. However, it does not hit a revisit every 15 minutes, so Mr. Deren may be talking about another constellation that will be launching in the near future. The use of geostationary satellites as relays, in order to minimize the latency of the system, can on the other hand already be implemented on Yaogan-30.
Li Deren also explains that future developments will bring together the traditionally separate functions of communication, Earth observation and positioning in a single system, and that the data will be sent directly to end-user phones to minimize latency and maximize their impact:
" The perceived data will be intelligently processed to provide users with the function of PNTRC, P representing the position, N the navigation route, T the time, R the remote sensing image [Remote sensing], and C the communication, c ' that is, this information can be sent to the receiving device in your hand. "
This plan looks like two drops of water to the American ambitions to equip itself with a multi-layered military constellation to ensure communications, anti-ballistic missile warning and Earth observation. Given the extent of Chinese investments in the field, we must not doubt that they will manage to develop an equivalent system, and that therefore we have not finished hearing about large constellations of Chinese satellites.
www.eastpendulum.com
The six orbital planes of the constellation
Having only six orbital planes with seven launches might seem odd. As pointed out in a previous article , the third and fourth launches injected their satellites into the same orbital plane, and created a "train" of five satellites that follow each other very closely. This makes it possible to have an extremely high revisit rate when this train passes over a region of interest.
A satellite out of service
The other particularity of the constellation is that one of the satellites of the sixth group is out of service, or in any case that its propulsion system is: Yaogan 30T (international designator 2020-021C) is not correctly positioned in its orbital plane. Normally the three satellites of the same plane are phased at 120 ° from each other, to maximize the coverage of the constellation. On the other hand, Yaogan 30T and 30S are currently very close to each other, which makes one of the two redundant.
The one with the problem is Yaogan 30T, as can be seen in this graph comparing the orbital elements of the sixth group:
Evolution over time of the number of revolutions per day for the 6th group
The 30T satellite has not made any maneuvers since it entered orbit, and therefore performs more revolutions per day around the Earth than the other two. This means that its position in the orbital plane is constantly changing, and the fact that it is currently close to 30S is only a coincidence. He will move away from it in the thick of time.
We can compare with what happens in the case of a group whose three satellites are perfectly functional, as is the case for the last launch:
Evolution over time of the number of revolutions per day for the 7th group
The satellites were launched together and therefore at the beginning the curves are confused. Then they used their thrusters to maneuver and each have a different number of revolutions per day. This allowed them to position themselves on a different sector of the orbit. They let this position drift until the 120 ° phase between the satellites was reached, then froze their orbital configuration by maneuvering again so that they all had exactly the same number of revolutions per day. This ensures that they stay synchronized in their orbit.
It is possible that China will end up replacing the satellite that is out of service, because that would improve the coverage offered by the constellation, making it more regular with fewer interruptions. This would be a good opportunity for one of the new small Chinese launchers like the CZ-11 rocket, since a single Yaogan-30 type satellite represents a small payload.
Blanket
Speaking of coverage, let's take a look at what the constellation can do. Given its inclination, it is optimized to observe the environment close to China, in particular the approaches to its Pacific coast. Taipei, the capital of Taiwan, is therefore a very representative area of interest, especially since the recent rearmament efforts of the Republic of China with the United States have heightened tensions in the region.
Based on the 3D models of the satellites that Chinese TV broadcast, they don't appear to carry radar or imaging systems, so they are probably used for electronic intelligence, possibly with a communications function as well. These types of sensors generally need to see their target at an angle of incidence of at least 5 °. Based on this assumption, we can calculate Taipei's coverage over a 24-hour period:
In cyan, the periods of coverage.
We see that the coverage is almost constant, with the longest interruption lasting around 30 minutes, and most interruptions lasting 10 minutes every half hour. The following video shows satellite position and coverage opportunities (in the form of a purple link between the satellite and the ground):
However, if we assume that the satellites carry an imaging payload, then the constraints on the angle of incidence are greater, which reduces the coverage. By taking 30 ° as the minimum angle of incidence, it then becomes:
In cyan, the periods of coverage.
The result is much more sparse, which is all in all logical because each satellite must be much higher above the horizon to take an image. However, there is still a very high revisit rate with imaging opportunities every 30 minutes. This allows almost permanent cover, and would give China the ability to track the mobile military assets of its adversaries such as missile batteries or ships.
Plans for the future
This revisiting rate is already the highest among all known constellations in China or elsewhere, but the middle country does not intend to stop there, as academician Li Deren explains in a recent interview :
“The first step is to provide local (local) coverage from the South China Sea to the North China region . This requires around 20 remote sensing satellites and 1 to 3 communication satellites in geostationary orbit to achieve a time resolution of 15 minutes. High-resolution target images and sub-meter navigation and positioning accuracy are sent to users' mobile phones and other smart terminals;
The second step is regional coverage of China and neighboring countries along the Belt and Road. This requires a hundred remote sensing satellites. Among them, half of the remote sensing satellites are optical satellites and the other half are radar satellites to ensure the broadcasting of images day and night, plus 150 communication satellites;
The third stage is global . To achieve a worldwide service, it is estimated that 200 remote sensing satellites and 300 communications satellites will be required. The service index is the time resolution of 5 minutes, that is, the required image target is found within 5 minutes, the resolution and navigation accuracy reach 0.5m, and the time In-orbit processing and communication time is less than 1 minute before being delivered to the user's mobile phone. "
Yaogan-30 is the first step, with 21 satellites optimized for the Chinese coastline. However, it does not hit a revisit every 15 minutes, so Mr. Deren may be talking about another constellation that will be launching in the near future. The use of geostationary satellites as relays, in order to minimize the latency of the system, can on the other hand already be implemented on Yaogan-30.
Li Deren also explains that future developments will bring together the traditionally separate functions of communication, Earth observation and positioning in a single system, and that the data will be sent directly to end-user phones to minimize latency and maximize their impact:
" The perceived data will be intelligently processed to provide users with the function of PNTRC, P representing the position, N the navigation route, T the time, R the remote sensing image [Remote sensing], and C the communication, c ' that is, this information can be sent to the receiving device in your hand. "
This plan looks like two drops of water to the American ambitions to equip itself with a multi-layered military constellation to ensure communications, anti-ballistic missile warning and Earth observation. Given the extent of Chinese investments in the field, we must not doubt that they will manage to develop an equivalent system, and that therefore we have not finished hearing about large constellations of Chinese satellites.
La constellation Yaogan-30 est terminée
La Chine a récemment lancé le 7e et dernier groupe de satellites Yaogan-30. Analysons maintenant les capacités de la constellation.
www.eastpendulum.com
